Linux Filesystem Hierarchy Version 0.65 Binh Nguyen 2004-07-30 This document outlines the set of requirements and guidelines for file and directory placement under the Linux operating system according to those of the FSSTND v2.3 final (January 29, 2004) and also its actual implementation on an arbitrary system. It is meant to be accessible to all members of the Linux community, be distribution independent and is intended to discuss the impact of the FSSTND and how it has managed to increase the efficiency of support interoperability of applications, system administration tools, development tools, and scripts as well as greater uniformity of documentation for these systems. Copyright 2003 Binh Nguyen Trademarks are owned by their owners. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License". ----------------------------------------------------------------------------- Table of Contents Source and pre-formatted versions available 1. Linux Filesystem Hierarchy 1.1. Foreward 1.2. The Root Directory 1.3. /bin 1.4. /boot 1.5. /dev 1.6. /etc 1.7. /home 1.8. /initrd 1.9. /lib 1.10. /lost+found 1.11. /media 1.12. /mnt 1.13. /opt 1.14. /proc 1.15. /root 1.16. /sbin 1.17. /usr 1.18. /var 1.19. /srv 1.20. /tmp Glossary A. UNIX System V Signals B. Sources C. About the Author D. Contributors E. Disclaimer F. Donations G. Feedback H. GNU Free Documentation License H.1. PREAMBLE H.2. APPLICABILITY AND DEFINITIONS H.3. VERBATIM COPYING H.4. COPYING IN QUANTITY H.5. MODIFICATIONS H.6. COMBINING DOCUMENTS H.7. COLLECTIONS OF DOCUMENTS H.8. AGGREGATION WITH INDEPENDENT WORKS H.9. TRANSLATION H.10. TERMINATION H.11. FUTURE REVISIONS OF THIS LICENSE H.12. ADDENDUM: How to use this License for your documents ----------------------------------------------------------------------------- Source and pre-formatted versions available The source code and other machine readable formats of this book can be found on the Internet at the Linux Documentation Project home page [http:// www.tldp.org] http://www.tldp.org The latest version of this document can be found at [http://cvsview.tldp.org/index.cgi/LDP/guide/docbook/ Linux-Filesystem-Hierarchy/] http://cvsview.tldp.org/index.cgi/LDP/guide/ docbook/Linux-Filesystem-Hierarchy/ ----------------------------------------------------------------------------- Chapter 1. Linux Filesystem Hierarchy 1.1. Foreward When migrating from another operating system such as Microsoft Windows to another; one thing that will profoundly affect the end user greatly will be the differences between the filesystems. What are filesystems? A filesystem is the methods and data structures that an operating system uses to keep track of files on a disk or partition; that is, the way the files are organized on the disk. The word is also used to refer to a partition or disk that is used to store the files or the type of the filesystem. Thus, one might say I have two filesystems meaning one has two partitions on which one stores files, or that one is using the extended filesystem, meaning the type of the filesystem. The difference between a disk or partition and the filesystem it contains is important. A few programs (including, reasonably enough, programs that create filesystems) operate directly on the raw sectors of a disk or partition; if there is an existing file system there it will be destroyed or seriously corrupted. Most programs operate on a filesystem, and therefore won't work on a partition that doesn't contain one (or that contains one of the wrong type). Before a partition or disk can be used as a filesystem, it needs to be initialized, and the bookkeeping data structures need to be written to the disk. This process is called making a filesystem. Most UNIX filesystem types have a similar general structure, although the exact details vary quite a bit. The central concepts are superblock, inode, data block, directory block, and indirection block. The superblock contains information about the filesystem as a whole, such as its size (the exact information here depends on the filesystem). An inode contains all information about a file, except its name. The name is stored in the directory, together with the number of the inode. A directory entry consists of a filename and the number of the inode which represents the file. The inode contains the numbers of several data blocks, which are used to store the data in the file. There is space only for a few data block numbers in the inode, however, and if more are needed, more space for pointers to the data blocks is allocated dynamically. These dynamically allocated blocks are indirect blocks; the name indicates that in order to find the data block, one has to find its number in the indirect block first. Like UNIX, Linux chooses to have a single hierarchical directory structure. Everything starts from the root directory, represented by /, and then expands into sub-directories instead of having so-called 'drives'. In the Windows environment, one may put one's files almost anywhere: on C drive, D drive, E drive etc. Such a file system is called a hierarchical structure and is managed by the programs themselves (program directories), not by the operating system. On the other hand, Linux sorts directories descending from the root directory / according to their importance to the boot process. If you're wondering why Linux uses the frontslash / instead of the backslash \ as in Windows it's because it's simply following the UNIX tradition. Linux, like Unix also chooses to be case sensitive. What this means is that the case, whether in capitals or not, of the characters becomes very important. So this is not the same as THIS. This feature accounts for a fairly large proportion of problems for new users especially during file transfer operations whether it may be via removable disk media such as floppy disk or over the wire by way of FTP. The filesystem order is specific to the function of a file and not to its program context (the majority of Linux filesystems are 'Second Extended File Systems', short 'EXT2' (aka 'ext2fs' or 'extfs2') or are themselves subsets of this filesystem such as ext3 and Reiserfs). It is within this filesystem that the operating system determines into which directories programs store their files. If you install a program in Windows, it usually stores most of its files in its own directory structure. A help file for instance may be in C:\Program Files\[program name]\ or in C:\Program Files\[program-name]\help or in C:\ Program Files\[program -name]\humpty\dumpty\doo. In Linux, programs put their documentation into /usr/share/doc/[program-name], man(ual) pages into /usr/ share/man/man[1-9] and info pages into /usr/share/info. They are merged into and with the system hierarchy. As all Linux users know, unless you mount a partition or a device, the system does not know of the existence of that partition or device. This might not appear to be the easiest way to provide access to your partitions or devices, however it offers the advantage of far greater flexibility when compared to other operating systems. This kind of layout, known as the unified filesystem, does offer several advantages over the approach that Windows uses. Let's take the example of the /usr directory. This sub-directory of the root directory contains most of the system executables. With the Linux filesystem, you can choose to mount it off another partition or even off another machine over the network using an innumerable set of protocols such as NFS (Sun), Coda (CMU) or AFS (IBM). The underlying system will not and need not know the difference. The presence of the /usr directory is completely transparent. It appears to be a local directory that is part of the local directory structure. Compliance requires that: +---------+-----------------+-------------+ | | shareable | unshareable | +---------+-----------------+-------------+ |static | /usr | /etc | | | /opt | /boot | +---------+-----------------+-------------+ |variable | /var/mail | /var/run | | | /var/spool/news | /var/lock | +---------+-----------------+-------------+ "Shareable" files are defined as those that can be stored on one host and used on others. "Unshareable" files are those that are not shareable. For example, the files in user home directories are shareable whereas device lock files are not. "Static" files include binaries, libraries, documentation files and other files that do not change without system administrator intervention. "Variable" files are defined as files that are not static. Another reason for this unified filesystem is that Linux caches a lot of disk accesses using system memory while it is running to accelerate these processes. It is therefore vitally important that these buffers are flushed (get their content written to disk), before the system closes down. Otherwise files are left in an undetermined state which is of course a very bad thing. Flushing is achieved by 'unmounting' the partitions during proper system shutdown. In other words, don't switch your system off while it's running! You may get away with it quite often, since the Linux file system is very robust, but you may also wreak havoc upon important files. Just hit ctrl-alt-del or use the proper commands (e.g. shutdown, poweroff, init 0). This will shut down the system in a decent way which will thus, guarantee the integrity of your files. Many of us in the Linux community have come to take for granted the existence of excellent books and documents about Linux, an example being those produced by the Linux Documentation Project. We are used to having various packages taken from different sources such as Linux FTP sites and distribution CD-ROMs integrate together smoothly. We have come to accept that we all know where critical files like mount can be found on any machine running Linux. We also take for granted CD-ROM based distributions that can be run directly from the CD and which consume only a small amount of physical hard disk or a RAM disk for some variable files like /etc/passwd, etc. This has not always been the case. During the adolescent years of Linux during the early to mid-90s each distributor had his own favorite scheme for locating files in the directory hierarchy. Unfortunately, this caused many problems. The Linux File System Structure is a document, which was created to help end this anarchy. Often the group, which creates this document or the document itself, is referred to as the FSSTND. This is short for file system standard". This document has helped to standardize the layout of file systems on Linux systems everywhere. Since the original release of the standard, most distributors have adopted it in whole or in part, much to the benefit of all Linux users. Since the first draft of the standard, the FSSTND project has been coordinated by Daniel Quinlan and development of this standard has been through consensus by a group of developers and Linux enthusiasts. The FSSTND group set out to accomplish a number of specific goals. The first goal was to solve a number of problems that existed with the current distributions at the time. Back then, it was not possible to have a shareable /usr partition, there was no clear distinction between /bin and /usr/bin, it was not possible to set up a diskless workstation, and there was just general confusion about what files went where. The second goal was to ensure the continuation of some reasonable compatibility with the de-facto standards already in use in Linux and other UNIX-like operating systems. Finally, the standard had to gain widespread approval by the developers, distributors, and users within the Linux community. Without such support, the standard would be pointless, becoming just another way of laying out the file system. Fortunately, the FSSTND has succeeded though there are also some goals that the FSSTND project did not set out to achieve. The FSSTND does not try to emulate the scheme of any specific commercial UNIX operating system (e.g. SunOS, AIX, etc.) Furthermore, for many of the files covered by the FSSTND, the standard does not dictate whether the files should be present, merely where the files should be if they are present. Finally, for most files, the FSSTND does not attempt to dictate the format of the contents of the files. (There are some specific exceptions when several different packages may need to know the file formats to work together properly. For example, lock files that contain the process ID of the process holding the lock.) The overall objective was to establish the location where common files could be found, if they existed on a particular machine. The FSSTND project began in early August 1993. Since then, there have been a number of public revisions of this document. The latest, v2.3 was released on January 29, 2004. If you're asking "What's the purpose of all this? Well, the answer depends on who you are. If you are a Linux user, and you don't administrate your own system then the FSSTND ensures that you will be able to find programs where you'd expect them to be if you've already had experience on another Linux machine. It also ensures that any documentation you may have makes sense. Furthermore, if you've already had some experience with Unix before, then the FSSTND shouldn't be too different from what you're currently using, with a few exceptions. Perhaps the most important thing is that the development of a standard brings Linux to a level of maturity authors and commercial application developers feel they can support. If you administer your own machine then you gain all the benefits of the FSSTND mentioned above. You may also feel more secure in the ability of others to provide support for you, should you have a problem. Furthermore, periodic upgrades to your system are theoretically easier. Since there is an agreed-upon standard for the locations of files, package maintainers can provide instructions for upgrading that will not leave extra, older files lying around your system inhabiting valuable disk space. The FSSTND also means that there is more support from those providing source code packages for you to compile and install yourself. The provider knows, for example, where the executable for sed is to be found on a Linux machine and can use that in his installation scripts or Makefiles. If you run a large network, the FSSTND may ease many of your NFS headaches, since it specifically addresses the problems which formerly made shared implementations of /usr impractical. If you are a distributor, then you will be affected most by the Linux FSSTND. You may have to do a little extra work to make sure that your distribution is FSSTND-compliant, but your users (and hence your business) will gain by it. If your system is compliant, third party add-on packages (and possibly your own) will integrate smoothly with your system. Your users will, of course, gain all the benefits listed above, and many of your support headaches will be eased. You will benefit from all the discussion and thought that has been put into the FSSTND and avoid many of the pitfalls involved in designing a filesystem structure yourself. If you adhere to the FSSTND, you will also be able to take advantage of various features that the FSSTND was designed around. For example, the FSSTND makes "live" CD-ROMs containing everything except some of the files in the / and / var directories possible. If you write documentation for Linux, the FSSTND makes it much easier to do so, which makes sense to the Linux community. You no longer need to worry about the specific location of lock files on one distribution versus another, nor are you forced to write documentation that is only useful to the users of a specific distribution. The FSSTND is at least partly responsible for the recent explosion of Linux books being published. If you are a developer, the existence of the FSSTND greatly eases the possibility for potential problems. You can know where important system binaries are found, so you can use them from inside your programs or your shell scripts. Supporting users is also greatly eased, since you don't have to worry about things like the location of these binaries when resolving support issues. If you are the developer of a program that needs to integrate with the rest of the system, the FSSTND ensures that you can be certain of the steps to meet this end. For example, applications such as kermit, which access the serial ports, need to know they can achieve exclusive access to the TTY device. The FSSTND specifies a common method of doing this so that all compliant applications can work together. That way you can concentrate on making more great software for Linux instead of worrying about how to detect and deal with the differences in flavors of Linux. The widespread acceptance of the FSSTND by the Linux community has been crucial to the success of both the standard and operating system. Nearly every modern distribution conforms to the Linux FSSTND. If your implementation isn't at least partially FSSTND compliant, then it is probably either very old or you built it yourself. The FSSTND itself contains a list of some of the distributions that aim to conform to the FSSTND. However, there are some distributions that are known to cut some corners in their implementation of FSSTND. By no means does this mean that the standard itself is complete. There are still unresolved issues such as the organization of architecture-independent scripts and data files /usr/share. Up until now, the i386 has been the primary platform for Linux, so the need for standardization of such files was non-existent. The rapid progress in porting Linux to other architectures (MC680x0, Alpha, MIPS, PowerPC) suggests that this issue will soon need to be dealt with. Another issue that is under some discussion is the creation of an /opt directory as in SVR4. The goal for such a directory would be to provide a location for large commercial or third party packages to install themselves without worrying about the requirements made by FSSTND for the other directory hierarchies. The FSSTND provides the Linux community with an excellent reference document and has proven to be an important factor in the maturation of Linux. As Linux continues to evolve, so will the FSSTND. Now, that we have seen how things should be, let's take a look at the real world. As you will see, the implementation of this concept on Linux isn't perfect and since Linux has always attracted individualists who tend to be fairly opinionated, it has been a bone of contention among users for instance which directories certain files should be put into. With the arrival of different distributions, anarchy has once again descended upon us. Some distributions put mount directories for external media into the / directory, others into /mnt. Red Hat based distributions feature the /etc/sysconfig sub-hierarchy for configuration files concerning input and network devices. Other distributions do not have this directory at all and put the appropriate files elsewhere or even use completely different mechanisms to do the same thing. Some distributions put KDE into /opt/, others into /usr. But even within a given file system hierarchy, there are inconsistencies. For example, even though this was never the intention of the XFree86 group, XFree86 does indeed have its own directory hierarchy. These problems don't manifest themselves as long as you compile programs yourself. You can adapt configure scripts or Makefiles to your system's configuration or to your preference. It's a different story if you install pre-compiled packages like RPMs though. Often these are not adaptable from one file system hierarchy to another. What's worse: some RPMs might even create their own hierarchy. If you, say, install a KDE RPM from the SuSE Linux distribution on your Mandrake system, the binary will be put into /opt/ kde2/bin. And thus it won't work, because Mandrake expects it to be in /usr/ bin. There are of course ways to circumvent this problem but the current situation is clearly untenable. Thus, all the leading Linux distributors have joined the Linux Standard Base project, which is attempting to create a common standard for Linux distributions. This isn't easy, since changing the file system hierarchy means a lot of work for distributors so every distributor tries to push a standard which will allow them to keep as much of their own hierarchy as possible. The LSB will also encompass the proposals made by the Filesystem Hierarchy Standard project (FHS, former FSSTND). ----------------------------------------------------------------------------- 1.2. The Root Directory To comply with the FSSTND the following directories, or symbolic links to directories, are required in /. /bin Essential command binaries /boot Static files of the boot loader /dev Device files /etc Host-specific system configuration /lib Essential shared libraries and kernel modules /media Mount point for removeable media /mnt Mount point for mounting a filesystem temporarily /opt Add-on application software packages /sbin Essential system binaries /srv Data for services provided by this system /tmp Temporary files /usr Secondary hierarchy /var Variable data The following directories, or symbolic links to directories, must be in /, if the corresponding subsystem is installed: / -- the root directory /home User home directories (optional) /lib Alternate format essential shared libraries (optional) /root Home directory for the root user (optional) Each directory listed above is described in detail in separate subsections further on in this document. The reference system will be based upon Debian 3.0r0 (Woody), 2.4.18 kernel configured to a Redhat kernel-2.4.18-i686.config file. Hardware   + Intel Celeron 766 Processor   + MSI MS-6309 V.2.0 Mainboard   + 512MB PQI PC133 SDRAM   + 16x Lite-On LTD-165H DVD-ROM   + 40x24x10 Sony CRX175A1 CD-RW   + NVIDIA RIVA 32MB TNT2 M64   + D-Link DFE-530TX 10/100 NIC   + Realtek RTL8029(AS) 10 NIC   + Lucent Mars2 Linmodem   + C-Media CMI8738 PCI Audio Device   + Miro DC-30 VIVO   + Aopen KF-45A Miditower Case   + Acer Accufeel Keyboard   + Genius Netscroll+ Mouse   + Compaq MV500 Presario Monitor Software   + Windows XP on /dev/hda1   + FreeBSD 4.2 on /dev/hda2   + Redhat 8.0 on /dev/hda5   + Debian 3.0r0 on /dev/hda6   + Mandrake 9.1 on /dev/hda7   + Swap partition on /dev/hda8 As we all know Linux file system starts with /, the root directory. All other directories are 'children' of this directory. The partition which the root file system resides on is mounted first during boot and the system will not boot if it doesn't find it. On our reference system, the root directory contains the following sub-directories: bin/ dev/ home/ lost+found/ proc/ sbin/ usr/ cdrom/ opt/ vmlinuz boot/ etc/ lib/ mnt/ root/ tmp/ var/ dvd/ floppy/ initrd/ /tftpboot In days past it was also the home directory of 'root' but now he has been given his own directory for reasons that will be explained further on in this document. ----------------------------------------------------------------------------- 1.3. /bin Unlike /sbin, the bin directory contains several useful commands that are of use to both