The /etc/ssh/sshd_config file is the system-wide configuration file for OpenSSH which allows you to set options that modify the operation of the daemon. This file contains keyword-value pairs, one
per line, with keywords being case insensitive. Here are the most important keywords to configure your sshd for top security; a complete listing and/or special requirements are available in the man page
for sshd(8).
Edit the sshd_config file, vi /etc/ssh/sshd_config and add/or change, if necessary, the following parameters:
# This is ssh server systemwide configuration file.
Port 22
ListenAddress 192.168.1.1
HostKey /etc/ssh/ssh_host_key
ServerKeyBits 1024
LoginGraceTime 600
KeyRegenerationInterval 3600
PermitRootLogin no
IgnoreRhosts yes
IgnoreUserKnownHosts yes
StrictModes yes
X11Forwarding no
PrintMotd yes
SyslogFacility AUTH
LogLevel INFO
RhostsAuthentication no
RhostsRSAAuthentication no
RSAAuthentication yes
PasswordAuthentication yes
PermitEmptyPasswords no
AllowUsers admin
This tells sshd_config file to set itself up for this particular configuration setup with:
Port 22
The option Port specifies on which port number ssh daemon listens for incoming connections. The default port is 22.
ListenAddress 192.168.1.1
The option ListenAddress specifies the IP address of the interface network on which the ssh daemon server socket is bind. The default is 0.0.0.0; to improve security you may specify only the required ones to limit possible addresses.
HostKey /etc/ssh/ssh_host_key
The option HostKey specifies the location containing the private host key.
ServerKeyBits 1024
The option ServerKeyBits specifies how many bits to use in the server key. These bits are used when the daemon starts to generate its RSA key.
LoginGraceTime 600
The option LoginGraceTime specifies how long in seconds after a connection request the server will wait before disconnecting if the user has not successfully logged in.
KeyRegenerationInterval 3600
The option KeyRegenerationInterval specifies how long in seconds the server should wait before automatically regenerated its key. This is a security feature to prevent decrypting captured sessions.
PermitRootLogin no
The option PermitRootLogin specifies whether root can log in using ssh. Never say yes to this option.
IgnoreRhosts yes
The option IgnoreRhosts specifies whether rhosts or shosts files should not be used in authentication. For security reasons it is recommended to no use rhosts or shosts files for authentication.
IgnoreUserKnownHosts yes
The option IgnoreUserKnownHosts specifies whether the ssh daemon should ignore the user's $HOME/.ssh/known_hosts during RhostsRSAAuthentication.
StrictModes yes
The option StrictModes specifies whether ssh should check user's permissions in their home directory and rhosts files before accepting login. This option must always be set to yes because sometimes users may accidentally leave their directory or files world-writable.
X11Forwarding no
The option X11Forwarding specifies whether X11 forwarding should be enabled or not on this server. Since we setup a server without GUI installed on it, we can safely turn this option off.
PrintMotd yes
The option PrintMotd specifies whether the ssh daemon should print the contents of the /etc/motd file when a user logs in interactively. The /etc/motd file is also known as the message of the day.
SyslogFacility AUTH
The option SyslogFacility specifies the facility code used when logging messages from sshd. The facility specifies the subsystem that produced the message--in our case, AUTH.
LogLevel INFO
The option LogLevel specifies the level that is used when logging messages from sshd. INFO is a good choice. See the man page for sshd for more information on other possibilities.
RhostsAuthentication no
The option RhostsAuthentication specifies whether sshd can try to use rhosts based authentication. Because rhosts authentication is insecure you shouldn't use this option.
RhostsRSAAuthentication no
The option RhostsRSAAuthentication specifies whether to try rhosts authentication in concert with RSA host authentication.
RSAAuthentication yes
The option RSAAuthentication specifies whether to try RSA authentication. This option must be set to yes for better security in your sessions. RSA use
public and private key pairs created with the ssh-keygen1utility for authentication purposes.
PasswordAuthentication yes
The option PasswordAuthentication specifies whether we should use password-based authentication. For strong security, this option must always be set to yes.
PermitEmptyPasswords no
The option PermitEmptyPasswords specifies whether the server allows logging in to accounts with a null password. If you intend to use the scp utility to make automatic backups over the network, you must set this option to yes.
AllowUsers admin
The option AllowUsers specifies and controls which users can access ssh services. Multiple users can be specified, separated by spaces.