limits.conf - configuration file for the pam_limits module
The pam_limits.so module applies ulimit limits, nice priority and number of simultaneous login sessions limit to user login sessions. This description of the configuration file syntax applies to the /etc/security/limits.conf file and *.conf files in the /etc/security/limits.d directory.
The syntax of the lines is as follows:
<domain> <type> <item> <value>
The fields listed above should be filled as follows:
NOTE: group and wildcard limits are not applied to the root user. To set a limit for the root user, this field must contain the literal username root.
Note, if you specify a type of '-' but neglect to supply the item and value fields then the module will never enforce any limits on the specified user/group etc. .
All items support the values -1, unlimited or infinity indicating no limit, except for priority, nice, and nonewprivs. If nofile is to be set to one of these values, it will be set to the contents of /proc/sys/fs/nr_open instead (see setrlimit(3)).
If a hard limit or soft limit of a resource is set to a valid value, but outside of the supported range of the local system, the system may reject the new limit or unexpected behavior may occur. If the control value required is used, the module will reject the login if a limit could not be set.
In general, individual limits have priority over group limits, so if you impose no limits for admin group, but one of the members in this group have a limits line, the user will have its limits set according to this line.
Also, please note that all limit settings are set per login. They are not global, nor are they permanent; existing only for the duration of the session. One exception is the maxlogin option, this one is system wide. But there is a race, concurrent logins at the same time will not always be detect as such but only counted as one.
In the limits configuration file, the '#' character introduces a comment - after which the rest of the line is ignored.
The pam_limits module does report configuration problems found in its configuration file and errors via syslog(3).
These are some example lines which might be specified in /etc/security/limits.conf.
* soft core 0 root hard core 100000 * hard nofile 512 @student hard nproc 20 @faculty soft nproc 20 @faculty hard nproc 50 ftp hard nproc 0 @student - maxlogins 4 @student - nonewprivs 1 :123 hard cpu 5000 @500: soft cpu 10000 600:700 hard locks 10
pam_limits was initially written by Cristian Gafton <email@example.com>