the system administrator as well as non-privileged users. It usually contains the shells like bash, csh, etc.... and commonly used commands like cp, mv, rm, cat, ls. For this reason and in contrast to /usr/ bin, the binaries in this directory are considered to be essential. The reason for this is that it contains essential system programs that must be available even if only the partition containing / is mounted. This situation may arise should you need to repair other partitions but have no access to shared directories (ie. you are in single user mode and hence have no network access). It also contains programs which boot scripts may depend on. Compliance to the FSSTND means that there are no subdirectories in /bin and that the following commands, or symbolic links to commands, are located there. cat Utility to concatenate files to standard output chgrp Utility to change file group ownership chmod Utility to change file access permissions chown Utility to change file owner and group cp Utility to copy files and directories date Utility to print or set the system data and time dd Utility to convert and copy a file df Utility to report filesystem disk space usage dmesg Utility to print or control the kernel message buffer echo Utility to display a line of text false Utility to do nothing, unsuccessfully hostname Utility to show or set the system's host name kill Utility to send signals to processes ln Utility to make links between files login Utility to begin a session on the system ls Utility to list directory contents mkdir Utility to make directories mknod Utility to make block or character special files more Utility to page through text mount Utility to mount a filesystem mv Utility to move/rename files ps Utility to report process status pwd Utility to print name of current working directory rm Utility to remove files or directories rmdir Utility to remove empty directories sed The `sed' stream editor sh The Bourne command shell stty Utility to change and print terminal line settings su Utility to change user ID sync Utility to flush filesystem buffers true Utility to do nothing, successfully umount Utility to unmount file systems uname Utility to print system information If /bin/sh is not a true Bourne shell, it must be a hard or symbolic link to the real shell command. The rationale behind this is because sh and bash mightn't necessarily behave in the same manner. The use of a symbolic link also allows users to easily see that /bin/sh is not a true Bourne shell. The [ and test commands must be placed together in either /bin or /usr/bin. The requirement for the [ and test commands to be included as binaries (even if implemented internally by the shell) is shared with the POSIX.2 standard. The following programs, or symbolic links to programs, must be in /bin if the corresponding subsystem is installed: csh The C shell (optional) ed The `ed' editor (optional) tar The tar archiving utility (optional) cpio The cpio archiving utility (optional) gzip The GNU compression utility (optional) gunzip The GNU uncompression utility (optional) zcat The GNU uncompression utility (optional) netstat The network statistics utility (optional) ping The ICMP network test utility (optional) If the gunzip and zcat programs exist, they must be symbolic or hard links to gzip. /bin/csh may be a symbolic link to /bin/tcsh or /usr/bin/tcsh. The tar, gzip and cpio commands have been added to make restoration of a system possible (provided that / is intact). Conversely, if no restoration from the root partition is ever expected, then these binaries might be omitted (e.g., a ROM chip root, mounting /usr through NFS). If restoration of a system is planned through the network, then ftp or tftp (along with everything necessary to get an ftp connection) must be available on the root partition. ----------------------------------------------------------------------------- 1.4. /boot This directory contains everything required for the boot process except for configuration files not needed at boot time (the most notable of those being those that belong to the GRUB boot-loader) and the map installer. Thus, the / boot directory stores data that is used before the kernel begins executing user-mode programs. This may include redundant (back-up) master boot records, sector/system map files, the kernel and other important boot files and data that is not directly edited by hand. Programs necessary to arrange for the boot loader to be able to boot a file are placed in /sbin. Configuration files for boot loaders are placed in /etc. The system kernel is located in either / or /boot (or as under Debian in /boot but is actually a symbolically linked at / in accordance with the FSSTND). /boot/boot.0300 Backup master boot record. /boot/boot.b This is installed as the basic boot sector. In the case of most modern distributions it is actually a symbolic link to one of four files /boot/ boot-bmp.b, /boot/boot-menu.b, /boot/boot-text.b, /boot/boot-compat.b which allow a user to change the boot-up schema so that it utilises a splash screen, a simple menu, a text based interface or a minimal boot loader to ensure compatibility respectively. In each case re-installation of lilo is necessary in order to complete the changes. To change the actual 'boot-logo' you can either use utilities such as fblogo or the more refined bootsplash. /boot/chain.b Used to boot non-Linux operating systems. /boot/config-kernel-version Installed kernel configuration. This file is most useful when compiling kernels on other systems or device modules. Below is a small sample of what the contents of the file looks like. CONFIG_X86=y CONFIG_MICROCODE=m CONFIG_X86_MSR=m CONFIG_MATH_EMULATION=y CONFIG_MTRR=y CONFIG_MODULES=y CONFIG_MODVERSIONS=y CONFIG_SCSI_DEBUG=m CONFIG_I2O=m CONFIG_ARCNET_ETH=y CONFIG_FMV18X=m CONFIG_HPLAN_PLUS=m CONFIG_ETH16I=m CONFIG_NE2000=m CONFIG_HISAX_HFC_PCI=y CONFIG_ISDN_DRV_AVMB1_C4=m CONFIG_USB_RIO500=m CONFIG_QUOTA=y CONFIG_AUTOFS_FS=m CONFIG_ADFS_FS=m CONFIG_AFFS_FS=m CONFIG_HFS_FS=m CONFIG_FAT_FS=y CONFIG_MSDOS_FS=y CONFIG_UMSDOS_FS=m CONFIG_FBCON_VGA=m CONFIG_FONT_8x8=y CONFIG_FONT_8x16=y CONFIG_SOUND=m CONFIG_SOUND_CMPCI=m CONFIG_AEDSP16=m As you can see, it's rather simplistic. The line begins with the configuration option and whether it's configured as part of the kernel, as a module or not at all. Lines beginning with a # symbol are comments and are not interpreted during processing. /boot/os2_d.b Used to boot to the 0S/2 operating system. /boot/map Contains the location of the kernel. /boot/vmlinuz, /boot/vmlinuz-kernel-version Normally the kernel or symbolic link to the kernel. /boot/grub This subdirectory contains the GRUB configuration files including boot-up images and sounds. GRUB is the GNU GRand Unified Bootloader, a project which intends to solve all bootup problems once and for all. One of the most interesting features, is that you don't have to install a new partition or kernel, you can change all parameters at boot time via the GRUB Console, since it knows about the filesystems. /boot/grub/device.map Maps devices in /dev to those used by grub. For example, (/dev/fd0) is represented by /dev/fd0 and (hd0, 4) is referenced by /dev/hda5. /boot/grub/grub.conf, /boot/grub/menu.lst Grub configuration file. /boot/grub/messages Grub boot-up welcome message. /boot/grub/splash.xpm.gz Grub boot-up background image. ----------------------------------------------------------------------------- 1.5. /dev /dev is the location of special or device files. It is a very interesting directory that highlights one important aspect of the Linux filesystem - everything is a file or a directory. Look through this directory and you should hopefully see hda1, hda2 etc.... which represent the various partitions on the first master drive of the system. /dev/cdrom and /dev/fd0 represent your CD-ROM drive and your floppy drive. This may seem strange but it will make sense if you compare the characteristics of files to that of your hardware. Both can be read from and written to. Take /dev/dsp, for instance. This file represents your speaker device. Any data written to this file will be re-directed to your speaker. If you try 'cat /boot/vmlinuz > / dev/dsp' (on a properly configured system) you should hear some sound on the speaker. That's the sound of your kernel! A file sent to /dev/lp0 gets printed. Sending data to and reading from /dev/ttyS0 will allow you to communicate with a device attached there - for instance, your modem. The majority of devices are either block or character devices; however other types of devices exist and can be created. In general, 'block devices' are devices that store or hold data, 'character devices' can be thought of as devices that transmit or transfer data. For example, diskette drives, hard drives and CD-ROM drives are all block devices while serial ports, mice and parallel printer ports are all character devices. There is a naming scheme of sorts but in the vast majority of cases these are completely illogical. total 724 lrwxrwxrwx 1 root root 13 Sep 28 18:06 MAKEDEV -> /sbin/MAKEDEV crw-rw---- 1 root audio 14, 14 Oct 7 16:26 admmidi0 crw-rw---- 1 root audio 14, 30 Oct 7 16:26 admmidi1 lrwxrwxrwx 1 root root 11 Oct 7 16:26 amidi -> /dev/amidi0 crw-rw---- 1 root audio 14, 13 Oct 7 16:26 amidi0 crw-rw---- 1 root audio 14, 29 Oct 7 16:26 amidi1 crw-rw---- 1 root audio 14, 11 Oct 7 16:26 amixer0 crw-rw---- 1 root audio 14, 27 Oct 7 16:26 amixer1 drwxr-xr-x 2 root root 4096 Sep 28 18:05 ataraid lrwxrwxrwx 1 root root 11 Oct 7 16:26 audio -> /dev/audio0 crw-rw---- 1 root audio 14, 4 Oct 7 16:26 audio0 crw-rw---- 1 root audio 14, 20 Oct 7 16:26 audio1 crw-rw---- 1 root audio 14, 7 Mar 15 2002 audioctl lrwxrwxrwx 1 root root 9 Oct 14 22:51 cdrom -> /dev/scd1 lrwxrwxrwx 1 root root 9 Oct 14 22:52 cdrom1 -> /dev/scd0 crw------- 1 root tty 5, 1 Jan 19 20:47 console lrwxrwxrwx 1 root root 11 Sep 28 18:06 core -> /proc/kcore crw-rw---- 1 root audio 14, 10 Oct 7 16:26 dmfm0 crw-rw---- 1 root audio 14, 26 Oct 7 16:26 dmfm1 crw-rw---- 1 root audio 14, 9 Oct 7 16:26 dmmidi0 crw-rw---- 1 root audio 14, 25 Oct 7 16:26 dmmidi1 lrwxrwxrwx 1 root root 9 Oct 7 16:26 dsp -> /dev/dsp0 crw-rw---- 1 root audio 14, 3 Oct 7 16:26 dsp0 crw-rw---- 1 root audio 14, 19 Oct 7 16:26 dsp1 crw--w---- 1 root video 29, 0 Mar 15 2002 fb0 crw--w---- 1 root video 29, 1 Mar 15 2002 fb0autodetect crw--w---- 1 root video 29, 0 Mar 15 2002 fb0current crw--w---- 1 root video 29, 32 Mar 15 2002 fb1 crw--w---- 1 root video 29, 33 Mar 15 2002 fb1autodetect crw--w---- 1 root video 29, 32 Mar 15 2002 fb1current lrwxrwxrwx 1 root root 13 Sep 28 18:05 fd -> /proc/self/fd brw-rw---- 1 root floppy 2, 0 Mar 15 2002 fd0 brw-rw---- 1 root floppy 2, 1 Mar 15 2002 fd1 crw--w--w- 1 root root 1, 7 Sep 28 18:06 full brw-rw---- 1 root disk 3, 0 Mar 15 2002 hda brw-rw---- 1 root disk 3, 64 Mar 15 2002 hdb brw-rw---- 1 root disk 22, 0 Mar 15 2002 hdc brw-rw---- 1 root disk 22, 64 Mar 15 2002 hdd drwxr-xr-x 2 root root 12288 Sep 28 18:05 ida prw------- 1 root root 0 Jan 19 20:46 initctl brw-rw---- 1 root disk 1, 250 Mar 15 2002 initrd drwxr-xr-x 2 root root 4096 Sep 28 18:05 input crw-rw---- 1 root dialout 45, 128 Mar 15 2002 ippp0 crw-rw---- 1 root dialout 45, 0 Mar 15 2002 isdn0 crw-rw---- 1 root dialout 45, 64 Mar 15 2002 isdnctrl0 crw-rw---- 1 root dialout 45, 255 Mar 15 2002 isdninfo crw------- 1 root root 10, 4 Mar 15 2002 jbm crw-r----- 1 root kmem 1, 2 Sep 28 18:06 kmem brw-rw---- 1 root cdrom 24, 0 Mar 15 2002 lmscd crw------- 1 root root 10, 0 Mar 15 2002 logibm brw-rw---- 1 root disk 7, 0 Sep 28 18:06 loop0 brw-rw---- 1 root disk 7, 1 Sep 28 18:06 loop1 crw-rw---- 1 root lp 6, 0 Mar 15 2002 lp0 crw-rw---- 1 root lp 6, 1 Mar 15 2002 lp1 crw-rw---- 1 root lp 6, 2 Mar 15 2002 lp2 crw-r----- 1 root kmem 1, 1 Sep 28 18:06 mem lrwxrwxrwx 1 root root 10 Oct 7 16:26 midi -> /dev/midi0 crw-rw---- 1 root audio 14, 2 Oct 7 16:26 midi0 crw-rw---- 1 root audio 14, 18 Oct 7 16:26 midi1 lrwxrwxrwx 1 root root 11 Oct 7 16:26 mixer -> /dev/mixer0 crw-rw-rw- 1 root root 14, 0 Nov 11 16:22 mixer0 crw-rw---- 1 root audio 14, 16 Oct 7 16:26 mixer1 lrwxrwxrwx 1 root root 11 Oct 7 06:50 modem -> /dev/ttyLT0 crw-rw---- 1 root audio 31, 0 Mar 15 2002 mpu401data crw-rw---- 1 root audio 31, 1 Mar 15 2002 mpu401stat crw-rw---- 1 root audio 14, 8 Oct 7 16:26 music crw-rw-rw- 1 root root 1, 3 Sep 28 18:06 null crw-rw-rw- 1 root root 195, 0 Jan 6 03:03 nvidia0 crw-rw-rw- 1 root root 195, 1 Jan 6 03:03 nvidia1 crw-rw-rw- 1 root root 195, 255 Jan 6 03:03 nvidiactl crw-rw---- 1 root lp 6, 0 Mar 15 2002 par0 crw-rw---- 1 root lp 6, 1 Mar 15 2002 par1 crw-rw---- 1 root lp 6, 2 Mar 15 2002 par2 -rw-r--r-- 1 root root 665509 Oct 7 16:41 pcm crw-r----- 1 root kmem 1, 4 Sep 28 18:06 port crw-rw---- 1 root dip 108, 0 Sep 28 18:07 ppp crw------- 1 root root 10, 1 Mar 15 2002 psaux crw-rw-rw- 1 root root 1, 8 Sep 28 18:06 random crw-rw---- 1 root root 10, 135 Mar 15 2002 rtc brw-rw---- 1 root cdrom 11, 0 Mar 15 2002 scd0 brw-rw---- 1 root cdrom 11, 1 Mar 15 2002 scd1 brw-rw---- 1 root disk 8, 0 Mar 15 2002 sda brw-rw---- 1 root disk 8, 1 Mar 15 2002 sda1 brw-rw---- 1 root disk 8, 2 Mar 15 2002 sda2 brw-rw---- 1 root disk 8, 3 Mar 15 2002 sda3 brw-rw---- 1 root disk 8, 4 Mar 15 2002 sda4 brw-rw---- 1 root disk 8, 16 Mar 15 2002 sdb brw-rw---- 1 root disk 8, 17 Mar 15 2002 sdb1 brw-rw---- 1 root disk 8, 18 Mar 15 2002 sdb2 brw-rw---- 1 root disk 8, 19 Mar 15 2002 sdb3 brw-rw---- 1 root disk 8, 20 Mar 15 2002 sdb4 crw-rw---- 1 root audio 14, 1 Oct 7 16:26 sequencer lrwxrwxrwx 1 root root 10 Oct 7 16:26 sequencer2 -> /dev/music lrwxrwxrwx 1 root root 4 Sep 28 18:05 stderr -> fd/2 lrwxrwxrwx 1 root root 4 Sep 28 18:05 stdin -> fd/0 lrwxrwxrwx 1 root root 4 Sep 28 18:05 stdout -> fd/1 crw-rw-rw- 1 root tty 5, 0 Sep 28 18:06 tty crw------- 1 root root 4, 0 Sep 28 18:06 tty0 crw------- 1 root root 4, 1 Jan 19 14:59 tty1 crw-rw---- 1 root dialout 62, 64 Oct 7 06:50 ttyLT0 crw-rw---- 1 root dialout 4, 64 Mar 15 2002 ttyS0 crw-rw---- 1 root dialout 4, 65 Mar 15 2002 ttyS1 crw-rw---- 1 root dialout 4, 66 Mar 15 2002 ttyS2 crw-rw---- 1 root dialout 4, 67 Mar 15 2002 ttyS3 crw-rw---- 1 root dialout 188, 0 Mar 15 2002 ttyUSB0 crw-rw---- 1 root dialout 188, 1 Mar 15 2002 ttyUSB1 cr--r--r-- 1 root root 1, 9 Jan 19 20:46 urandom drwxr-xr-x 2 root root 4096 Sep 28 18:05 usb prw-r----- 1 root adm 0 Jan 19 14:58 xconsole crw-rw-rw- 1 root root 1, 5 Sep 28 18:06 zero Some common device files as well as their equivalent counterparts under Windows that you may wish to remember are: /dev/ttyS0 (First communications port, COM1) First serial port (mice, modems). /dev/psaux (PS/2) PS/2 mouse connection (mice, keyboards). /dev/lp0 (First printer port, LPT1) First parallel port (printers, scanners, etc). /dev/dsp (First audio device) The name DSP comes from the term digital signal processor, a specialized processor chip optimized for digital signal analysis. Sound cards may use a dedicated DSP chip, or may implement the functions with a number of discrete devices. Other terms that may be used for this device are digitized voice and PCM. /dev/usb (USB Devices) This subdirectory contains most of the USB device nodes. Device name allocations are fairly simplistic so no elaboration is be necessary. /dev/sda (C:\, SCSI device) First SCSI device (HDD, Memory Sticks, external mass storage devices such as CD-ROM drives on laptops, etc). /dev/scd (D:\, SCSI CD-ROM device) First SCSI CD-ROM device. /dev/js0 (Standard gameport joystick) First joystick device. Devices are defined by type, such as 'block' or 'character', and 'major' and 'minor' number. The major number is used to categorize a device and the minor number is used to identify a specific device type. For example, all IDE device connected to the primary controller have a major number of 3. Master and slave devices, as well as individual partitions are further defined by the use of minor numbers. These are the two numbers precede the date in the following display: # ls -l /dev/hd* brw-rw---- 1 root disk 3, 0 Mar 15 2002 /dev/hda brw-rw---- 1 root disk 3, 1 Mar 15 2002 /dev/hda1 brw-rw---- 1 root disk 3, 10 Mar 15 2002 /dev/hda10 brw-rw---- 1 root disk 3, 11 Mar 15 2002 /dev/hda11 brw-rw---- 1 root disk 3, 12 Mar 15 2002 /dev/hda12 brw-rw---- 1 root disk 3, 13 Mar 15 2002 /dev/hda13 brw-rw---- 1 root disk 3, 14 Mar 15 2002 /dev/hda14 brw-rw---- 1 root disk 3, 15 Mar 15 2002 /dev/hda15 brw-rw---- 1 root disk 3, 16 Mar 15 2002 /dev/hda16 brw-rw---- 1 root disk 3, 17 Mar 15 2002 /dev/hda17 brw-rw---- 1 root disk 3, 18 Mar 15 2002 /dev/hda18 brw-rw---- 1 root disk 3, 19 Mar 15 2002 /dev/hda19 brw-rw---- 1 root disk 3, 2 Mar 15 2002 /dev/hda2 brw-rw---- 1 root disk 3, 20 Mar 15 2002 /dev/hda20 brw-rw---- 1 root disk 3, 3 Mar 15 2002 /dev/hda3 brw-rw---- 1 root disk 3, 4 Mar 15 2002 /dev/hda4 brw-rw---- 1 root disk 3, 5 Mar 15 2002 /dev/hda5 brw-rw---- 1 root disk 3, 6 Mar 15 2002 /dev/hda6 brw-rw---- 1 root disk 3, 7 Mar 15 2002 /dev/hda7 brw-rw---- 1 root disk 3, 8 Mar 15 2002 /dev/hda8 brw-rw---- 1 root disk 3, 9 Mar 15 2002 /dev/hda9 brw-rw---- 1 root disk 3, 64 Mar 15 2002 /dev/hdb brw-rw---- 1 root disk 3, 65 Mar 15 2002 /dev/hdb1 brw-rw---- 1 root disk 3, 74 Mar 15 2002 /dev/hdb10 brw-rw---- 1 root disk 3, 75 Mar 15 2002 /dev/hdb11 brw-rw---- 1 root disk 3, 76 Mar 15 2002 /dev/hdb12 brw-rw---- 1 root disk 3, 77 Mar 15 2002 /dev/hdb13 brw-rw---- 1 root disk 3, 78 Mar 15 2002 /dev/hdb14 brw-rw---- 1 root disk 3, 79 Mar 15 2002 /dev/hdb15 brw-rw---- 1 root disk 3, 80 Mar 15 2002 /dev/hdb16 brw-rw---- 1 root disk 3, 81 Mar 15 2002 /dev/hdb17 brw-rw---- 1 root disk 3, 82 Mar 15 2002 /dev/hdb18 brw-rw---- 1 root disk 3, 83 Mar 15 2002 /dev/hdb19 brw-rw---- 1 root disk 3, 66 Mar 15 2002 /dev/hdb2 brw-rw---- 1 root disk 3, 84 Mar 15 2002 /dev/hdb20 brw-rw---- 1 root disk 3, 67 Mar 15 2002 /dev/hdb3 brw-rw---- 1 root disk 3, 68 Mar 15 2002 /dev/hdb4 brw-rw---- 1 root disk 3, 69 Mar 15 2002 /dev/hdb5 brw-rw---- 1 root disk 3, 70 Mar 15 2002 /dev/hdb6 brw-rw---- 1 root disk 3, 71 Mar 15 2002 /dev/hdb7 brw-rw---- 1 root disk 3, 72 Mar 15 2002 /dev/hdb8 brw-rw---- 1 root disk 3, 73 Mar 15 2002 /dev/hdb9 brw-rw---- 1 root disk 22, 0 Mar 15 2002 /dev/hdc brw-rw---- 1 root disk 22, 64 Mar 15 2002 /dev/hdd The major number for both hda and hdb devices is 3. Of course, the minor number changes for each specific partition. The definition of each major number category can be examined by looking at the contents of the /usr/src/ linux/include/linux/major.h file. The devices.txt also documents major and minor numbers. It is located in the /usr/src/linux/Documentation directory. This file defines the major numbers. Almost all files devices are created by default at the install time. However, you can always create a device using the mknod command or the MAKEDEV script which is located in the /dev directory itself. Devices can be created with this utility by supplying the device to be created, the device type (block or character) and the major and minor numbers. For example, let's say you have accidentally deleted /dev/ ttyS0 (COM1 under Windows), it can be recreated using the following command # mknod ttyS0 c 4 64 For those of us who are rather lazy you can simply run the MAKEDEV script as such # MAKEDEV * which will create all devices known. If is possible that /dev may also contain a MAKEDEV.local for the creation of any local device files. In general and as required by the FSSTND, MAKEDEV will have provisions for creating any device that may be found on the system, not just those that a particular implementation installs. For those of you who are wondering why Linux is using such a primitive system to reference devices its because we haven't been able to devise a sufficiently sophisticated mechanism which provides enough advantages over the current system in order to achieve widespread adoption. To date (as of kernel version 2.4), the best attempt has been made by Richard Gooch of the CSIRO. It's called devfsd and has been a part of the kernel for a number of years now. It has been sanctioned by the kernel developers and Linus himself and details of its implementation can be found at /usr/src/ linux/Documentation/filesystems/devfs/README. Below is an excerpt from this document. Devfs is an alternative to "real" character and block special devices on your root filesystem. Kernel device drivers can register devices by name rather than major and minor numbers. These devices will appear in devfs automatically, with whatever default ownership and protection the driver specified. A daemon (devfsd) can be used to override these defaults. Devfs has been in the kernel since 2.3.46. NOTE that devfs is entirely optional. If you prefer the old disc-based device nodes, then simply leave CONFIG_DEVFS_FS=n (the default). In this case, nothing will change. ALSO NOTE that if you do enable devfs, the defaults are such that full compatibility is maintained with the old devices names. There are two aspects to devfs: one is the underlying device namespace, which is a namespace just like any mounted filesystem. The other aspect is the filesystem code which provides a view of the device namespace. The reason I make a distinction is because devfs can be mounted many times, with each mount showing the same device namespace. Changes made are global to all mounted devfs filesystems. Also, because the devfs namespace exists without any devfs mounts, you can easily mount the root filesystem by referring to an entry in the devfs namespace. The cost of devfs is a small increase in kernel code size and memory usage. About 7 pages of code (some of that in __init sections) and 72 bytes for each entry in the namespace. A modest system has only a couple of hundred device entries, so this costs a few more pages. Compare this with the suggestion to put /dev on a ramdisc. On a typical machine, the cost is under 0.2 percent. On a modest system with 64 MBytes of RAM, the cost is under 0.1 percent. The accusations of "bloatware" levelled at devfs are not justified. As of kernel version 2.6, devfs has been marked obsolete and has now been replaced by udev. A system very similar (at least from a the end user's point of view) to devfs but which works entirely in userspace. An overview of udev can be found at [http://www.kroah.com/linux/talks/ols_2003_udev_paper/ Reprint-Kroah-Hartman-OLS2003.pdf] http://www.kroah.com/linux/talks/ ols_2003_udev_paper/Reprint-Kroah-Hartman-OLS2003.pdf ----------------------------------------------------------------------------- 1.6. /etc This is the nerve center of your system, it contains all system related configuration files in here or in its sub-directories. A "configuration file" is defined as a local file used to control the operation of a program; it must be static and cannot be an executable binary. For this reason, it's a good idea to backup this directory regularly. It will definitely save you a lot of re-configuration later if you re-install or lose your current installation. Normally, no binaries should be or are located here. /etc/X11/ This directory tree contains all the configuration files for the X Window System. Users should