The pam_limits PAM module sets limits on the system resources that can be obtained in a user-session. Users of uid=0 are affected by this limits, too.

By default limits are taken from the /etc/security/limits.conf config file. Then individual files from the /etc/security/limits.d/ directory are read. The files are parsed one after another in the order of "C" locale. The effect of the individual files is the same as if all the files were concatenated together in the order of parsing. If a config file is explicitely specified with a module option then the files in the above directory are not parsed.

The module must not be called by a multithreaded application.

The syntax of the lines is as follows:

<domain> <type> <item> <value>

The fields listed above should be filled as follows:

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.

In the limits configuration file, the '#' character introduces a comment - after which the rest of the line is ignored.

The pam_limits module does its best to report configuration problems found in its configuration file via syslog(3).

Only the session service is supported.

These are some example lines which might be specified in /etc/security/limits.conf.

*               soft    core            0
*               hard    rss             10000
@student        hard    nproc           20
@faculty        soft    nproc           20
@faculty        hard    nproc           50
ftp             hard    nproc           0
@student        -       maxlogins       4
    

pam_limits was initially written by Cristian Gafton <gafton@redhat.com>