The limits.conf file located under the /etc/security directory can be used to control and limit resources for the users on your system. It is important to set resource limits on all your
users so they can't perform denial of service attacks number of processes, amount of memory, etc). These limits will have to be set up for the user when he or she logs in. For example, limits
for all users on your system might look like this.
Edit the limits.conf file vi /etc/security/limits.conf and add or change the lines to read:
* hard core 0
* hard rss 5000
* hard nproc 20
This says to prohibit the creation of core files - core 0, restrict the number of processes to 20 - nproc 20, and restrict memory usage to 5M - rss 5000 for everyone except the super user root. All of the above only concern users who have entered through the login prompt on your system. With this kind of quota, you have more control on the processes, core files, and memory usage that users may have on your system. The asterisk * mean: all users that logs in on the server.
You must also edit the /etc/pam.d/login file and add the following line to the bottom of the file:
session required /lib/security/pam_limits.so
After adding the line above, the /etc/pam.d/login file should look like this:
#%PAM-1.0
auth required /lib/security/pam_securetty.so
auth required /lib/security/pam_pwdb.so shadow nullok
auth required /lib/security/pam_nologin.so
account required /lib/security/pam_pwdb.so
password required /lib/security/pam_cracklib.so
password required /lib/security/pam_pwdb.so nullok use_authtok md5 shadow
session required /lib/security/pam_pwdb.so
session required /lib/security/pam_limits.so
#session optional /lib/security/pam_console.so
Finally edit the /etc/profile file and change the following line:
ulimit -c 1000000
to read:
ulimit -S -c 1000000 > /dev/null 2<&1
This modification is required so as to avoid getting error messages like this Unable to reach limit during login:.