note that many of the files located in this directory are actually symbolic links to the /usr/X11R6 directory tree. Thus, the presence of these files in these locations can not be certain. /etc/X11/XF86Config, /etc/X11/XF86Config-4 The 'X' configuration file. Most modern distributions possess hardware autodetection systems that enable automatic creation of a valid file. Should autodetection fail a configuration file can also be created manually provided that you have sufficient knowledge about your system. It would be considered prudent not to attempt to type out a file from beginning to end. Rather, use common configuration utilities such as xf86config, XF86Setup and xf86cfg to create a workable template. Then, using suitable documentation commence optimization through intuition and/ or trial and error. Options that can be configured via this file include X modules to be loaded on startup, keyboard, mouse, monitor and graphic chipset type. Often, commercial distributions will include their own X configuration utilities such as XDrake on Mandrake and also Xconfiguration on Redhat. Below is a sample X configuration file from the reference system ### BEGIN DEBCONF SECTION # XF86Config-4 (XFree86 server configuration file) generated by dexconf, the # Debian X Configuration tool, using values from the debconf database. # # Edit this file with caution, and see the XF86Config-4 manual page. # (Type "man XF86Config-4" at the shell prompt.) # # If you want your changes to this file preserved by dexconf, only # make changes # before the "### BEGIN DEBCONF SECTION" line above, and/or after the # "### END DEBCONF SECTION" line below. # # To change things within the debconf section, run the command: # dpkg-reconfigure xserver-xfree86 # as root. Also see "How do I add custom sections to a dexconf- # generated # XF86Config or XF86Config-4 file?" in /usr/share/doc/xfree86- # common/FAQ.gz. Section "Files" FontPath "unix/:7100" # local font server # if the local font server has problems, # we can fall back on these FontPath "/usr/lib/X11/fonts/misc" FontPath "/usr/lib/X11/fonts/cyrillic" FontPath "/usr/lib/X11/fonts/100dpi/:unscaled" FontPath "/usr/lib/X11/fonts/75dpi/:unscaled" FontPath "/usr/lib/X11/fonts/Type1" FontPath "/usr/lib/X11/fonts/Speedo" FontPath "/usr/lib/X11/fonts/100dpi" FontPath "/usr/lib/X11/fonts/75dpi" EndSection Section "Module" Load "GLcore" Load "bitmap" Load "dbe" Load "ddc" Load "dri" Load "extmod" Load "freetype" Load "glx" Load "int10" Load "pex5" Load "record" Load "speedo" Load "type1" Load "vbe" Load "xie" EndSection Section "InputDevice" Identifier "Generic Keyboard" Driver "keyboard" Option "CoreKeyboard" Option "XkbRules" "xfree86" Option "XkbModel" "pc104" Option "XkbLayout" "us" EndSection Section "InputDevice" Identifier "Configured Mouse" Driver "mouse" Option "CorePointer" Option "Device" "/dev/psaux" Option "Protocol" "NetMousePS/2" Option "Emulate3Buttons" "true" Option "ZAxisMapping" "4 5" EndSection Section "InputDevice" Identifier "Generic Mouse" Driver "mouse" Option "SendCoreEvents" "true" Option "Device" "/dev/input/mice" Option "Protocol" "ImPS/2" Option "Emulate3Buttons" "true" Option "ZAxisMapping" "4 5" EndSection Section "Device" Identifier "Generic Video Card" Driver "nv" # Option "UseFBDev" "true" Option "UseFBDev" "false" EndSection Section "Monitor" Identifier "Generic Monitor" HorizSync 30-38 VertRefresh 43-95 Option "DPMS" EndSection Section "Screen" Identifier "Default Screen" Device "Generic Video Card" Monitor "Generic Monitor" DefaultDepth 16 SubSection "Display" Depth 1 Modes "800x600" "640x480" EndSubSection SubSection "Display" Depth 4 Modes "800x600" "640x480" EndSubSection SubSection "Display" Depth 8 Modes "800x600" "640x480" EndSubSection SubSection "Display" Depth 15 Modes "800x600" "640x480" EndSubSection SubSection "Display" Depth 16 Modes "800x600" "640x480" EndSubSection SubSection "Display" Depth 24 Modes "800x600" "640x480" EndSubSection EndSection Section "ServerLayout" Identifier "Default Layout" Screen "Default Screen" InputDevice "Generic Keyboard" InputDevice "Configured Mouse" InputDevice "Generic Mouse" EndSection Section "DRI" Mode 0666 EndSection ### END DEBCONF SECTION As you can see, the layout of the file is quite simple and tends to be quite standard across most distributions. At the top are the locations of the various font files for X (note - X will not start if you do not specify a valid font), next is the "Modules" section. It details what modules are to be loaded upon startup. The most well known extensions are probably GLX (required for 3D rendering of graphics and games) and Xinerama which allows users to expand their desktop over several monitors. Next are the various "Device" sections which describe the type of hardware you have. Improper configuration of these subsections can lead to heartache and trauma with seemingly misplaced keys, bewitched mice and also constant flashing as X attempts to restart in a sometimes never ending loop. In most cases when all else fails the vesa driver seems to be able to initialise most modern video cards. In the "Screen" section it is possible to alter the default startup resolution and depth. Quite often it is possible to alter these attributes on the fly by using the alt-ctrl-+ or alt-ctrl- set of keystrokes. Lastly are the "ServerLayout" and "DRI" sections. Users will almost never touch the "DRI" section and only those who wish to utilise the Xinerama extensions of X will require having to change any of the ServerLayout options. /etc/X11/Xmodmap In general your default keyboard mapping comes from your X server setup. If this setup is insufficient and you are unwilling to go through the process of reconfiguration and/or you are not the superuser you'll need to use the xmodmap program. This is the utility's global configuration file. /etc/X11/xkb/ The various symbols, types, geometries of keymaps that the X server supports can be found in this directory tree. /etc/X11/lbxproxy/ Low Bandwidth X (LBX) proxy server configuration files. Applications that would like to take advantage of the Low Bandwidth extension to X (LBX) must make their connections to an lbxproxy. These applications need know nothing about LBX, they simply connect to the lbxproxy as if it were a regular X server. The lbxproxy accepts client connections, multiplexes them over a single connection to the X server, and performs various optimizations on the X protocol to make it faster over low bandwidth and/ or high latency connections. It should be noted that such compression will not increase the pace of rendering all that much. Its primary purpose is to reduce network load and thus increase overall network latency. A competing project called DXPC (Differential X Protocol Compression) has been found to be more efficient at this task. Studies have shown though that in almost all cases ssh tunneling of X will produce far better results than through any of these specialised pieces of software. /etc/X11/proxymngr/ X proxy services manager initialisation files. proxymngr is responsible for resolving requests from xfindproxy (in the xbase-clients package) and other similar clients, starting new proxies when appropriate, and keeping track of all the available proxy services. /etc/X11/xdm/ X display manager configuration files. xdm manages a collection of X servers, which may be on the local host or remote machines. It provides services similar to those provided by init, getty, and login on character-based terminals: prompting for login name and password, authenticating the user, and running a session. xdm supports XDMCP (X Display Manager Control Protocol) and can also be used to run a chooser process which presents the user with a menu of possible hosts that offer XDMCP display management. If the xutils package is installed, xdm can use the sessreg utility to register login sessions to the system utmp file; this, however, is not necessary for xdm to function. /etc/X11/xdm/xdm-config This is the master 'xdm' configuration file. It determines where all other 'xdm' configuration files will be located. It is almost certain to be left undisturbed. /etc/X11/gdm/ GNOME Display Manager configuration files. gdm provides the equivalent of a "login:" prompt for X displays- it pops up a login window and starts an X session. It provides all the functionality of xdm, including XDMCP support for managing remote displays. The greeting window is written using the GNOME libraries and hence looks like a GNOME application- even to the extent of supporting themes! By default, the greeter is run as an unprivileged user for security. /etc/X11/gdm/gdm.conf This is the primary configuration file for GDM. Through it, users can specify whether they would like their system to automatically login as a certain user, background startup image and also if they would like to run their machine as somewhat of a terminal server by using the XDMCP protocol. /etc/X11/fonts Home of xfs fonts. /etc/X11/fs/ X font server configuration files. xfs is a daemon that listens on a network port and serves X fonts to X servers (and thus to X clients). All X servers have the ability to serve locally installed fonts for themselves, but xfs makes it possible to offload that job from the X server, and/or have a central repository of fonts on a networked machine running xfs so that all the machines running X servers on a network do not require their own set of fonts. xfs may also be invoked by users to, for instance, make available X fonts in user accounts that are not available to the X server or to an already running system xfs. /etc/X11/fs/config This is the 'xfs' initialisation file. It specifies the number of clients that are allowed to connect to the 'xfs' server at any one time, the location of log files, default resolution, the location of the fonts, etc. # font server configuration file # $Xorg: config.cpp,v 1.3 2000/08/17 19:54:19 cpqbld Exp $ # allow a maximum of 10 clients to connect to this font server client-limit = 10 # when a font server reaches its limit, start up a new one clone-self = on # log messages to /var/log/xfs.log (if syslog is not used) error-file = /var/log/xfs.log # log errors using syslog use-syslog = on # turn off TCP port listening (Unix domain connections are still permitted) no-listen = tcp # paths to search for fonts catalogue = /usr/lib/X11/fonts/misc/,/usr/lib/X11/fonts/cyrillic/, /usr/lib/X11/fonts/100dpi/:unscaled,/usr/lib/X11/fonts/75dpi/:unscaled, /usr/lib/X11/fonts/Type1/,/usr/lib/X11/fonts/CID, /usr/lib/X11/fonts/Speedo/,/usr/lib/X11/fonts/100dpi/, /usr/lib/X11/fonts/75dpi/ # in decipoints default-point-size = 120 # x1,y1,x2,y2,... default-resolutions = 100,100,75,75 # font cache control, specified in kB cache-hi-mark = 2048 cache-low-mark = 1433 cache-balance = 70 /etc/X11/twm Home of configuration files for twm. The original Tabbed Window Manager. /etc/X11/xinit/ xinit configuration files. 'xinit' is a configuration method of starting up an X session that is designed to used as part of a script. Normally, this is used at larger sites as part of a tailored login process. /etc/X11/xinit/xinitrc Global xinitrc file, used by all X sessions started by xinit (startx). Its usage is of course overridden by a .xinitrc file located in the home directory of a user. /etc/adduser.conf 'adduser' configuration. The adduser command can create new users, groups and add existing users to existing groups. Adding users with adduser is much easier than adding them by hand. Adduser will choose appropriate UID and GID values, create a home directory, copy skeletal user configuration from /etc/skel, allow you to set an initial password and the GECOS field. Optionally a custom script can be executed after this commands. See adduser(8) and adduser.conf(5) for full documentation. /etc/adjtime Has parameters to help adjust the software (kernel) time so that it matches the RTC. /etc/aliases This is the aliases file - it says who gets mail for whom. It was originally generated by `eximconfig', part of the exim package distributed with Debian, but it may edited by the mail system administrator. See exim info section for details of the things that can be configured here. An aliases database file (aliases.db) is built from the entries in the aliases files by the newaliases utility. /etc/alternatives It is possible for several programs fulfilling the same or similar functions to be installed on a single system at the same time. For example, many systems have several text editors installed at once. This gives choice to the users of a system, allowing each to use a different editor, if desired, but makes it difficult for a program to make a good choice of editor to invoke if the user has not specified a particular preference. The alternatives system aims to solve this problem. A generic name in the filesystem is shared by all files providing interchangeable functionality. The alternatives system and the system administrator together determine which actual file is referenced by this generic name. For example, if the text editors ed(1) and nvi(1) are both installed on the system, the alternatives system will cause the generic name /usr/bin/ editor to refer to /usr/bin/nvi by default. The system administrator can override this and cause it to refer to /usr/bin/ed instead, and the alternatives system will not alter this setting until explicitly requested to do so. The generic name is not a direct symbolic link to the selected alternative. Instead, it is a symbolic link to a name in the alternatives directory, which in turn is a symbolic link to the actual file referenced. This is done so that the system administrator's changes can be confined within the /etc directory. /etc/apt This is Debian's next generation front-end for the dpkg package manager. It provides the apt-get utility and APT dselect method that provides a simpler, safer way to install and upgrade packages. APT features complete installation ordering, multiple source capability and several other unique features, see the Users Guide in /usr/share/doc/apt/guide.text.gz /etc/apt/sources.list deb cdrom:[Debian GNU/Linux 3.0 r0 _Woody_ - Official i386 Binary-7 (20020718)]/ unstable contrib main non-US/contrib non-US/main deb cdrom:[Debian GNU/Linux 3.0 r0 _Woody_ - Official i386 Binary-6 (20020718)]/ unstable contrib main non-US/contrib non-US/main deb cdrom:[Debian GNU/Linux 3.0 r0 _Woody_ - Official i386 Binary-5 (20020718)]/ unstable contrib main non-US/contrib non-US/main deb cdrom:[Debian GNU/Linux 3.0 r0 _Woody_ - Official i386 Binary-4 (20020718)]/ unstable contrib main non-US/contrib non-US/main deb cdrom:[Debian GNU/Linux 3.0 r0 _Woody_ - Official i386 Binary-3 (20020718)]/ unstable contrib main non-US/contrib non-US/main deb cdrom:[Debian GNU/Linux 3.0 r0 _Woody_ - Official i386 Binary-2 (20020718)]/ unstable contrib main non-US/contrib non-US/main deb cdrom:[Debian GNU/Linux 3.0 r0 _Woody_ - Official i386 Binary-1 (20020718)]/ unstable contrib main non-US/contrib non-US/main # deb http://security.debian.org/ stable/updates main Contains a list of apt-sources from which packages may be installed via APT. /etc/asound.conf ALSA (Advanced Linux Sound Architecture) configuration file. It is normally created via alsactl or other third-party sound configuration utilities that may be specific to a distribution such as sndconfig from Redhat. /etc/at.deny Users denied access to the at daemon. The 'at' command allows user to execute programs at an arbitrary time. /etc/autoconf Configuration files for autoconf. 'autoconf' creates scripts to configure source code packages using templates. To create configure from configure.in, run the autoconf program with no arguments. autoconf processes configure.ac with the m4 macro processor, using the Autoconf macros. If you give autoconf an argument, it reads that file instead of configure.ac and writes the configuration script to the standard output instead of to configure. If you give autoconf the argument -, it reads the standard input instead of configure.ac and writes the configuration script on the standard output. The Autoconf macros are defined in several files. Some of the files are distributed with Autoconf; autoconf reads them first. Then it looks for the optional file acsite.m4 in the directory that contains the distributed Autoconf macro files, and for the optional file aclocal.m4 in the current directory. Those files can contain your site's or the package's own Autoconf macro definitions. If a macro is defined in more than one of the files that autoconf reads, the last definition it reads overrides the earlier ones. /etc/bash.bashrc System wide functions and aliases' file for interactive bash shells. /etc/bash_completion Programmable completion functions for bash 2.05a. /etc/chatscripts/provider This is the chat script used to dial out to your default service provider. /etc/cron.d, /etc/cron.daily, /etc/cron.weekly, /etc/cron.monthly These directories contain scripts to be executed on a regular basis by the cron daemon. /etc/crontab 'cron' configuration file. This file is for the cron table to setup the automatic running of system routines. A cron table can also be established for individual users. The location of these user cron table files will be explained later on. # /etc/crontab: system-wide crontab # Unlike any other crontab you don't have to run the `crontab' # command to install the new version when you edit this file. # This file also has a username field, that none of the other crontabs do. SHELL=/bin/sh PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin # m h dom mon dow user command 25 6 * * * root test -e /usr/sbin/anacron || run-parts --report /etc/cron.daily 47 6 * * 7 root test -e /usr/sbin/anacron || run-parts --report /etc/cron.weekly 52 6 1 * * root test -e /usr/sbin/anacron || run-parts --report /etc/cron.monthly # /etc/csh.login System-wide .login file for csh(1). This file is sourced on all invocations of the shell. It contains commands that are to be executed upon login and sometimes aliases also. /etc/csh.logout System-wide .logout file for csh(1). This file is sourced on all invocations of the shell. It contains commands that are to be executed upon logout. /etc/csh.cshrc System-wide .cshrc file for csh(1). This file is sourced on all invocations of the shell. This file should contain commands to set the command search path, plus other important environment variables. This file should not contain commands that produce output or assume the shell is attached to a tty. /etc/cups Configuration files for the Common UNIX Printing System (CUPS). Files here are used to define client-specific parameters, such as the default server or default encryption settings. /etc/deluser.conf 'deluser' configuration files. The deluser command can remove users and groups and remove users from a given group. Deluser can optionally remove and backup the user's home directory and mail spool or all files on the system owned by him. Optionally a custom script can also be executed after each of the commands. /etc/devfs This daemon sets up the /dev filesystem for use. It creates required symbolic links in /dev and also creates (if so configured, as is the default) symbolic links to the "old" names for devices. /etc/devfs/conf.d/ 'devfsd' configuration files. This daemon sets up the /dev filesystem for use. It creates required symbolic links in /dev and also creates (if so configured, as is the default) symbolic links to the "old" names for devices. /etc/dhclient.conf, /etc/dhclient-script 'dhclient' configuration file and 'dhclient' script files respectively. It configures your system so that it may act as a client on a DHCP based network. It is essential to connect to the Internet nowadays. /etc/dict.conf # /etc/dict.conf Written by Bob Hilliard # 1998/03/20. Last revised Sun, 22 Nov 1998 18:10:04 -0500 This is # the configuration file for /usr/bin/dict. In most cases only the # server keyword need be specified. # This default configuration will try to access a dictd server on # the local host, failing that, it will try the public server. In # many cases this will be slow, so you should comment out the line # for the server that you don't want to use. To use any other # server, enter its IP address in place of "dict.org". # Refer to the dict manpage (man dict) for other options that could # be inserted in here. server localhost server dict.org dict is a client for the Dictionary Server Protocol (DICT), a TCP transaction based query/response protocol that provides access to dictionary definitions from a set of natural language dictionary databases. /etc/dosemu.conf Configuration file for the Linux DOS Emulator. DOSEMU is a PC Emulator application that allows Linux to run a DOS operating system in a virtual x86 machine. This allows you to run many DOS applications. It includes the FreeDOS kernel, color text and full keyboard emulation (via hotkeys) via terminal, built-in X support, IBM character set font, graphics capability at the console with most compatible video cards, DPMI support so you can run DOOM, CDROM support, builtin IPX and pktdrvr support. Note - 'dosemu' is simply a ported version of Corel's own PC-DOS. /etc/email-addresses Part of the exim package. This file contains email addresses to use for outgoing mail. Any local part not in here will be qualified by the system domain as normal. It should contain lines of the form: user: someone@isp.com otheruser: someoneelse@anotherisp.com Exim is an MTA that is considered to be rather easier to configure than smail or sendmail. It is a drop-in replacement for sendmail, mailq and rsmtp. Advanced features include the ability to reject connections from known spam sites, and an extremely efficient queue processing algorithm. /etc/esound.conf ESD configuration files. The Enlightened sound daemon is designed to mix together several digitized audio streams for playback by a single device. Like nasd, artsd and rplay it also has the capability to play sounds remotely. /etc/exports The control list of systems who want to access the system via NFS, a the list of directories that you would like to share and the permissions allocated on each share. # /etc/exports: the access control list for filesystems which may be # exported to NFS clients. See exports(5). ## LTS-begin ## # # The lines between the 'LTS-begin' and the 'LTS-end' were added # on: Sun Feb 23 05:54:17 EST 2003 by the ltsp installation script. # For more information, visit the ltsp homepage # at http://www.ltsp.org # /opt/ltsp/i386 192.168.0.0/255.255.255.0(ro,no_root_squash) /var/opt/ltsp/swapfiles 192.168.0.0/255.255.255.0(rw,no_root_squash) # # The following entries need to be uncommented if you want # Local App support in ltsp # #/home 192.168.0.0/255.255.255.0(rw,no_root_squash) ## LTS-end ## /etc/fdprm Floppy disk parameter table. Describes what different floppy disk formats look like. Used by setfdprm. /etc/fstab The configuration file for 'mount' and now 'supermount'. It lists the filesystems mounted automatically at startup by the mount -a command (in /etc/rc or equivalent startup file). Under Linux, also contains information about swap areas used automatically by swapon -a. # /etc/fstab: static file system information. # # The following is an example. Please see fstab(5) for further details. # Please refer to mount(1) for a complete description of mount options. # # Format: # # # dump(8) uses the field to determine which file systems need # to be dumped. fsck(8) uses the column to determine which file # systems need to be checked--the root file system should have a 1 in # this field, other file systems a 2, and any file systems that should # not be checked (such as MS-DOS or NFS file systems) a 0. # # The `sw' option indicates that the swap partition is to be activated # with `swapon -a'. /dev/hda2 none swap sw 0 0 # The `bsdgroups' option indicates that the file system is to be mounted # with BSD semantics (files inherit the group ownership of the directory # in which they live). `ro' can be used to mount a file system read-only. /dev/hda3 / ext2 defaults 0 1 /dev/hda5 /home ext2 defaults 0 2 /dev/hda6 /var ext2 defaults 0 2 /dev/hda7 /usr ext2 defaults,ro 0 2 /dev/hda8 /usr/local ext2 defaults,bsdgroups 0 2 # The `noauto' option indicates that the file system should not be mounted # with `mount -a'. `user' indicates that normal users are allowed to mount # the file system. /dev/cdrom /cdrom iso9660 defaults,noauto,ro,user 0 0 /dev/fd0 /floppy minix defaults,noauto,user 0 0 /dev/fd1 /floppy minix defaults,noauto,user 0 0 # NFS file systems: server: /export/usr /usr nfs defaults 0 0 # proc file system: proc /proc proc defaults 0 0 /etc/ftpaccess Determines who might get ftp-access to your machine. /etc/ftpchroot List of ftp users that need to be chrooted. /etc/ftpuser List of disallowed ftp users. /etc/gateways Lists gateways for 'routed'. /etc/gettydefs Configures console-logins. /etc/gnome-vfs-mime-magic MIME magic patterns as used by the Gnome VFS library. /etc/group Similar to /etc/passwd. It lists the configured user groups and who belongs to them. /etc/group- Old /etc/group file. /etc/gshadow Contains encrypted forms of group passwords. /etc/gshadow- Old /etc/gshadow file. /etc/hostname Contains the hostname of your machine (can be fully qualified or not). /etc/host.conf Determines the search order for look-ups (usually hosts bind, i.e. "check /etc/hosts first and then look for a DNS"). /etc/hosts This file is used to define a system name and domain combination with a specific IP address. This file needs to always contain an entry for an IP address, if the machine is connected to the network. ### etherconf DEBCONF AREA. DO NOT EDIT THIS AREA OR INSERT TEXT BEFORE IT. 127.0.0.1 localhost ::1 localhost ip6-localhost ip6-loopback fe00::0 ip6-localnet ff00::0 ip6-mcastprefix ff02::1 ip6-allnodes ff02::2 ip6-allrouters ff02::3 ip6-allhosts 192.168.0.99 debian.localdomain.com debian ### END OF DEBCONF AREA. PLACE YOUR EDITS BELOW; THEY WILL BE PRESERVED. 192.168.0.1 ws001 /etc/hosts.allow Part of the tcp-wrappers system to control access to your machine's services. It lists hosts that are allowed to access the system and specific daemons. # /etc/hosts.allow: list of hosts that are allowed to access the # system. # See the manual pages hosts_access(5), hosts_options(5) # and /usr/doc/netbase/portmapper.txt.gz # # Example: ALL: LOCAL @some_netgroup # ALL: .foobar.edu EXCEPT terminalserver.foobar.edu # # If you're going to protect the portmapper use the name "portmap" # for the daemon name. Remember that you can only use the keyword # "ALL" and IP addresses (NOT host or domain names) for the # portmapper. See portmap(8) and /usr/doc/portmap/portmapper.txt.gz # for further information. bootpd: 0.0.0.0 in.tftpd: 192.168.0. portmap: 192.168.0. rpc.mountd: 192.168.0. rpc.nfsd: 192.168.0. gdm: 192.168.0. nasd: 192.168.0. /etc/hosts.deny part of the tcp-wrappers system to control access to your machine's services. It lists hosts that are not allowed to access the system. # Example: ALL: some.host.name, .some.domain # ALL EXCEPT in.fingerd: other.host.name, .other.domain # # If you're going to protect the portmapper use the name "portmap" # for the daemon name. Remember that you can only use the keyword # "ALL" and IP addresses (NOT host or domain names) for the # portmapper. See portmap(8) and /usr/doc/portmap/portmapper.txt.gz # for further information. # # The PARANOID wildcard matches any host whose name does not match # its address. You may wish to enable this to ensure any programs # that don't validate looked up hostnames still leave understandable # logs. In past versions of Debian this has been the default. # ALL: PARANOID /etc/httpd Apache configuration files. Apache is a versatile, high-performance HTTP server. The most popular server in the world, Apache features a modular design and supports dynamic selection of extension modules at runtime. Its strong points are its range of possible customization, dynamic adjustment of the number of server processes, and a whole range of available modules including many authentication mechanisms, server-parsed HTML, server-side includes, access control, CERN httpd metafiles emulation, proxy caching, etc. Apache also supports multiple virtual homing. /etc/identd.conf TCP/IP IDENT protocol server. It implements the TCP/IP proposed standard IDENT user identification protocol (RFC 1413). identd operates by looking up specific TCP/IP connections and returning the username of the process owning the connection. It can also return other information besides the username. # /etc/identd.conf - an example configuration file #-- The syslog facility for error messages # syslog:facility = daemon #-- User and group (from passwd database) to run as server:user = nobody #-- Override the group id # server:group = kmem #-- What port to listen on when started as a daemon or from /etc/inittab # server:port = 113 #-- The socket backlog limit # server:backlog = 256 #-- Where to write the file containing our process id # server:pid-file = "/var/run/identd/identd.pid" #-- Maximum number of concurrent requests allowed (0 = unlimited) # server:max-requests = 0 #-- Enable some protocol extensions like "VERSION" or "QUIT" protocol:extensions = enabled #-- Allow multiple queries per connection protocol:multiquery = enabled #-- Timeout in seconds since connection or last query. Zero = disable # protocol:timeout = 120 #-- Maximum number of threads doing kernel lookups # kernel:threads = 8 #-- Maximum number of queued kernel lookup requests # kernel:buffers = 32 #-- Maximum number of time to retry a kernel lookup in case of failure # kernel:attempts = 5 #-- Disable username lookups (only return uid numbers) # result:uid-only = no #-- Enable the ".noident" file # result:noident = enabled #-- Charset token to return in replies # result:charset = "US-ASCII" #-- Opsys token to return in replies # result:opsys = "UNIX" #-- Log all request replies to syslog (none == don't) # result:syslog-level = none #-- Enable encryption (only available if linked with a DES library) # result:encrypt = no #-- Path to the DES key file (only available if linked with a DES library) # encrypt:key-file = "/usr/local/etc/identd.key" #-- Include a machine local configuration file # include = /etc/identd.conf /etc/inetd.conf Configuration of services that are started by the INETD TCP/IP super server. 'inetd' is now deprecated. 'xinetd' has taken its place. See /etc /xinet.conf for further details. # /etc/inetd.conf: see inetd(8) for further information. # # Internet server configuration database # # # Lines starting with "#:LABEL:" or "##" should not # be changed unless you know what you are doing! # # If you want to disable an entry so it isn't touched during # package updates just comment it out with a single '#' character. # # Packages should modify this file by using update-inetd(8) # # # # # #:INTERNAL: Internal services #echo stream tcp nowait root internal #echo dgram udp wait root internal #chargen stream tcp nowait root internal #chargen dgram udp wait root internal discard stream tcp nowait root internal discard dgram udp wait root internal daytime stream tcp nowait root internal #daytime dgram udp wait root internal time stream tcp nowait root internal #time dgram udp wait root internal #:STANDARD: These are standard services. ftp stream tcp nowait root /usr/sbin/tcpd /usr/sbin/in.ftpd telnet stream tcp nowait telnetd.telnetd /usr/sbin/tcpd /usr/sbin/in.telnetd #:MAIL: Mail, news and uucp services. smtp stream tcp nowait mail /usr/sbin/exim exim -bs imap2 stream tcp nowait root /usr/sbin/tcpd /usr/sbin/imapd imap3 stream tcp nowait root /usr/sbin/tcpd /usr/sbin/imapd #:INFO: Info services ident stream tcp wait identd /usr/sbin/identd identd finger stream tcp nowait nobody /usr/sbin/tcpd /usr/sbin/in.fingerd #:BOOT: Tftp service is provided primarily for booting. #Most sites run this only on machines acting as "boot servers." tftp dgram udp wait nobody /usr/sbin/tcpd /usr/sbin/in.tftpd -s /tftpboot /etc/init.d Order of scripts run in /etc/rc?.d ================================== 0. Overview. All scripts executed by the init system are located in /etc/init.d. The directories /etc/rc?.d (? = S, 0 .. 6) contain relative links to those scripts. These links are named S<2-digit-number>< original-name> or K<2-digit-number>. If a scripts has the ".sh" suffix it is a bourne shell script and MAY be handled in an optimized manner. The behaviour of executing the script in an optimized way will not differ in any way from it being forked and executed in the regular way. The following runlevels are defined: N System bootup (NONE). S Single user mode (not to be switched to directly) 0 halt 1 single user mode 2 .. 5 multi user mode 6 reboot 1. Boot. When the systems boots, the /etc/init.d/rcS script is executed. It in turn executes all the S* scripts in /etc/rcS.d in alphabetical (and thus numerical) order. The first argument passed to the executed scripts is "start". The runlevel at this point is "N" (none). Only things that need to be run once to get the system in a consistent state are to be run. The rcS.d directory is NOT meant to replace rc.local. One should not start daemons in this runlevel unless absolutely necessary. Eg, NFS might need the portmapper, so it is OK to start it early in the boot process. But this is not the time to start the squid proxy server. 2. Going multiuser. After the rcS.d scripts have been executed, init switches to the default runlevel as specified in /etc/inittab, usually "2". Init then executes the /etc/init.d/rc script which takes care of starting the services in /etc/rc2.d. Because the previous runlevel is "N" (none) the /etc/rc2.d/KXXxxxx scripts will NOT be executed - there is nothing to stop yet, the system is busy coming up. If for example there is a service that wants to run in runlevel 4 and ONLY in that level, it will place a KXXxxxx script in /etc/rc{2,3,5}.d to stop the service when switching out of runlevel 4. We do not need to run that script at this point. The /etc.rc2.d/SXXxxxx scripts will be executed in alphabetical order, with the first argument set to "start". 3. Switching runlevels. When one switches from (for example) runlevel 2 to runlevel 3, /etc/init.d/rc will first execute in alphabetical order all K scripts for runlevel 3 (/etc/rc3.d/KXXxxxx) with as first argument "stop" and then all S scripts for runlevel 3 (/etc/rc3.d/SXXxxxx) with as first argument "start". As an optimization, a check is made for each "service" to see if it was already running in the previous runlevel. If it was, and there is no K (stop) script present for it in the new runlevel, there is no need to start it a second time so that will not be done. On the other hand, if there was a K script present, it is assumed the service was stopped on purpose first and so needs to be restarted. We MIGHT make the same optimization for stop scripts as well- if no S script was present in the previous runlevel, we can assume that service was not running and we don't need to stop it either. In that case we can remove the "coming from level N" special case mentioned above in 2). But right now that has not been implemented. 4. Single user mode. Switching to single user mode is done by switching to runlevel 1. That will cause all services to be stopped (assuming they all have a K script in /etc/rc1.d). The runlevel 1 scripts will then switch to runlevel "S" which has no scripts - all it does is spawn a shell directly on /dev/console for maintenance. 5. Halt/reboot Going to runlevel 0 or 6 will cause the system to be halted or rebooted, respectively. For example, if we go to runlevel 6 (reboot) first all /etc/rc6.d/KXXxxxx scripts will be executed alphabetically with "stop" as the first argument. Then the /etc/rc6.d/SXXxxxx scripts will be executed alphabetically with "stop" as the first argument as well. The reason is that there is nothing to start any more at this point - all scripts that are run are meant to bring the system down. In the future, the /etc/rc6.d/SXXxxxx scripts MIGHT be moved to /etc/rc6.d/K1XXxxxx for clarity. /etc/inittab Boot-time system configuration/initialization script. Tells init how to handle runlevels. It sets the default runlevel. This is run first except when booting in emergency (-b) mode. It also enables a user to startup a getty session on an external device such as the serial ports. To add terminals or dial-in modem lines to a system, just add more lines to /etc /inittab, one for each terminal or dial-in line. For more details, see the manual pages init, inittab, and getty. If a command fails when it starts, and init is configured to restart it, it will use a lot of system resources: init starts it, it fails, init starts it, it fails, and so on. To prevent this, init will keep track of how often it restarts a command, and if the frequency grows to high, it will delay for five minutes before restarting again. /etc/inittab also has some special features that allow init to react to special circumstances. powerwait Allows init to shut the system down, when the power fails. This assumes the use of a UPS, and software that watches the UPS and informs init that the power is off. ctrlaltdel Allows init to reboot the system, when the user presses ctrl-alt-del on the console keyboard. Note that the system administrator can configure the reaction to ctrl-alt-del to be something else instead, e.g., to be ignored, if the system is in a public location. sysinit Command to be run when the system is booted. This command usually cleans up /tmp, for example. The list above is not exhaustive. See your inittab manual page for all possibilities, and for details on how to use the ones above. To set (or reset) initial terminal colours. The following shell script should work for VGA consoles: for n in 1 2 4 5 6 7 8; do setterm -fore yellow -bold on -back blue -store > /dev/tty$n done Substitute your favorite colors, and use /dev/ttyS$n for serial terminals. To make sure they are reset when people log out (if they've been changed) replace the references to getty (or mingetty or uugetty or whatever) in /etc/inittab with references to /sbin/mygetty. #!/bin/sh setterm -fore yellow -bold on -back blue -store > $1 exec /sbin/mingetty $@ An example /etc/inittab is provided below. # /etc/inittab: init(8) configuration. # $Id: etc.xml,v 1.10 2004/02/03 21:42:57 binh Exp $ # The default runlevel. id:2:initdefault: # Boot-time system configuration/initialization script. # This is run first except when booting in emergency (-b) mode. si::sysinit:/etc/init.d/rcS # What to do in single-user mode. ~~:S:wait:/sbin/sulogin # /etc/init.d executes the S and K scripts upon change # of runlevel. # # Runlevel 0 is halt. # Runlevel 1 is single-user. # Runlevels 2-5 are multi-user. # Runlevel 6 is reboot. l0:0:wait:/etc/init.d/rc 0 l1:1:wait:/etc/init.d/rc 1 l2:2:wait:/etc/init.d/rc 2 l3:3:wait:/etc/init.d/rc 3 l4:4:wait:/etc/init.d/rc 4 l5:5:wait:/etc/init.d/rc 5 l6:6:wait:/etc/init.d/rc 6 # Normally not reached, but fallthrough in case of emergency. z6:6:respawn:/sbin/sulogin # What to do when CTRL-ALT-DEL is pressed. ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -r now # Action on special keypress (ALT-UpArrow). #kb::kbrequest:/bin/echo "Keyboard Request #--edit /etc/inittab to let this work." # What to do when the power fails/returns. pf::powerwait:/etc/init.d/powerfail start pn::powerfailnow:/etc/init.d/powerfail now po::powerokwait:/etc/init.d/powerfail stop # /sbin/getty invocations for the runlevels. # # The "id" field MUST be the same as the last # characters of the device (after "tty"). # # Format: # ::: # # Note that on most Debian systems tty7 is used by the X Window System, # so if you want to add more getty's go ahead but skip tty7 if you run X. # 1:2345:respawn:/sbin/getty 38400 tty1 2:23:respawn:/sbin/getty 38400 tty2 3:23:respawn:/sbin/getty 38400 tty3 4:23:respawn:/sbin/getty 38400 tty4 5:23:respawn:/sbin/getty 38400 tty5 6:23:respawn:/sbin/getty 38400 tty6 # Example how to put a getty on a serial line (for a terminal) # #T0:23:respawn:/sbin/getty -L ttyS0 9600 vt100 #T1:23:respawn:/sbin/getty -L ttyS1 9600 vt100 # Example how to put a getty on a modem line. # #T3:23:respawn:/sbin/mgetty -x0 -s 57600 ttyS3 Undocumented features The letters A-C can be used to spawn a daemon listed in /etc/inittab. For example, assuming you want to start getty on a port to receive a call, but only after receiving a voice call first (and not all the time). Furthermore, you want to be able to receive a data or a fax call and that when you get the voice message you'll know which you want. You insert two new lines in /etc/inittab, each with its own ID, and each with a runlevel such as A for data and B for fax. When you know which you need, you simply spawn the appropriate daemon by calling 'telinit A' or 'telinit B'. The appropriate getty is put on the line until the first call is received. When the caller terminates the connection, the getty drops because, by definition, on demand will not respawn. The other two letters, S and Q, are special. S brings you system to maintenance mode and is the same as changing state to runlevel 1. The Q is used to tell init to reread inittab. The /etc/inittab file can be changed as often as required, but will only be read under certain circumstances: -One of its processes dies (do you need to respawn another?) -On a powerful signal from a power daemon (or a command line) -When told to change state by telinit The Q argument tells init to reread the /etc/inittab file. Even though it is called the System V runlevel system runlevels 7-9 are legitimate runlevels that can be used if necessary. The administrator must remember to alter the inittab file though and also to create the required rc?.d files. /etc/inputrc Global inputrc for libreadline. Readline is a function that gets a line from a user and automatically edits it. /etc/isapnp.conf Configuration file for ISA based cards. This standard is virtually redundant in new systems. The 'isapnptools' suite of ISA Plug-And-Play configuration utilities is used to configure such devices. These programs are suitable for all systems, whether or not they include a PnP BIOS. In fact, PnP BIOS adds some complications because it may already activate some cards so that the drivers can find them, and these tools can unconfigure them, or change their settings causing all sorts of nasty effects. /etc/isdn ISDN configuration files. /etc/issue Output by getty before the login prompt. Usually contains a short description or welcoming message to the system. The contents are up to the system administrator. Debian GNU/\s 3.0 \n \l /etc/issue.net Presents the welcome screen to users who login remotely to your machine (whereas /etc/issue determines what a local user sees on login). Debian GNU/%s 3.0 %h /etc/kde KDE initialization scripts and KDM configuration. /etc/kde/kdm Location for the K Desktop Manager files. kdm manages a collection of X servers, which may be on the local host or remote machines. It provides services similar to those provided by init, getty, and login on character-based terminals: prompting for login name and password, authenticating the user, and running a session. kdm supports XDMCP (X Display Manager Control Protocol) and can also be used to run a chooser process which presents the user with a menu of possible hosts that offer XDMCP display management. /etc/kderc System wide KDE initialization script. Commands here executed every time the KDE environment is loaded. It's a link to /etc/kde2/system.kdeglobals [Directories] dir_config=/etc/kde2 dir_html=/usr/share/doc/kde/HTML dir_cgi=/usr/lib/cgi-bin dir_apps=/usr/share/applnk dir_mime=/usr/share/mimelnk dir_services=/usr/share/services dir_servicetypes=/usr/share/servicetypes [General] TerminalApplication=x-terminal-emulator /etc/ld.so.conf, /etc/ld.so.cache /etc/ld.so.conf is a file containing a list of colon, space, tab, newline, or comma separated directories in which to search for libraries. /etc/ld.so.cache containing an ordered list of libraries found in the directories specified in /etc/ld.so.conf. This file is not in human readable format, and is not intended to be edited. 'ldconfig' creates the necessary links and cache (for use by the run-time linker, ld.so) to the most recent shared libraries found in the directories specified on the command line, in the file /etc/ ld.so.conf, and in the trusted directories (/usr/lib and /lib). 'ldconfig' checks the header and file names of the libraries it encounters when determining which versions should have their links updated. ldconfig ignores symbolic links when scanning for libraries. 'ldconfig' will attempt to deduce the type of ELF libs (ie. libc5 or libc6/glibc) based on what C libs if any the library was linked against, therefore when making dynamic libraries, it is wise to explicitly link against libc (use -lc). Some existing libs do not contain enough information to allow the deduction of their type, therefore the /etc/ld.so.conf file format allows the specification of an expected type. This is only used for those ELF libs which we can not work out. The format is like this "dirname=TYPE", where type can be libc4, libc5 or libc6. (This syntax also works on the command line). Spaces are not allowed. Also see the -p option. Directory names containing an = are no longer legal unless they also have an expected type specifier. 'ldconfig' should normally be run by the super-user as it may require write permission on some root owned directories and files. It is normally run automatically at bootup or manually whenever new shared libraries are installed. /usr/X11R6/lib X libraries. /usr/local/lib Local libraries. /etc/lilo.conf Configuration file for the Linux boot loader 'lilo'. 'lilo' is the original OS loader and can load Linux and others. The 'lilo' package normally contains lilo (the installer) and boot-record-images to install Linux, OS/2, DOS and generic Boot Sectors of other Oses. You can use Lilo to manage your Master Boot Record (with a simple text screen, text menu or colorful splash graphics) or call 'lilo' from other boot-loaders to jump-start the Linux kernel. Prompt #Prompt user to select OS choice at boot timeout=300 # Amount of time to wait before default OS # started (in ms) default=Debian4 #Default OS to be loaded vga=normal #VGA mode boot=/dev/had #location of MBR map=/boot/map #location of kernel install=/boot/boot-bmp.b #File to be installed as boot sector bitmap=/boot/debian.bmp #LILO boot image bmp-table=30p,100p,1,10 #Colours selectable bmp-colors=13,,0,1,,0 #Colours chosen lba32 #Required on most new systems to overcome #1024 cylinder problem image=/vmlinuz #name of kernel image label=Debian #a label read-only #file system to be mounted read only root=/dev/hda6 #location of root filesystem image=/boot/bzImage label=Debian4 read-only root=/dev/hda6 image=/mnt/redhat/boot/vmlinuz label=Redhat initrd=/mnt/redhat/boot/initrd-2.4.18-14.img read-only root=/dev/hda5 vga=788 append=" hdc=ide-scsi hdd=ide-scsi" image=/mnt/mandrake/boot/vmlinuz label="Mandrake" root=/dev/hda7 initrd=/mnt/mandrake/boot/initrd.img append="devfs=mount hdc=ide-scsi acpi=off quiet" vga=788 read-only other=/dev/hda2 table=/dev/hda loader=/boot/chain.b label=FBSD other=/dev/hda1 label=Windows table=/dev/hda other=/dev/fd0 label=floppy unsafe /etc/local.gen This file lists locales that you wish to have built. You can find a list of valid supported locales at /usr/share/i18n/SUPPORTED. Other combinations are possible, but may not be well tested. If you change this file, you need to re-run locale-gen. /etc/locale.alias Locale name alias data base. /etc/login.defs Configuration control definitions for the login package. An inordinate number of attributes can be altered via this single file such as the location of mail, delay in seconds after a failed login, enabling display of fail log information, display of unknown username login failures, shell environment variables, etc.... /etc/logrotate.conf The logrotate utility is designed to simplify the administration of log files on a system which generates a lot of log files. Logrotate allows for the automatic rotation compression, removal and mailing of log files. Logrotate can be set to handle a log file daily, weekly, monthly or when the log file gets to a certain size. Normally, logrotate runs as a daily cron job. # see "man logrotate" for details # rotate log files weekly weekly # keep 4 weeks worth of backlogs rotate 4 # create new (empty) log files after rotating old ones create # uncomment this if you want your log files compressed #compress # packages drop log rotation information into this directory include /etc/logrotate.d # no packages own wtmp, or btmp -- we'll rotate them here /var/log/wtmp { monthly create 0664 root utmp rotate 1 } /var/log/btmp { missingok monthly create 0664 root utmp rotate 1 } # system-specific logs may be configured here /etc/ltrace.conf Configuration file for ltrace (Library Call Tracer). It tracks runtime library calls in dynamically linked programs. 'ltrace' is a debugging program which runs a specified command until it exits. While the command is executing, ltrace intercepts and records the dynamic library calls which are called by the executed process and the signals received by that process. It can also intercept and print the system calls executed by the program. The program to be traced need not be recompiled for this, so you can use it on binaries for which you don't have the source handy. You should install ltrace if you need a sysadmin tool for tracking the execution of processes. /etc/magic Magic local data and configuration file for the file(1) command. Contains the descriptions of various file formats based on which file guesses the type of the file. Insert here your local magic data. Format is described in magic(5). /etc/mail.rc Initialization file for 'mail'. 'mail' is an intelligent mail processing system which has a command syntax reminiscent of ed with lines replaced by messages. It's basically a command line version of Microsoft Outlook. /etc/mailcap 'metamail' capabilities file. The mailcap file is read by the metamail program to determine how to display non-text at the local site. The syntax of a mailcap file is quite simple, at least compared to termcap files. Any line that starts with "#" is a comment. Blank lines are ignored. Otherwise, each line defines a single mailcap entry for a single content type. Long lines may be continued by ending them with a backslash character, \. Each individual mailcap entry consists of a content-type specification, a command to execute, and (possibly) a set of optional "flag" values. /etc/mailcap.order The mailcap ordering specifications. The order of entries in the /etc/ mailcap file can be altered by editing the /etc/mailcap.order file. Each line of that file specifies a package and an optional mime type. Mailcap entries that match will be placed in the order of this file. Entries that don't match will be placed later. /etc/mailname Mail server hostname. Normally the same as the hostname. /etc/menu, /etc/menu-methods The menu package was inspired by the install-fvwm2-menu program from the old fvwm2 package. However, menu tries to provide a more general interface for menu building. With the update-menus command from this package, no package needs to be modified for every X window manager again, and it provides a unified interface for both text-and X-oriented programs. When a package that wants to add something to the menu tree gets installed, it will run update-menus in its postinstall script. Update-menus then reads in all menu files in /etc/menu/ /usr/lib/menu and /usr/lib/menu/default, and stores the menu entries of all installed packages in memory. Once that has been done, it will run the menu-methods in /etc/menu-methods/*, and pipe the information about the menu entries to the menu-methods on stdout, so that the menu-methods can read this. Each Window Manager or other program that wants to have the debian menu tree, will supply a menu-method script in /etc/menu-methods/. This menu-method then knows how to generate the startup-file for that window manager. To facilitate this task for the window-manager maintainers, menu provides a install-menu program. This program can generate the startup files for just about every window manager. /etc/mgetty+sendfax Configuration files for use of mgetty as the interface on the serial port. The mgetty routine special routine has special features for handling things such as dial up connections and fax connections. /etc/mime.types MIME-TYPES and the extensions that represent them. This file is part of the "mime-support" package. Note: Compression schemes like "gzip", "bzip", and "compress" are not actually "mime-types". They are "encodings" and hence must _not_ have entries in this file to map their extensions. The "mime-type" of an encoded file refers to the type of data that has been encoded, not the type of the encoding. /etc/minicom 'minicom' configuration files. 'minicom' is a communication program which somewhat resembles the shareware program TELIX but is free with source code and runs under most unices. Features include dialling directory with auto-redial, support for UUCP-style lock files on serial devices, a separate script language interpreter, capture to file, multiple users with individual configurations, and more. /etc/modules List of modules to be loaded at startup. # /etc/modules: kernel modules to load at boot time. # # This file should contain the names of kernel modules that are # to be loaded at boot time, one per line. Comments begin with # a "#", and everything on the line after them are ignored. unix af_packet via-rhine cmpci ne2k-pci nvidia /etc/modules.conf ### This file is automatically generated by update-modules" # # Please do not edit this file directly. If you want to change or add # anything please take a look at the files in /etc/modutils and read # the manpage for update-modules. # ### update-modules: start processing /etc/modutils/0keep # DO NOT MODIFY THIS FILE! # This file is not marked as conffile to make sure if you upgrade modutils # it will be restored in case some modifications have been made. # # The keep command is necessary to prevent insmod and friends from ignoring # the builtin defaults of a path-statement is encountered. Until all other # packages use the new `add path'-statement this keep-statement is essential # to keep your system working keep ### update-modules: end processing /etc/modutils/0keep ### update-modules: start processing /etc/modutils/actions # Special actions that are needed for some modules # The BTTV module does not load the tuner module automatically, # so do that in here post-install bttv insmod tuner post-remove bttv rmmod tuner ### update-modules: end processing /etc/modutils/actions ### update-modules: start processing /etc/modutils/aliases # Aliases to tell insmod/modprobe which modules to use # Uncomment the network protocols you don't want loaded: # alias net-pf-1 off # Unix # alias net-pf-2 off # IPv4 # alias net-pf-3 off # Amateur Radio AX.25 # alias net-pf-4 off # IPX # alias net-pf-5 off # DDP / appletalk # alias net-pf-6 off # Amateur Radio NET/ROM # alias net-pf-9 off # X.25 # alias net-pf-10 off # IPv6 # alias net-pf-11 off # ROSE / Amateur Radio X.25 PLP # alias net-pf-19 off # Acorn Econet alias char-major-10-175 agpgart alias char-major-10-200 tun alias char-major-81 bttv alias char-major-108 ppp_generic alias /dev/ppp ppp_generic alias tty-ldisc-3 ppp_async alias tty-ldisc-14 ppp_synctty alias ppp-compress-21 bsd_comp alias ppp-compress-24 ppp_deflate alias ppp-compress-26 ppp_deflate # Crypto modules (see http://www.kerneli.org/) alias loop-xfer-gen-0 loop_gen alias loop-xfer-3 loop_fish2 alias loop-xfer-gen-10 loop_gen alias cipher-2 des alias cipher-3 fish2 alias cipher-4 blowfish alias cipher-6 idea alias cipher-7 serp6f alias cipher-8 mars6 alias cipher-11 rc62 alias cipher-15 dfc2 alias cipher-16 rijndael alias cipher-17 rc5 ### update-modules: end processing /etc/modutils/aliases ### update-modules: start processing /etc/modutils/ltmodem-2.4.18 # lt_drivers: autoloading and insertion parameter usage alias char-major-62 lt_serial alias /dev/tts/LT0 lt_serial alias /dev/modem lt_serial # options lt_modem vendor_id=0x115d device_id=0x0420 Forced=3,0x130,0x2f8 # section for lt_drivers ends ### update-modules: end processing /etc/modutils/ltmodem-2.4.18 ### update-modules: start processing /etc/modutils/paths # This file contains a list of paths that modprobe should scan, # beside the once that are compiled into the modutils tools # themselves. ### update-modules: end processing /etc/modutils/paths ### update-modules: start processing /etc/modutils/ppp alias /dev/ppp ppp_generic alias char-major-108 ppp_generic alias tty-ldisc-3 ppp_async alias tty-ldisc-14 ppp_synctty alias ppp-compress-21 bsd_comp alias ppp-compress-24 ppp_deflate alias ppp-compress-26 ppp_deflate ### update-modules: end processing /etc/modutils/ppp ### update-modules: start processing /etc/modutils/setserial # # This is what I wanted to do, but logger is in /usr/bin, which isn't # loaded when the module is first loaded into the kernel at boot time! # #post-install serial /etc/init.d/setserial start | #logger -p daemon.info -t "setserial-module reload" #pre-remove serial /etc/init.d/setserial stop | #logger -p daemon.info -t "setserial-module uload" # alias /dev/tts serial alias /dev/tts/0 serial alias /dev/tts/1 serial alias /dev/tts/2 serial alias /dev/tts/3 serial post-install serial /etc/init.d/setserial modload > /dev/null 2> /dev/null pre-remove serial /etc/init.d/setserial modsave > /dev/null 2> /dev/null ### update-modules: end processing /etc/modutils/setserial ### update-modules: start processing /etc/modutils/arch/i386 alias parport_lowlevel parport_pc alias char-major-10-144 nvram alias binfmt-0064 binfmt_aout alias char-major-10-135 rtc ### update-modules: end processing /etc/modutils/arch/i386 /etc/modutils These utilities are intended to make a Linux modular kernel manageable for all users, administrators and distribution maintainers. /etc/mtools Debian default mtools configuration file. The mtools series of commands work with MS-DOS files and directories on floppy disks. This allows you to use Linux with MS-DOS formatted diskettes on DOS and Windows systems. /etc/manpath.conf This file is used by the man_db package to configure the man and cat paths. It is also used to provide a manpath for those without one by examining their PATH environment variable. For details see the manpath(5) man page. /etc/mediaprm Was formally named /etc/fdprm. See /etc/fdprm for further details. /etc/motd The message of the day, automatically output after a successful login. Contents are up to the system administrator. Often used for getting information to every user, such as warnings about planned downtimes. Linux debian.localdomain.com 2.4.18 #1 Sat Mar 15 00:17:39 EST 2003 i686 unknown Most of the programs included with the Debian GNU/Linux system are freely redistributable; the exact distribution terms for each program are described in the individual files in /usr/share/doc/*/copyright Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent permitted by applicable law. /etc/mtab List of currently mounted filesystems. Initially set up by the bootup scripts, and updated automatically by the mount command. Used when a list of mounted filesystems is needed, e.g., by the df command. This file is sometimes a symbolic link to /proc/mounts. /etc/networks List of networks that the system is currently located on. For example, 192.168.0.0. /etc/nsswitch.conf System Database/Name Service Switch configuration file. /etc/oss.conf OSS (Open Sound System) configuration file. /etc/pam.d/ This directory is the home of the configuration files for PAMs, Pluggable Authentication Modules. /etc/postfix/ Holds your postfix configuration files. Postfix is now the MTA of choice among Linux distributions. It is sendmail-compatible, offers improved speed over sendmail, ease of administration and security. It was originally developed by IBM and was called the IBM Secure Mailer and is used in many large commercial networks. It is now the de-facto standard. /etc/ppp/ The place where your dial-up configuration files are placed. More than likely to be created by the text menu based pppconfig or other GUI based ppp configuration utilities such as kppp or gnome-ppp. /etc/pam.conf Most programs use a file under the /etc/pam.d/ directory to setup their PAM service modules. This file is and can be used, but is not recommended. /etc/paper.config Paper size configuration file. /etc/papersize Default papersize. /etc/passwd This is the 'old' password file, It is kept for compatibility and contains the user database, with fields giving the username, real name, home directory, encrypted password, and other information about each user. The format is documented in the passwd man(ual) page. root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/bin/sh bin:x:2:2:bin:/bin:/bin/sh sys:x:3:3:sys:/dev:/bin/sh sync:x:4:100:sync:/bin:/bin/sync games:x:5:100:games:/usr/games:/bin/sh man:x:6:100:man:/var/cache/man:/bin/sh lp:x:7:7:lp:/var/spool/lpd:/bin/sh mail:x:8:8:mail:/var/mail:/bin/sh news:x:9:9:news:/var/spool/news:/bin/sh uucp:x:10:10:uucp:/var/spool/uucp:/bin/sh proxy:x:13:13:proxy:/bin:/bin/sh postgres:x:31:32:postgres:/var/lib/postgres:/bin/sh www-data:x:33:33:www-data:/var/www:/bin/sh backup:x:34:34:backup:/var/backups:/bin/sh operator:x:37:37:Operator:/var:/bin/sh list:x:38:38:SmartList:/var/list:/bin/sh irc:x:39:39:ircd:/var:/bin/sh gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/bin/sh nobody:x:65534:65534:nobody:/home:/bin/sh binh:x:1000:1000:,,,:/home/binh:/bin/bash identd:x:100:65534::/var/run/identd:/bin/false sshd:x:101:65534::/var/run/sshd:/bin/false gdm:x:102:101:Gnome Display Manager:/var/lib/gdm:/bin/false telnetd:x:103:103::/usr/lib/telnetd:/bin/false dummy:x:1001:1001:,,,:/home/dummy:/bin/bash /etc/passwd- Old /etc/passwd file. /etc/printcap Printer configuration (capabilities) file. The definition of all system printers, whether local or remote, is stored in this file. Its layout is similar to that of /etc/termcap but it uses a different syntax. /etc/profile Files and commands to be executed at login or startup time by the Bourne or C shells. These allow the system administrator to set global defaults for all users. /etc/profile.d Shells scripts to be executed upon login to the Bourne or C shells. These scripts are normally called from the /etc/profile file. /etc/protocols Protocols definitions file. It describes the various DARPA Internet protocols that are available from the TCP/IP subsystem. It should be consulted instead of using the numbers in the ARPA include files or resorting to guesstimation. This file should be left untouched since changes could result in incorrect IP packages. /etc/pcmcia Configuration files for PCMCIA devices. Generally only useful to laptop users. /etc/reportbug.conf Configuration file for reportbug. Reportbug is primarily designed to report bugs in the Debian distribution. By default it creates an e-mail to the Debian bug tracking system at mit@bugs.debian.org with information about the bug. Using the -bts option you can report bugs to other servers also using ddebbugs such as KDE.org. It is similar to bug but has far greater capabilities while still maintaining simplicity. /etc/rc.boot or /etc/rc?.d These directories contain all the files necessary to control system services and configure runlevels. A skeleton file is provided in /etc/ init.d/skeleton /etc/rcS.d The scripts in this directory are executed once when booting the system, even when booting directly into single user mode. The files are all symbolic links, the real files are located in /etc/init.d/. For a more general discussion of this technique, see /etc/init.d/README. /etc/resolv.conf Configuration of how DNS is to occur is defined in this file. It tells the name resolver libraries where they need to go to find information not found in the /etc/hosts file. This always has at least one nameserver line, but preferably three. The resolver uses each in turn. More than the first three can be included but anything beyond the first three will be ignored. Two lines that appear in the /etc/resolv.conf file are domain and search. Both of these are mutually exclusive options, and where both show up, the last one wins. Other entries beyond the three discussed here are listed in the man pages but aren't often used. /etc/rmt This is not a mistake. This shell script (/etc/rmt) has been provided for compatibility with other Unix-like systems, some of which have utilities that expect to find (and execute) rmt in the /etc directory on remote systems. /etc/rpc The rpc file contains user readable names that can be used in place of rpc program numbers. Each line has the following information: -name of server for the rpc program -rpc program number -aliases Items are separated by any number of blanks and/or tab characters. A ``#'' indicates the beginning of a comment; characters up to the end of the line are not interpreted by routines which search the file. # /etc/rpc: # $Id: etc.xml,v 1.10 2004/02/03 21:42:57 binh Exp $ # # rpc 88/08/01 4.0 RPCSRC; from 1.12 88/02/07 SMI portmapper 100000 portmap sunrpc rstatd 100001 rstat rstat_svc rup perfmeter rusersd 100002 rusers nfs 100003 nfsprog ypserv 100004 ypprog mountd 100005 mount showmount ypbind 100007 walld 100008 rwall shutdown yppasswdd 100009 yppasswd etherstatd 100010 etherstat rquotad 100011 rquotaprog quota rquota sprayd 100012 spray 3270_mapper 100013 rje_mapper 100014 selection_svc 100015 selnsvc database_svc 100016 rexd 100017 rex alis 100018 sched 100019 llockmgr 100020 nlockmgr 100021 x25.inr 100022 statmon 100023 status 100024 bootparam 100026 ypupdated 100028 ypupdate keyserv 100029 keyserver tfsd 100037 nsed 100038 nsemntd 100039 pcnfsd 150001 amd 300019 amq sgi_fam 391002 ugidd 545580417 bwnfsd 788585389 /etc/samba Samba configuration files. A 'LanManager' like file and printer server for Unix. The Samba software suite is a collection of programs that implements the SMB protocol for unix systems, allowing you to serve files and printers to Windows, NT, OS/2 and DOS clients. This protocol is sometimes also referred to as the LanManager or NetBIOS protocol. /etc/sane.d Sane configuration files. SANE stands for "Scanner Access Now Easy" and is an application programming interface (API) that provides standardized access to any raster image scanner hardware (flatbed scanner, hand-held scanner, video- and still-cameras, frame-grabbers, etc.). The SANE API is public domain and its discussion and development is open to everybody. The current source code is written for UNIX (including GNU/Linux) and is available under the GNU General Public License (the SANE API is available to proprietary applications and backends as well, however). SANE is a universal scanner interface. The value of such a universal interface is that it allows writing just one driver per image acquisition device rather than one driver for each device and application. So, if you have three applications and four devices, traditionally you'd have had to write 12 different programs. With SANE, this number is reduced to seven: the three applications plus the four drivers. Of course, the savings get even bigger as more and more drivers and/or applications are added. Not only does SANE reduce development time and code duplication, it also raises the level at which applications can work. As such, it will enable applications that were previously unheard of in the UNIX world. While SANE is primarily targeted at a UNIX environment, the standard has been carefully designed to make it possible to implement the API on virtually any hardware or operating system. While SANE is an acronym for ``Scanner Access Now Easy'' the hope is of course that SANE is indeed sane in the sense that it will allow easy implementation of the API while accommodating all features required by today's scanner hardware and applications. Specifically, SANE should be broad enough to accommodate devices such as scanners, digital still and video cameras, as well as virtual devices like image file filters. If you're familiar with TWAIN, you may wonder why there is a need for SANE. Simply put, TWAIN does not separate the user-interface from the driver of a device. This, unfortunately, makes it difficult, if not impossible, to provide network transparent access to image acquisition devices (which is useful if you have a LAN full of machines, but scanners connected to only one or two machines; it's obviously also useful for remote-controlled cameras and such). It also means that any particular TWAIN driver is pretty much married to a particular GUI API (be it Win32 or the Mac API). In contrast, SANE cleanly separates device controls from their representation in a user-interface. As a result, SANE has no difficulty supporting command-line driven interfaces or network-transparent scanning. For these reasons, it is unlikely that there will ever be a SANE backend that can talk to a TWAIN driver. The converse is no problem though: it would be pretty straight forward to access SANE devices through a TWAIN source. In summary, if TWAIN had been just a little better designed, there would have been no reason for SANE to exist, but things being the way they are, TWAIN simply isn't SANE. /etc/securetty Identifies secure terminals, i.e., the terminals from which root is allowed to log in. Typically only the virtual consoles are listed, so that it becomes impossible (or at least harder) to gain superuser privileges by breaking into a system over a modem or a network. # /etc/securetty: list of terminals on which root is allowed to login. # See securetty(5) and login(1). console # Standard consoles tty1 tty2 tty3 tty4 tty5 tty6 tty7 tty8 tty9 tty10 tty11 tty12 # Same as above, but these only occur with devfs devices vc/1 vc/2 vc/3 vc/4 vc/5 vc/6 vc/7 vc/8 vc/9 vc/10 vc/11 vc/12 /etc/sensors.conf Configuration file for libsensors. A set of libraries designed to ascertain current hardware states via motherboard sensor chips. Useful statistics such as core voltages, CPU temperature can be determined through third party utilities that make user of these libraries such as 'gkrellm'. If you do not wish to install these packages you may also utilise the /proc filesystem real-time nature. /etc/sudoers Sudoers file. This file must be edited with the 'visudo' command as root. The sudo command allows an authenticated user to execute an authorized command as root. Both the effective UID and GID are set to 0 (you are basically root). It determines which users are authorized and which commands they are authorized to use. Configuration of this command is via this file. /etc/shadow Shadow password file on systems with shadow password software installed (PAMs). Shadow passwords move the encrypted password from /etc/passwd into /etc/shadow; the latter is not readable by anyone except root. This makes it more difficult to crack passwords. /etc/shadow- Old /etc/shadow file. /etc/sysctl.conf Configuration file for setting system variables, most notably kernel parameters. 'sysctl' is a means of configuring certain aspects of the kernel at run-time, and the /proc/sys/ directory is there so that you don't even need special tools to do it! /etc/security Essential to security. This subdirectory allows administrators to impose quota limits, access limits and also to configure PAM environments. /etc/serial.conf Serial port configuration. Changeable parameters include speed, baud rate, port, irq and type. /etc/services A definition of the networks, services and the associated port for each protocol that are available on this system. For example, web services (http) are assigned to port 80 by default. # /etc/services: # $Id: etc.xml,v 1.10 2004/02/03 21:42:57 binh Exp $ # # Network services, Internet style # # Note that it is presently the policy of IANA to assign a single # well-known port number for both TCP and UDP; hence, most entries # here have two entries even if the protocol doesn't support UDP # operations. Updated from RFC 1700, ``Assigned Numbers'' (October # 1994). Not all ports are included, only the more common ones. echo 7/tcp echo 7/udp discard 9/tcp sink null discard 9/udp sink null systat 11/tcp users daytime 13/tcp daytime 13/udp netstat 15/tcp qotd 17/tcp quote msp 18/tcp # message send protocol msp 18/udp # message send protocol chargen 19/tcp ttytst source chargen 19/udp ttytst source ftp-data 20/tcp ftp 21/ tcp fsp 21/udp fspd ssh 22/tcp # SSH Remote Login Protocol ssh 22/udp # SSH Remote Login Protocol telnet 23/tcp # 24 - private smtp 25/tcp mail # 26 - unassigned time 37/tcp timserver time 37/udp timserver rlp 39/udp resource # resource location nameserver 42/tcp name # IEN 116 whois 43/ tcp nicname re-mail-ck 50/tcp # Remote Mail Checking Protocol re-mail-ck 50/udp # Remote Mail Checking Protocol domain 53/tcp nameserver # name-domain server domain 53/udp nameserver netbios-ns 137/tcp # NETBIOS Name Service netbios-ns 137/udp netbios-dgm 138/tcp # NETBIOS Datagram Service netbios-dgm 138/udp netbios-ssn 139/tcp # NETBIOS session service netbios-ssn 139/udp x11 6000/tcp x11-0 # X windows system x11 6000/udp x11-0 # X windows system /etc/shells Lists trusted shells. The chsh command allows users to change their login shell only to shells listed in this file. ftpd, the server process that provides FTP services for a machine, will check that the user's shell is listed in /etc/shells and will not let people log in unless the shell is listed there. There are also some display managers that will passively or actively (dependent upon on distribution and display manager being used) refuse a user access to the system unless their shell is one of those listed here. # /etc/shells: valid login shells /bin/ash /bin/bash /bin/csh /bin/sh /usr/bin/es /usr/bin/ksh /bin/ksh /usr/bin/rc /usr/bin/tcsh /bin/tcsh /usr/bin/zsh /bin/sash /bin/zsh /usr/bin/esh /etc/skel/ The default files for each new user are stored in this directory. Each time a new user is added, these skeleton files are copied into their home directory. An average system would have: .alias, .bash_profile, .bashrc and .cshrc files. Other files are left up to the system administrator. /etc/sysconfig/ This directory contains configuration files and subdirectories for the setup of system configuration specifics and for the boot process, like 'clock', which sets the timezone, or 'keyboard' which controls the keyboard map. The contents may vary drastically depending on which distribution and what utilities you have installed. For example, on a Redhat or Mandrake based system it is possible to alter an endless array of attributes from the default desktop to whether DMA should be enabled for your IDE devices. On our Debian reference system though this folder is almost expedient containing only two files hwconf and soundcard which are both configured by the Redhat utilities hwconf and sndconfig respectively. /etc/slip Configuration files for the setup and operation of SLIP (serial line IP) interface. Generally unused nowadays. This protocol has been superceded by the faster and more efficient PPP protocol. /etc/screenrc This is the system wide screenrc. You can use this file to change the default behavior of screen system wide or copy it to ~/.screenrc and use it as a starting point for your own settings. Commands in this file are used to set options, bind screen functions to keys, redefine terminal capabilities, and to automatically establish one or more windows at the beginning of your screen session. This is not a comprehensive list of options, look at the screen manual for details on everything that you can put in this file. /etc/scrollkeeper.conf A free electronic cataloging system for documentation. It stores metadata specified by the http://www.ibiblio.org/osrt/omf/ (Open Source Metadata Framework) as well as certain metadata extracted directly from documents (such as the table of contents). It provides various functionality pertaining to this metadata to help browsers, such as sorting the registered documents or searching the metadata for documents which satisfy a set of criteria. /etc/ssh 'ssh' configuration files. 'ssh' is a secure rlogin/rsh/rcp replacement (OpenSSH). This is the portable version of OpenSSH, a free implementation of the Secure Shell protocol as specified by the IETF secsh working group. 'ssh' (Secure Shell) is a program for logging into a remote machine and for executing commands on a remote machine. It provides secure encrypted communications between two untrusted hosts over an insecure network. X11 connections and arbitrary TCP/IP ports can also be forwarded over the secure channel. It is intended as a replacement for rlogin, rsh and rcp, and can be used to provide applications with a secure communication channel. It should be noted that in some countries, particularly Iraq, and Pakistan, it may be illegal to use any encryption at all without a special permit. /etc/syslog.conf Lists where log files should go, what messages are written to them and the level of verbosity. It is also now possible to filter based on message content, message integrity, message encryption (near future), portability and better network forwarding. /etc/termcap The terminal capability database. Describes the "escape sequences" by which various terminals can be controlled. Programs are written so that instead of directly outputting an escape sequence that only works on a particular brand of terminal, they look up the correct sequence to do whatever it is they want to do in /etc/termcap. As a result most programs work with most kinds of terminals. /etc/timezone local timezone. /etc/updatedb.conf Sets environment variables that are used by updatedb which therefore configures the database for 'locate', a utility that locates a pattern in a database of filenames and returns the filenames that match. # This file sets environment variables which are used by updatedb # filesystems which are pruned from updatedb database PRUNEFS="NFS nfs afs proc smbfs autofs auto iso9660 ncpfs coda devpts ftpfs" export PRUNEFS # paths which are pruned from updatedb database PRUNEPATHS="/tmp /usr/tmp /var/tmp /afs /amd /alex /var/spool" export PRUNEPATHS # netpaths which are added NETPATHS="" export NETPATHS /etc/vga The configuration file for the svgalib is stored in this directory. svgalib provides graphics capabilities to programs running on the system console, without going through the X Window System. It uses direct access to the video hardware to provide low-level access to the standard VGA and SVGA graphics modes. It only works with some video hardware; so use with caution. /etc/vim Contains configuration files for both vim and its X based counterpart gvim. A wide range of options can be accessed though these two files such as automatic indentation, syntax highlighting, etc.... /etc/xinetd.d/ The original 'inetd' daemon has now been superceded by the much improved 'xinetd'. 'inetd' should be run at boot time by /etc/init.d/inetd (or / etc/rc.local on some systems). It then listens for connections on certain Internet sockets. When a connection is found on one of its sockets, it decides what service the socket corresponds to, and invokes a program to service the request. After the program is finished, it continues to listen on the socket (except in some cases). Essentially, inetd allows running one daemon to invoke several others, reducing load on the system. Services controlled via xinetd put their configuration files here. /etc/zlogin System-wide .zlogin file for zsh(1). This file is sourced only for login shells. It should contain commands that should be executed only in login shells. It should be used to set the terminal type and run a series of external commands (fortune, msgs, from, etc.) /etc/zlogout Commands to be executed upon user exit from the zsh. Its control is system-wide but the .zlogout file for zsh(1) does override it in terms of importance. /etc/zprofile System-wide .zprofile file for zsh(1). This file is sourced only for login shells (i.e. Shells invoked with "-" as the first character of argv [0], and shells invoked with the -l flag.) /etc/zshenv System-wide .zshenv file for zsh(1). This file is sourced on all invocations of the shell. If the -f flag is present or if the NO_RCS option is set within this file, all other initialization files are skipped. This file should contain commands to set the command search path, plus other important environment variables. This file should not contain commands that produce output or assume the shell is attached to a tty. /etc/zshrc System-wide .zshrc file for zsh(1). This file is sourced only for interactive shells. It should contain commands to set up aliases, functions, options, key bindings, etc. Compliance with the FSSTND requires that the following directories, or symbolic links to directories are required in /etc: opt Configuration for /opt X11 Configuration for the X Window system (optional) sgml Configuration for SGML (optional) xml Configuration for XML (optional) The following directories, or symbolic links to directories must be in /etc, if the corresponding subsystem is installed: opt Configuration for /opt The following files, or symbolic links to files, must be in /etc if the corresponding subsystem is installed (it is recommended that files be stored in subdirectories of /etc/ rather than directly in /etc: csh.login Systemwide initialization file for C shell logins (optional) exports NFS filesystem access control list (optional) fstab Static information about filesystems (optional) ftpusers FTP daemon user access control list (optional) gateways File which lists gateways for routed (optional) gettydefs Speed and terminal settings used by getty (optional) group User group file (optional) host.conf Resolver configuration file (optional) hosts Static information about host names (optional) hosts.allow Host access file for TCP wrappers (optional) hosts.deny Host access file for TCP wrappers (optional) hosts.equiv List of trusted hosts for rlogin, rsh, rcp (optional) hosts.lpd List of trusted hosts for lpd (optional) inetd.conf Configuration file for inetd (optional) inittab Configuration file for init (optional) issue Pre-login message and identification file (optional) ld.so.conf List of extra directories to search for shared libraries (optional) motd Post-login message of the day file (optional) mtab Dynamic information about filesystems (optional) mtools.conf Configuration file for mtools (optional) networks Static information about network names (optional) passwd The password file (optional) printcap The lpd printer capability database (optional) profile Systemwide initialization file for sh shell logins (optional) protocols IP protocol listing (optional) resolv.conf Resolver configuration file (optional) rpc RPC protocol listing (optional) securetty TTY access control for root login (optional) services Port names for network services (optional) shells Pathnames of valid login shells (optional) syslog.conf Configuration file for syslogd (optional) mtab does not fit the static nature of /etc: it is excepted for historical reasons. On some Linux systems, this may be a symbolic link to /proc/mounts, in which case this exception is not required. /etc/opt : Configuration files for /opt Host-specific configuration files for add-on application software packages must be installed within the directory /etc/opt/&60;subdir&62;, where &60;subdir&62; is the name of the subtree in /opt where the static data from that package is stored. No structure is imposed on the internal arrangement of /etc/opt/&60;subdir&62;. If a configuration file must reside in a different location in order for the package or system to function properly, it may be placed in a location other than /etc/opt/&60;subdir&62;. The rationale behind this subtree is best explained by refering to the rationale for /opt. /etc/X11 : Configuration for the X Window System (optional) /etc/X11 is the location for all X11 host-specific configuration. This directory is necessary to allow local control if /usr is mounted read only. The following files, or symbolic links to files, must be in /etc/X11 if the corresponding subsystem is installed: Xconfig The configuration file for early versions of XFree86 (optional) XF86Config The configuration file for XFree86 versions 3 and 4 (optional) Xmodmap Global X11 keyboard modification file (optional) Subdirectories of /etc/X11 may include those for xdm and for any other programs (some window managers, for example) that need them. /etc/X11/xdm holds the configuration files for xdm. These are most of the files previously found in /usr/lib/X11/xdm. Some local variable data for xdm is stored in /var/lib/xdm. It is recommended that window managers with only one configuration file which is a default .*wmrc file must name it system.*wmrc (unless there is a widely-accepted alternative name) and not use a subdirectory. Any window manager subdirectories must be identically named to the actual window manager binary. /etc/sgml : Configuration files for SGML (optional) Generic configuration files defining high-level parameters of the SGML systems are installed here. Files with names *.conf indicate generic configuration files. File with names *.cat are the DTD-specific centralized catalogs, containing references to all other catalogs needed to use the given DTD. The super catalog file catalog references all the centralized catalogs. /etc/xml : Configuration files for XML (optional) Generic configuration files defining high-level parameters of the XML systems are installed here. Files with names *.conf indicate generic configuration files. The super catalog file catalog references all the centralized catalogs. ----------------------------------------------------------------------------- 1.7. /home Linux is a multi-user environment so each user is also assigned a specific directory that is accessible only to them and the system administrator. These are the user home directories, which can be found under '/home/$USER' (~/). It is your playground: everything is at your command, you can write files, delete them, install programs, etc.... Your home directory contains your personal configuration files, the so-called dot files (their name is preceded by a dot). Personal configuration files are usually 'hidden', if you want to see them, you either have to turn on the appropriate option in your file manager or run ls with the -a switch. If there is a conflict between personal and system wide configuration files, the settings in the personal file will prevail. Dotfiles most likely to be altered by the end user are probably your .xsession and .bashrc files. The configuration files for X and Bash respectively. They allow you to be able to change the window manager to be startup upon login and also aliases, user-specified commands and environment variables respectively. Almost always when a user is created their dotfiles will be taken from the /etc/skel directory where system administrators place a sample file that user's can modify to their hearts content. /home can get quite large and can be used for storing downloads, compiling, installing and running programs, your mail, your collection of image or sound files etc. The FSSTND states that: /home is a fairly standard concept, but it is clearly a site-specific filesystem. Different people prefer to place user accounts in a variety of places. This section describes only a suggested placement for user home directories; nevertheless we recommend that all FHS-compliant distributions use this as the default location for home directories. On small systems, each user's directory is typically one of the many subdirectories of /home such as /home/smith, /home/torvalds, /home/operator, etc. On large systems (especially when the /home directories are shared amongst many hosts using NFS) it is useful to subdivide user home directories. Subdivision may be accomplished by using subdirectories such as /home/staff, /home/guests, /home/students, etc. The setup will differ from host to host. Therefore, no program should rely on this location. If you want to find out a user's home directory, you should use the getpwent(3) library function rather than relying on /etc/passwd because user information may be stored remotely using systems such as NIS. User specific configuration files for applications are stored in the user's home directory in a file that starts with the '.' character (a "dot file"). If an application needs to create more than one dot file then they should be placed in a subdirectory with a name starting with a '.' character, (a "dot directory"). In this case the configuration files should not start with the '.' character. It is recommended that apart from autosave and lock files programs should refrain from creating non dot files or directories in a home directory without user intervention. ----------------------------------------------------------------------------- 1.8. /initrd initrd provides the capability to load a RAM disk by the boot loader. This RAM disk can then be mounted as the root file system and programs can be run from it. Afterwards, a new root file system can be mounted from a different device. The previous root (from initrd) is then moved to a directory and can be subsequently unmounted. initrd is mainly designed to allow system startup to occur in two phases, where the kernel comes up with a minimum set of compiled-in drivers, and where additional modules are loaded from initrd. Operation --------- When using initrd, the system typically boots as follows: 1) the boot loader loads the kernel and the initial RAM disk 2) the kernel converts initrd into a "normal" RAM disk and frees the memory used by initrd 3) initrd is mounted read-write as root 4) /linuxrc is executed (this can be any valid executable, including shell scripts; it is run with uid 0 and can do basically everything init can do) 5) linuxrc mounts the "real" root file system 6) linuxrc places the root file system at the root directory using the pivot_root system call 7) the usual boot sequence (e.g. invocation of /sbin/init) is performed on the root file system 8) the initrd file system is removed Note that changing the root directory does not involve unmounting it. It is therefore possible to leave processes running on initrd during that procedure. Also note that file systems mounted under initrd continue to be accessible. Usage scenarios --------------- The main motivation for implementing initrd was to allow for modular kernel configuration at system installation. The procedure would work as follows: 1) system boots from floppy or other media with a minimal kernel (e.g. support for RAM disks, initrd, a.out, and the Ext2 FS) and loads initrd 2) /linuxrc determines what is needed to (1) mount the "real" root FS (i.e. device type, device drivers, file system) and (2) the distribution media (e.g. CD-ROM, network, tape, ...). This can be done by asking the user, by auto-probing, or by using a hybrid approach. 3) /linuxrc loads the necessary kernel modules 4) /linuxrc creates and populates the root file system (this doesn't have to be a very usable system yet) 5) /linuxrc invokes pivot_root to change the root file system and execs - via chroot - a program that continues the installation 6) the boot loader is installed 7) the boot loader is configured to load an initrd with the set of modules that was used to bring up the system (e.g. /initrd can be modified, then unmounted, and finally, the image is written from /dev/ram0 or /dev/rd/0 to a file) 8) now the system is bootable and additional installation tasks can be performed The key role of initrd here is to re-use the configuration data during normal system operation without requiring the use of a bloated "generic" kernel or re-compiling or re-linking the kernel. A second scenario is for installations where Linux runs on systems with different hardware configurations in a single administrative domain. In such cases, it is desirable to generate only a small set of kernels (ideally only one) and to keep the system-specific part of configuration information as small as possible. In this case, a common initrd could be generated with all the necessary modules. Then, only /linuxrc or a file read by it would have to be different. A third scenario are more convenient recovery disks, because information like the location of the root FS partition doesn't have to be provided at boot time, but the system loaded from initrd can invoke a user-friendly dialog and it can also perform some sanity checks (or even some form of auto-detection). Last not least, CD-ROM distributors may use it for better installation from CD, e.g. by using a boot floppy and bootstrapping a bigger RAM disk via initrd from CD; or by booting via a loader like LOADLIN or directly from the CD-ROM, and loading the RAM disk from CD without need of floppies. ----------------------------------------------------------------------------- 1.9. /lib The /lib directory contains kernel modules and those shared library images (the C programming code library) needed to boot the system and run the commands in the root filesystem, ie. by binaries in /bin and /sbin. Libraries are readily identifiable through their filename extension of *.so. Windows equivalent to a shared library would be a DLL (dynamically linked library) file. They are essential for basic system functionality. Kernel modules (drivers) are in the subdirectory /lib/modules/'kernel-version'. To ensure proper module compilation you should ensure that /lib/modules/ 'kernel-version'/kernel/build points to /usr/src/'kernel-version' or ensure that the Makefile knows where the kernel source itself are located. /lib/'machine-architecture' Contains platform/architecture dependent libraries. /lib/iptables iptables shared library files. /lib/kbd Contains various keymaps. /lib/modules/'kernel-version' The home of all the kernel modules. The organisation of files here is reasonably clear so no requires no elaboration. /lib/modules/'kernel-version'/isapnpmap.dep has details on ISA based cards, the modules that they require and various other attributes. /lib/modules/'kernel-version'/modules.dep lists all modules dependencies. This file can be updated using the depmod command. /lib/modules/'kernel-version'/pcimap is the PCI equivalent of the /lib/modules/'kernel-version'/isapnpmap.dep file. /lib/modules/'kernel-version'/usbmap is the USB equivalent of the /lib/modules/'kernel-version'/isapnpmap.dep file. /lib/oss All OSS (Open Sound System) files are installed here by default. /lib/security PAM library files. The FSSTND states that the /lib directory contains those shared library images needed to boot the system and run the commands in the root filesystem, ie. by binaries in /bin and /sbin. Shared libraries that are only necessary for binaries in /usr (such as any X Window binaries) must not be in /lib. Only the shared libraries required to run binaries in /bin and /sbin may be here. In particular, the library libm.so.* may also be placed in /usr/lib if it is not required by anything in /bin or /sbin. At least one of each of the following filename patterns are required (they may be files, or symbolic links): libc.so.* The dynamically-linked C library (optional) ld* The execution time linker/loader (optional) If a C preprocessor is installed, /lib/cpp must be a reference to it, for historical reasons. The usual placement of this binary is /usr/bin/cpp. The following directories, or symbolic links to directories, must be in /lib, if the corresponding subsystem is installed: modules Loadable kernel modules (optional) /lib : Alternate format essential shared libraries (optional) There may be one or more variants of the /lib directory on systems which support more than one binary format requiring separate libraries. This is commonly used for 64-bit or 32-bit support on systems which support multiple binary formats, but require libraries of the same name. In this case, /lib32 and /lib64 might be the library directories, and /lib a symlink to one of them. If one or more of these directories exist, the requirements for their contents are the same as the normal /lib directory, except that /lib/cpp is not required. /lib/cpp is still permitted: this allows the case where /lib and /lib are the same (one is a symbolic link to the other). ----------------------------------------------------------------------------- 1.10. /lost+found As was explained earlier during the overview of the FSSTND, Linux should always go through a proper shutdown. Sometimes your system might crash or a power failure might take the machine down. Either way, at the next boot, a lengthy filesystem check (the speed of this check is dependent on the type of filesystem that you actually use. ie. ext3 is faster than ext2 because it is a journalled filesystem) using fsck will be done. Fsck will go through the system and try to recover any corrupt files that it finds. The result of this recovery operation will be placed in this directory. The files recovered are not likely to be complete or make much sense but there always is a chance that something worthwhile is recovered. Each partition has its own lost+found directory. If you find files in there, try to move them back to their original location. If you find something like a broken symbolic link to 'file', you have to reinstall the file/s from the corresponding RPM, since your file system got damaged so badly that the files were mutilated beyond recognition. Below is an example of a /lost+found directory. As you can see, the vast majority of files contained here are in actual fact sockets. As for the rest of the other files they were found to be damaged system files and personal files. These files were not able to be recovered. total 368 -rw-r--r-- 1 root root 110891 Oct 5 14:14 #388200 -rw-r--r-- 1 root root 215 Oct 5 14:14 #388201 -rw-r--r-- 1 root root 110303 Oct 6 23:09 #388813 -rw-r--r-- 1 root root 141 Oct 6 23:09 #388814 -rw-r--r-- 1 root root 110604 Oct 6 23:09 #388815a -rw-r--r-- 1 root root 194 Oct 6 23:09 #388816 srwxr-xr-x 1 root root 0 Oct 6 13:00 #51430 srwxr-xr-x 1 root root 0 Oct 6 00:23 #51433 -rw------- 1 root root 63 Oct 6 00:23 #51434 srwxr-xr-x 1 root root 0 Oct 6 13:00 #51436 srwxrwxrwx 1 root root 0 Oct 6 00:23 #51437 srwx------ 1 root root 0 Oct 6 00:23 #51438 -rw------- 1 root root 63 Oct 6 13:00 #51439 srwxrwxrwx 1 root root 0 Oct 6 13:00 #51440 srwx------ 1 root root 0 Oct 6 13:00 #51442 -rw------- 1 root root 63 Oct 6 23:09 #51443 srwx------ 1 root root 0 Oct 6 10:40 #51445 srwxrwxrwx 1 root root 0 Oct 6 23:09 #51446 srwx------ 1 root root 0 Oct 6 23:09 #51448 ----------------------------------------------------------------------------- 1.11. /media Amid much controversy and consternation on the part of system and network administrators a directory containing mount points for removable media has now been created. Funnily enough, it has been named /media. This directory contains subdirectories which are used as mount points for removeable media such as floppy disks, cdroms and zip disks. The motivation for the creation of this directory has been that historically there have been a number of other different places used to mount removeable media such as /cdrom, /mnt or /mnt/cdrom. Placing the mount points for all removeable media directly in the root directory would potentially result in a large number of extra directories in /. Although the use of subdirectories in /mnt as a mount point has recently been common, it conflicts with a much older tradition of using /mnt directly as a temporary mount point. The following directories, or symbolic links to directories, must be in /media, if the corresponding subsystem is installed: floppy Floppy drive (optional) cdrom CD-ROM drive (optional) cdrecorder CD writer (optional) zip Zip drive (optional) On systems where more than one device exists for mounting a certain type of media, mount directories can be created by appending a digit to the name of those available above starting with '0', but the unqualified name must also exist. A compliant implementation with two CDROM drives might have /media/cdrom0 and /media/cdrom1 with /media/cdrom a symlink to either of these. Please see the section on the /mnt directory to achieve a better understanding of the process on mounting and unmounting filesystems. ----------------------------------------------------------------------------- 1.12. /mnt This is a generic mount point under which you mount your filesystems or devices. Mounting is the process by which you make a filesystem available to the system. After mounting your files will be accessible under the mount-point. This directory usually contains mount points or sub-directories where you mount your floppy and your CD. You can also create additional mount-points here if you wish. Standard mount points would include /mnt/cdrom and /mnt/floppy. There is no limitation to creating a mount-point anywhere on your system but by convention and for sheer practicality do not litter your file system with mount-points. It should be noted that some distributions like Debian allocate /floppy and /cdrom as mount points while Redhat and Mandrake puts them in /mnt/floppy and /mnt/cdrom respectively. However, it should be noted that as of FSSTND version 2.3 the purpose of this directory has changed. This directory is provided so that the system administrator may temporarily mount a filesystem as needed. The content of this directory is a local issue and should not affect the manner in which any program is run. This directory must not be used by installation programs: a suitable temporary directory not in use by the system must be used instead. ----------------------------------------------------------------------------- 1.12.1. Mounting and unmounting Before one can use a filesystem, it has to be mounted. The operating system then does various bookkeeping things to make sure that everything works. Since all files in UNIX are in a single directory tree, the mount operation will make it look like the contents of the new filesystem are the contents of an existing subdirectory in some already mounted filesystem. The mounts could be done as in the following example: $ mount /dev/hda2 /home $ mount /dev/hda3 /usr $ The mount command takes two arguments. The first one is the device file corresponding to the disk or partition containing the filesystem. The second one is the directory below which it will be mounted. After these commands the contents of the two filesystems look just like the contents of the /home and /usr directories, respectively. One would then say that ``/dev/hda2 is mounted on /home'', and similarly for /usr. To look at either filesystem, one would look at the contents of the directory on which it has been mounted, just as if it were any other directory. Note the difference between the device file, /dev/hda2, and the mounted-on directory, /home. The device file gives access to the raw contents of the disk, the mounted-on directory gives access to the files on the disk. The mounted-on directory is called the mount point. Linux supports many filesystem types. mount tries to guess the type of the filesystem. You can also use the -t fstype option to specify the type directly; this is sometimes necessary, since the heuristics mount uses do not always work. For example, to mount an MS-DOS floppy, you could use the following command: $ mount -t msdos /dev/fd0 /floppy $ The mounted-on directory need not be empty, although it must exist. Any files in it, however, will be inaccessible by name while the filesystem is mounted. (Any files that have already been opened will still be accessible. Files that have hard links from other directories can be accessed using those names.) There is no harm done with this, and it can even be useful. For instance, some people like to have /tmp and /var/tmp synonymous, and make /tmp be a symbolic link to /var/tmp. When the system is booted, before the /var filesystem is mounted, a /var/tmp directory residing on the root filesystem is used instead. When /var is mounted, it will make the /var/tmp directory on the root filesystem inaccessible. If /var/tmp didn't exist on the root filesystem, it would be impossible to use temporary files before mounting / var. If you don't intend to write anything to the filesystem, use the -r switch for mount to do a read-only mount. This will make the kernel stop any attempts at writing to the filesystem, and will also stop the kernel from updating file access times in the inodes. Read-only mounts are necessary for unwritable media, e.g., CD-ROMs. The alert reader has already noticed a slight logistical problem. How is the first filesystem (called the root filesystem, because it contains the root directory) mounted, since it obviously can't be mounted on another filesystem? Well, the answer is that it is done by magic. For more information, see the kernel source or the Kernel Hackers' Guide. The root filesystem is magically mounted at boot time, and one can rely on it to always be mounted. If the root filesystem can't be mounted, the system does not boot. The name of the filesystem that is magically mounted as root is either compiled into the kernel, or set using LILO or rdev. The root filesystem is usually first mounted read-only. The startup scripts will then run fsck to verify its validity, and if there are no problems, they will re-mount it so that writes will also be allowed. fsck must not be run on a mounted filesystem, since any changes to the filesystem while fsck is running will cause trouble. Since the root filesystem is mounted read-only while it is being checked, fsck can fix any problems without worry, since the remount operation will flush any metadata that the filesystem keeps in memory. On many systems there are other filesystems that should also be mounted automatically at boot time. These are specified in the /etc/fstab file; see the fstab man page for details on the format. The details of exactly when the extra filesystems are mounted depend on many factors, and can be configured by each administrator if need be. When a filesystem no longer needs to be mounted, it can be unmounted with umount. It should of course be unmount, but the n mysteriously disappeared in the 70s, and hasn't been seen since. Please return it to Bell Labs, NJ, if you find it. umount takes one argument: either the device file or the mount point. For example, to unmount the directories of the previous example, one could use the commands $ umount /dev/hda2 $ umount /usr $ See the man page for further instructions on how to use the command. It is imperative that you always unmount a mounted floppy. Don't just pop the floppy out of the drive! Because of disk caching, the data is not necessarily written to the floppy until you unmount it, so removing the floppy from the drive too early might cause the contents to become garbled. If you only read from the floppy, this is not very likely, but if you write, even accidentally, the result may be catastrophic. Mounting and unmounting requires super user privileges, i.e., only root can do it. The reason for this is that if any user can mount a floppy on any directory, then it is rather easy to create a floppy with, say, a Trojan horse disguised as /bin/sh, or any other often used program. However, it is often necessary to allow users to use floppies, and there are several ways to do this:   * Give the users the root password. This is obviously bad security, but is the easiest solution. It works well if there is no need for security anyway, which is the case on many non-networked, personal systems.   * Use a program such as sudo to allow users to use mount. This is still bad security, but doesn't directly give super user privileges to everyone. [1]   * Make the users use mtools, a package for manipulating MS-DOS filesystems, without mounting them. This works well if MS-DOS floppies are all that is needed, but is rather awkward otherwise.   * List the floppy devices and their allowable mount points together with the suitable options in /etc/fstab. The last alternative can be implemented by adding a line like the following to the /etc/fstab file: /dev/fd0 /floppy msdos user,noauto 0 0 The columns are: device file to mount, directory to mount on, filesystem type, options, backup frequency (used by dump), and fsck pass number (to specify the order in which filesystems should be checked upon boot; 0 means no check). The noauto option stops this mount to be done automatically when the system is started (i.e., it stops mount -a from mounting it). The user option allows any user to mount the filesystem, and, because of security reasons, disallows execution of programs (normal or setuid) and interpretation of device files from the mounted filesystem. After this, any user can mount a floppy with an msdos filesystem with the following command: $ mount /floppy $ The floppy can (and needs to, of course) be unmounted with the corresponding umount command. If you want to provide access to several types of floppies, you need to give several mount points. The settings can be different for each mount point. For example, to give access to both MS-DOS and ext2 floppies, you could have the following to lines in /etc/fstab: /dev/fd0 /dosfloppy msdos user,noauto 0 0 /dev/fd0 /ext2floppy ext2 user,noauto 0 0 For MS-DOS filesystems (not just floppies), you probably want to restrict access to it by using the uid, gid, and umask filesystem options, described in detail on the mount manual page. If you aren't careful, mounting an MS-DOS filesystem gives everyone at least read access to the files in it, which is not a good idea. ----------------------------------------------------------------------------- 1.13. /opt This directory is reserved for all the software and add-on packages that are not part of the default installation. For example, StarOffice, Kylix, Netscape Communicator and WordPerfect packages are normally found here. To comply with the FSSTND, all third party applications should be installed in this directory. Any package to be installed here must locate its static files (ie. extra fonts, clipart, database files) must locate its static files in a separate /opt/'package' or /opt/'provider' directory tree (similar to the way in which Windows will install new software to its own directory tree C:\ Windows\Progam Files\"Program Name"), where 'package' is a name that describes the software package and 'provider' is the provider's LANANA registered name. Although most distributions neglect to create the directories /opt/bin, / opt/doc, /opt/include, /opt/info, /opt/lib, and /opt/man they are reserved for local system administrator use. Packages may provide "front-end" files intended to be placed in (by linking or copying) these reserved directories by the system administrator, but must function normally in the absence of these reserved directories. Programs to be invoked by users are located in the directory /opt/'package'/bin. If the package includes UNIX manual pages, they are located in /opt/'package'/man and the same substructure as /usr/ share/man must be used. Package files that are variable must be installed in /var/opt. Host-specific configuration files are installed in /etc/opt. Under no circumstances are other package files to exist outside the /opt, / var/opt, and /etc/opt hierarchies except for those package files that must reside in specific locations within the filesystem tree in order to function properly. For example, device lock files in /var/lock and devices in /dev. Distributions may install software in /opt, but must not modify or delete software installed by the local system administrator without the assent of the local system administrator. The use of /opt for add-on software is a well-established practice in the UNIX community. The System V Application Binary Interface [AT&T 1990], based on the System V Interface Definition (Third Edition) and the Intel Binary Compatibility Standard v. 2 (iBCS2) provides for an /opt structure very similar to the one defined here. Generally, all data required to support a package on a system must be present within /opt/'package', including files intended to be copied into / etc/opt/'package' and /var/opt/'package' as well as reserved directories in / opt. The minor restrictions on distributions using /opt are necessary because conflicts are possible between distribution installed and locally installed software, especially in the case of fixed pathnames found in some binary software. The structure of the directories below /opt/'provider' is left up to the packager of the software, though it is recommended that packages are installed in /opt/'provider'/'package' and follow a similar structure to the guidelines for /opt/package. A valid reason for diverging from this structure is for support packages which may have files installed in /opt/ 'provider'/ lib or /opt/'provider'/bin. ----------------------------------------------------------------------------- 1.14. /proc /proc is very special in that it is also a virtual filesystem. It's sometimes referred to as a process information pseudo-file system. It doesn't contain 'real' files but runtime system information (e.g. system memory, devices mounted, hardware configuration, etc). For this reason it can be regarded as a control and information centre for the kernel. In fact, quite a lot of system utilities are simply calls to files in this directory. For example, 'lsmod' is the same as 'cat /proc/modules' while 'lspci' is a synonym for 'cat /proc/pci'. By altering files located in this directory you can even read/change kernel parameters (sysctl) while the system is running. The most distinctive thing about files in this directory is the fact that all of them have a file size of 0, with the exception of kcore, mtrr and self. A directory listing looks similar to the following: total 525256 dr-xr-xr-x 3 root root 0 Jan 19 15:00 1 dr-xr-xr-x 3 daemon root 0 Jan 19 15:00 109 dr-xr-xr-x 3 root root 0 Jan 19 15:00 170 dr-xr-xr-x 3 root root 0 Jan 19 15:00 173 dr-xr-xr-x 3 root root 0 Jan 19 15:00 178 dr-xr-xr-x 3 root root 0 Jan 19 15:00 2 dr-xr-xr-x 3 root root 0 Jan 19 15:00 3 dr-xr-xr-x 3 root root 0 Jan 19 15:00 4 dr-xr-xr-x 3 root root 0 Jan 19 15:00 421 dr-xr-xr-x 3 root root 0 Jan 19 15:00 425 dr-xr-xr-x 3 root root 0 Jan 19 15:00 433 dr-xr-xr-x 3 root root 0 Jan 19 15:00 439 dr-xr-xr-x 3 root root 0 Jan 19 15:00 444 dr-xr-xr-x 3 daemon daemon 0 Jan 19 15:00 446 dr-xr-xr-x 3 root root 0 Jan 19 15:00 449 dr-xr-xr-x 3 root root 0 Jan 19 15:00 453 dr-xr-xr-x 3 root root 0 Jan 19 15:00 456 dr-xr-xr-x 3 root root 0 Jan 19 15:00 458 dr-xr-xr-x 3 root root 0 Jan 19 15:00 462 dr-xr-xr-x 3 root root 0 Jan 19 15:00 463 dr-xr-xr-x 3 root root 0 Jan 19 15:00 464 dr-xr-xr-x 3 root root 0 Jan 19 15:00 465 dr-xr-xr-x 3 root root 0 Jan 19 15:00 466 dr-xr-xr-x 3 root root 0 Jan 19 15:00 467 dr-xr-xr-x 3 gdm gdm 0 Jan 19 15:00 472 dr-xr-xr-x 3 root root 0 Jan 19 15:00 483 dr-xr-xr-x 3 root root 0 Jan 19 15:00 5 dr-xr-xr-x 3 root root 0 Jan 19 15:00 6 dr-xr-xr-x 3 root root 0 Jan 19 15:00 7 dr-xr-xr-x 3 root root 0 Jan 19 15:00 8 -r--r--r-- 1 root root 0 Jan 19 15:00 apm dr-xr-xr-x 3 root root 0 Jan 19 15:00 bus -r--r--r-- 1 root root 0 Jan 19 15:00 cmdline -r--r--r-- 1 root root 0 Jan 19 15:00 cpuinfo -r--r--r-- 1 root root 0 Jan 19 15:00 devices -r--r--r-- 1 root root 0 Jan 19 15:00 dma dr-xr-xr-x 3 root root 0 Jan 19 15:00 driver -r--r--r-- 1 root root 0 Jan 19 15:00 execdomains -r--r--r-- 1 root root 0 Jan 19 15:00 fb -r--r--r-- 1 root root 0 Jan 19 15:00 filesystems dr-xr-xr-x 2 root root 0 Jan 19 15:00 fs dr-xr-xr-x 4 root root 0 Jan 19 15:00 ide -r--r--r-- 1 root root 0 Jan 19 15:00 interrupts -r--r--r-- 1 root root 0 Jan 19 15:00 iomem -r--r--r-- 1 root root 0 Jan 19 15:00 ioports dr-xr-xr-x 18 root root 0 Jan 19 15:00 irq -r-------- 1 root root 536809472 Jan 19 15:00 kcore -r-------- 1 root root 0 Jan 19 14:58 kmsg -r--r--r-- 1 root root 0 Jan 19 15:00 ksyms -r--r--r-- 1 root root 0 Jan 19 15:00 loadavg -r--r--r-- 1 root root 0 Jan 19 15:00 locks -r--r--r-- 1 root root 0 Jan 19 15:00 mdstat -r--r--r-- 1 root root 0 Jan 19 15:00 meminfo -r--r--r-- 1 root root 0 Jan 19 15:00 misc -r--r--r-- 1 root root 0 Jan 19 15:00 modules -r--r--r-- 1 root root 0 Jan 19 15:00 mounts -rw-r--r-- 1 root root 137 Jan 19 14:59 mtrr dr-xr-xr-x 3 root root 0 Jan 19 15:00 net dr-xr-xr-x 2 root root 0 Jan 19 15:00 nv -r--r--r-- 1 root root 0 Jan 19 15:00 partitions -r--r--r-- 1 root root 0 Jan 19 15:00 pci dr-xr-xr-x 4 root root 0 Jan 19 15:00 scsi lrwxrwxrwx 1 root root 64 Jan 19 14:58 self -> 483 -rw-r--r-- 1 root root 0 Jan 19 15:00 slabinfo -r--r--r-- 1 root root 0 Jan 19 15:00 stat -r--r--r-- 1 root root 0 Jan 19 15:00 swaps dr-xr-xr-x 10 root root 0 Jan 19 15:00 sys dr-xr-xr-x 2 root root 0 Jan 19 15:00 sysvipc dr-xr-xr-x 4 root root 0 Jan 19 15:00 tty -r--r--r-- 1 root root 0 Jan 19 15:00 uptime -r--r--r-- 1 root root 0 Jan 19 15:00 version Each of the numbered directories corresponds to an actual process ID. Looking at the process table, you can match processes with the associated process ID. For example, the process table might indicate the following for the secure shell server: # ps ax | grep sshd 439 ? S 0:00 /usr/sbin/sshd Details of this process can be obtained by looking at the associated files in the directory for this process, /proc/460. You might wonder how you can see details of a process that has a file size of 0. It makes more sense if you think of it as a window into the kernel. The file doesn't actually contain any data; it just acts as a pointer to where the actual process information resides. For example, a listing of the files in the /proc/460 directory looks similar to the following: total 0 -r--r--r-- 1 root root 0 Jan 19 15:02 cmdline lrwxrwxrwx 1 root root 0 Jan 19 15:02 cwd -> / -r-------- 1 root root 0 Jan 19 15:02 environ lrwxrwxrwx 1 root root 0 Jan 19 15:02 exe -> /usr/sbin/sshd dr-x------ 2 root root 0 Jan 19 15:02 fd -r--r--r-- 1 root root 0 Jan 19 15:02 maps -rw------- 1 root root 0 Jan 19 15:02 mem lrwxrwxrwx 1 root root 0 Jan 19 15:02 root -> / -r--r--r-- 1 root root 0 Jan 19 15:02 stat -r--r--r-- 1 root root 0 Jan 19 15:02 statm -r--r--r-- 1 root root 0 Jan 19 15:02 status The purpose and contents of each of these files is explained below: /proc/PID/cmdline Command line arguments. /proc/PID/cpu Current and last cpu in which it was executed. /proc/PID/cwd Link to the current working directory. /proc/PID/environ Values of environment variables. /proc/PID/exe Link to the executable of this process. /proc/PID/fd Directory, which contains all file descriptors. /proc/PID/maps Memory maps to executables and library files. /proc/PID/mem Memory held by this process. /proc/PID/root Link to the root directory of this process. /proc/PID/stat Process status. /proc/PID/statm Process memory status information. /proc/PID/status Process status in human readable form. Should you wish to know more, the man page for proc describes each of the files associated with a running process ID in far greater detail. Even though files appear to be of size 0, examining their contents reveals otherwise: # cat status Name: sshd State: S (sleeping) Tgid: 439 Pid: 439 PPid: 1 TracerPid: 0 Uid: 0 0 0 0 Gid: 0 0 0 0 FDSize: 32 Groups: VmSize: 2788 kB VmLck: 0 kB VmRSS: 1280 kB VmData: 252 kB VmStk: 16 kB VmExe: 268 kB VmLib: 2132 kB SigPnd: 0000000000000000 SigBlk: 0000000000000000 SigIgn: 8000000000001000 SigCgt: 0000000000014005 CapInh: 0000000000000000 CapPrm: 00000000fffffeff CapEff: 00000000fffffeff The files in the /proc directory act very similar to the process ID subdirectory files. For example, examining the contents of the /proc/ interrupts file displays something like the following: # cat interrupts CPU0 0: 32657 XT-PIC timer 1: 1063 XT-PIC keyboard 2: 0 XT-PIC cascade 8: 3 XT-PIC rtc 9: 0 XT-PIC cmpci 11: 332 XT-PIC nvidia 14: 5289 XT-PIC ide0 15: 13 XT-PIC ide1 NMI: 0 ERR: 0 Each of the numbers down the left-hand column represents the interrupt that is in use. Examining the contents of the file dynamically gathers the associated data and displays it to the screen. Most of the /proc file system is read-only; however, some files allow kernel variable to be changed. This provides a mechanism to actually tune the kernel without recompiling and rebooting. The procinfo utility summarizes /proc file system information into a display similar to the following: # /usr/bin/procinfo Linux 2.4.18 (root@DEB) (gcc 2.95.4 20011002 ) #2 1CPU [DEB.(none)] Memory: Total Used Free Shared Buffers Cached Mem: 513908 107404 406504 0 2832 82180 Swap: 265032 0 265032 Bootup: Sun Jan 19 14:58:27 2003 Load average: 0.29 0.13 0.05 1/30 566 user : 0:00:10.26 2.3% page in : 74545 disk 1: 6459r 796w nice : 0:00:00.00 0.0% page out: 9416 disk 2: 19r 0w system: 0:00:19.55 4.5% swap in : 1 idle : 0:06:48.30 93.2% swap out: 0 uptime: 0:07:18.11 context : 22059 irq 0: 43811 timer irq 9: 0 cmpci irq 1: 1427 keyboard irq 11: 332 nvidia irq 2: 0 cascade [4] irq 12: 2 irq 6: 2 irq 14: 7251 ide0 irq 8: 3 rtc irq 15: 83 ide1 /proc/apm Advanced power management info. /proc/bus Directory containing bus specific information. /proc/cmdline Kernel command line. /proc/cpuinfo Information about the processor, such as its type, make, model, and performance. /proc/devices List of device drivers configured into the currently running kernel (block and character). /proc/dma Shows which DMA channels are being used at the moment. /proc/driver Various drivers grouped here, currently rtc /proc/execdomains Execdomains, related to security. /proc/fb Frame Buffer devices. /proc/filesystems Filesystems configured/supported into/by the kernel. /proc/fs File system parameters, currently nfs/exports. /proc/ide This subdirectory contains information about all IDE devices of which the kernel is aware. There is one subdirectory for each IDE controller, the file drivers and a link for each IDE device, pointing to the device directory in the controller-specific subtree. The file drivers contains general information about the drivers used for the IDE devices. More detailed information can be found in the controller-specific subdirectories. These are named ide0, ide1 and so on. Each of these directories contains the files shown here: /proc/ide/ide?/channel IDE channel (0 or 1) /proc/ide/ide?/config Configuration (only for PCI/IDE bridge) /proc/ide/ide?/mate Mate name (onchip partnered controller) /proc/ide/ide?/model Type/Chipset of IDE controller Each device connected to a controller has a separate subdirectory in the controllers directory. The following files listed are contained in these directories: /proc/ide/ide?/model/cache The cache. /proc/ide/ide?/model/capacity Capacity of the medium (in 512Byte blocks) /proc/ide/ide?/model/driver driver and version /proc/ide/ide?/model/geometry physical and logical geometry /proc/ide/ide?/model/identify device identify block /proc/ide/ide?/model/media media type /proc/ide/ide?/model/model device identifier /proc/ide/ide?/model/settings device setup /proc/ide/ide?/model/smart_thresholds IDE disk management thresholds /proc/ide/ide?/model/smart_values IDE disk management values /proc/interrupts Shows which interrupts are in use, and how many of each there have been. You can, for example, check which interrupts are currently in use and what they are used for by looking in the file /proc/interrupts: # cat /proc/interrupts CPU0 0: 8728810 XT-PIC timer 1: 895 XT-PIC keyboard 2: 0 XT-PIC cascade 3: 531695 XT-PIC aha152x 4: 2014133 XT-PIC serial 5: 44401 XT-PIC pcnet_cs 8: 2 XT-PIC rtc 11: 8 XT-PIC i82365 12: 182918 XT-PIC PS/2 Mouse 13: 1 XT-PIC fpu 14: 1232265 XT-PIC ide0 15: 7 XT-PIC ide1 NMI: 0 In 2.4 based kernels a couple of lines were added to this file LOC & ERR (this is the output of an SMP machine): # cat /proc/interrupts CPU0 CPU1 0: 1243498 1214548 IO-APIC-edge timer 1: 8949 8958 IO-APIC-edge keyboard 2: 0 0 XT-PIC cascade 5: 11286 10161 IO-APIC-edge soundblaster 8: 1 0 IO-APIC-edge rtc 9: 27422 27407 IO-APIC-edge 3c503 12: 113645 113873 IO-APIC-edge PS/2 Mouse 13: 0 0 XT-PIC fpu 14: 22491 24012 IO-APIC-edge ide0 15: 2183 2415 IO-APIC-edge ide1 17: 30564 30414 IO-APIC-level eth0 18: 177 164 IO-APIC-level bttv NMI: 2457961 2457959 LOC: 2457882 2457881 ERR: 2155 NMI is incremented in this case because every timer interrupt generates a NMI (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lookups. LOC is the local interrupt counter of the internal APIC of every CPU. ERR is incremented in the case of errors in the IO-APIC bus (the bus that connects the CPUs in an SMP system. This means that an error has been detected, the IO-APIC automatically retries the transmission, so it should not be a big problem, but you should read the SMP-FAQ. In this context it could be interesting to note the new irq directory in 2.4. It could be used to set IRQ to CPU affinity, this means that you can "hook" an IRQ to only one CPU, or to exclude a CPU from handling IRQs. The contents of the irq subdir is one subdir for each IRQ, and one file; prof_cpu_mask. For example, # ls /proc/irq/ 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask 1 11 13 15 17 19 3 5 7 9 # ls /proc/irq/0/ smp_affinity The contents of the prof_cpu_mask file and each smp_affinity file for each IRQ is the same by default: # cat /proc/irq/0/smp_affinity ffffffff It's a bitmask, in which you can specify which CPUs can handle the IRQ, you can set it by doing: # echo 1 > /proc/irq/prof_cpu_mask This means that only the first CPU will handle the IRQ, but you can also echo 5 which means that only the first and fourth CPU can handle the IRQ. The way IRQs are routed is handled by the IO-APIC, and its Round Robin between all the CPUs which are allowed to handle it. As usual the kernel has more info than you and does a better job than you, so the defaults are the best choice for almost everyone. /proc/iomem Memory map. /proc/ioports Which I/O ports are in use at the moment. /proc/irq Masks for irq to cpu affinity. /proc/isapnp ISA PnP (Plug&Play) Info. /proc/kcore An image of the physical memory of the system (can be ELF or A.OUT (deprecated in 2.4)). This is exactly the same size as your physical memory, but does not really take up that much memory; it is generated on the fly as programs access it. (Remember: unless you copy it elsewhere, nothing under /proc takes up any disk space at all.) /proc/kmsg Messages output by the kernel. These are also routed to syslog. /proc/ksyms Kernel symbol table. /proc/loadavg The 'load average' of the system; three indicators of how much work the system has done during the last 1, 5 & 15 minutes. /proc/locks Kernel locks. /proc/meminfo Information about memory usage, both physical and swap. Concatenating this file produces similar results to using 'free' or the first few lines of 'top'. /proc/misc Miscellaneous pieces of information. This is for information that has no real place within the rest of the proc filesystem. /proc/modules Kernel modules currently loaded. Typically its output is the same as that given by the 'lsmod' command. /proc/mounts Mounted filesystems /proc/mtrr Information regarding mtrrs. (On Intel P6 family processors (Pentium Pro, Pentium II and later) the Memory Type Range Registers (MTRRs) may be used to control processor access to memory ranges. This is most useful when you have a video (VGA) card on a PCI or AGP bus. Enabling write-combining allows bus write transfers to be combined into a larger transfer before bursting over the PCI/AGP bus. This can increase performance of image write operations 2.5 times or more. The Cyrix 6x86, 6x86MX and M II processors have Address Range Registers (ARRs) which provide a similar functionality to MTRRs. For these, the ARRs are used to emulate the MTRRs. The AMD K6-2 (stepping 8 and above) and K6-3 processors have two MTRRs. These are supported. The AMD Athlon family provide 8 Intel style MTRRs. The Centaur C6 (WinChip) has 8 MCRs, allowing write-combining. These are also supported. The VIA Cyrix III and VIA C3 CPUs offer 8 Intel style MTRRs.) For more details regarding mtrr technology see /usr/src/ linux/Documentation/mtrr.txt. /proc/net Status information about network protocols. IPv6 information /proc/net/udp6 UDP sockets (IPv6). /proc/net/tcp6 TCP sockets (IPv6). /proc/net/raw6 Raw device statistics (IPv6). /proc/net/igmp6 IP multicast addresses, which this host joined (IPv6). /proc/net/if_inet6 List of IPv6 interface addresses. /proc/net/ipv6_route Kernel routing table for IPv6. /proc/net/rt6_stats Global IPv6 routing tables statistics. /proc/net/sockstat6 Socket statistics (IPv6). /proc/net/snmp6 Snmp data (IPv6). General Network information /proc/net/arp Kernel ARP table. /proc/net/dev network devices with statistics. /proc/net/dev_mcast the Layer2 multicast groups which a device is listening to (interface index, label, number of references, number of bound addresses). /proc/net/dev_stat network device status. /proc/net/ip_fwchains Firewall chain linkage. /proc/net/ip_fwnames Firewall chain names. /proc/net/ip_masq Directory containing the masquerading tables. /proc/net/ip_masquerade Major masquerading table. /proc/net/netstat Network statistics. /proc/net/raw raw device statistics. /proc/net/route Kernel routing table. /proc/net/rpc Directory containing rpc info. /proc/net/rt_cache Routing cache. /proc/net/snmp SNMP data. /proc/net/sockstat Socket statistics. /proc/net/tcp TCP sockets. /proc/net/tr_rif Token ring RIF routing table. /proc/net/udp UDP sockets. /proc/net/unix UNIX domain sockets. /proc/net/wireless Wireless interface data (Wavelan etc). /proc/net/igmp IP multicast addresses, which this host joined. /proc/net/psched Global packet scheduler parameters. /proc/net/netlink List of PF_NETLINK sockets. /proc/net/ip_mr_vifs List of multicast virtual interfaces. /proc/net/ip_mr_cache List of multicast routing cache. You can use this information to see which network devices are available in your system and how much traffic was routed over those devices. In addition, each Channel Bond interface has its own directory. For example, the bond0 device will have a directory called /proc/net/bond0/. It will contain information that is specific to that bond, such as the current slaves of the bond, the link status of the slaves, and how many times the slaves link has failed. /proc/parport The directory /proc/parport contains information about the parallel ports of your system. It has one subdirectory for each port, named after the port number (0,1,2,...). /proc/parport/autoprobe Any IEEE-1284 device ID information that has been acquired. /proc/parport/devices list of the device drivers using that port. A + will appear by the name of the device currently using the port (it might not appear against any). /proc/parport/hardware Parallel port's base address, IRQ line and DMA channel. /proc/parport/irq IRQ that parport is using for that port. This is in a separate file to allow you to alter it by writing a new value in (IRQ number or none). /proc/partitions Table of partitions known to the system /proc/pci, /proc/bus/pci Depreciated info of PCI bus. /proc/rtc Real time clock /proc/scsi If you have a SCSI host adapter in your system, you'll find a subdirectory named after the driver for this adapter in /proc/scsi. You'll also see a list of all recognized SCSI devices in /proc/scsi. The directory named after the driver has one file for each adapter found in the system. These files contain information about the controller, including the used IRQ and the IO address range. The amount of information shown is dependent on the adapter you use. /proc/self A symbolic link to the process directory of the program that is looking at /proc. When two processes look at /proc, they get different links. This is mainly a convenience to make it easier for programs to get at their process directory. /proc/slabinfo The slabinfo file gives information about memory usage at the slab level. Linux uses slab pools for memory management above page level in version 2.2. Commonly used objects have their own slab pool (such as network buffers, directory cache, and so on). /proc/stat Overall/various statistics about the system, such as the number of page faults since the system was booted. /proc/swaps Swap space utilization /proc/sys This is not only a source of information, it also allows you to change parameters within the kernel without the need for recompilation or even a system reboot. Take care when attempting this as it can both optimize your system and also crash it. It is advisable to read both documentation and source before actually making adjustments. The entries in /proc may change slightly between kernel versions, so if there is any doubt review the kernel documentation in the directory /usr/src/linux/Documentation. Under some circumstances, you may have no alternative but to reboot the machine once an error occurs. To change a value, simply echo the new value into the file. An example is given below in the section on the file system data. Of course, you need to be 'root' to do any of this. You can create your own boot script to perform this every time your system boots. /proc/sys/fs Contains file system data. This subdirectory contains specific file system, file handle, inode, dentry and quota information. dentry-state Status of the directory cache. Since directory entries are dynamically allocated and deallocated, this file indicates the current status. It holds six values, in which the last two are not used and are always zero. The others are listed below: File Content nr_dentry Almost always zero nr_unused Number of unused cache entries age_limit in seconds after the entry may be reclaimed, when memory is short want_pages internally dquot-max The file dquot-max shows the maximum number of cached disk quota entries. dquot-nr shows the number of allocated disk quota entries and the number of free disk quota entries. If the number of available cached disk quotas is very low and you have a large number of simultaneous system users, you might want to raise the limit. file-nr and file-max The kernel allocates file handles dynamically, but doesn't free them again at this time. The value in file-max denotes the maximum number of file handles that the Linux kernel will allocate. When you get a lot of error messages about running out of file handles, you might want to raise this limit. The default value is 4096. To change it, just write the new number into the file: # cat /proc/sys/fs/file-max 4096 # echo 8192 > /proc/sys/fs/file-max # cat /proc/sys/fs/file-max 8192 This method of revision is useful for all customizable parameters of the kernel - simply echo the new value to the corresponding file. The three values in file-nr denote the number of allocated file handles, the number of used file handles, and the maximum number of file handles. When the allocated file handles come close to the maximum, but the number of actually used handles is far behind, you've encountered a peak in your usage of file handles and you don't need to increase the maximum. inode-state, inode-nr and inode-max As with file handles, the kernel allocates the inode structures dynamically, but can't free them yet. The value in inode-max denotes the maximum number of inode handlers. This value should be 3 to 4 times larger than the value in file-max, since stdin, stdout, and network sockets also need an inode struct to handle them. If you regularly run out of inodes, you should increase this value. The file inode-nr contains the first two items from inode-state, so we'll skip to that file... inode-state contains three actual numbers and four dummy values. The numbers are nr_inodes, nr_free_inodes, and preshrink (in order of appearance). nr_inodes Denotes the number of inodes the system has allocated. This can be slightly more than inode-max because Linux allocates them one pageful at a time. nr_free_inodes Represents the number of free inodes and preshrink is nonzero when nr_inodes is greater than inode-max and the system needs to prune the inode list instead of allocating more. super-nr and super-max Again, super block structures are allocated by the kernel, but not freed. The file super-max contains the maximum number of super block handlers, where super-nr shows the number of currently allocated ones. Every mounted file system needs a super block, so if you plan to mount lots of file systems, you may want to increase these numbers. binfmt_misc This handles the kernel support for miscellaneous binary formats. binfmt_misc provides the ability to register additional binary formats to the kernel without compiling an additional module/kernel. Therefore, binfmt_misc needs to know magic numbers at the beginning or the filename extension of the binary. It works by maintaining a linked list of structs that contain a description of a binary format, including a magic with size (or the filename extension), offset and mask, and the interpreter name. On request it invokes the given interpreter with the original program as argument, as binfmt_java and binfmt_em86 and binfmt_mz do. Since binfmt_misc does not define any default binary-formats, you have to register an additional binary-format. There are two general files in binfmt_misc and one file per registered format. The two general files are register and status. To register a new binary format you have to issue the command echo :name:type:offset:magic:mask:interpreter: > /proc/sys/fs/ binfmt_misc/register with appropriate name (the name for the / proc-dir entry), offset (defaults to 0, if omitted), magic, mask (which can be omitted, defaults to all 0xff) and last but not least, the interpreter that is to be invoked (for example and testing /bin/ echo). Type can be M for usual magic matching or E for filename extension matching (give extension in place of magic). If you do a cat on the file /proc/sys/fs/binfmt_misc/status, you will get the current status (enabled/disabled) of binfmt_misc. Change the status by echoing 0 (disables) or 1 (enables) or -1 (caution: this clears all previously registered binary formats) to status. For example echo 0 > status to disable binfmt_misc (temporarily). Each registered handler has an entry in /proc/sys/fs/binfmt_misc. These files perform the same function as status, but their scope is limited to the actual binary format. By 'cating' this file, you also receive all related information about the interpreter/magic of the binfmt. An example of the usage of binfmt_misc (emulate binfmt_java) follows: cd /proc/sys/fs/binfmt_misc echo ':Java:M::\xca\xfe\xba\xbe::/usr/local/java/bin/javawrapper:' > register echo ':HTML:E::html::/usr/local/java/bin/appletviewer:' > register echo ':Applet:M::