limits.conf - configuration file for the pam_limits module,

/etc/security/limits.conf

The syntax of the lines:

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

The fields listed above should be filled as follows:

<domain>

• A username
• A groupname, with @group syntax. This should not be confused with netgroups.
• The wildcard *, for default entry.
• The wildcard %, for maxlogins limit only, can also be used with %group syntax.

<type>

hard	for enforcing hard resource limits. These limits are set by the superuser and enforced by the Kernel. The user cannot raise his requirement of system resources above such values.
soft	for enforcing soft resource limits. These limits are ones that the user can move up or down within the permitted range by any pre-exisiting hard limits. The values specified with this token can be thought of as default values, for normal system usage.
-	for enforcing both soft and hard resource limits together.

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.

<item>

core	limits the core file size (KB)
data	maximum data size (KB)
fsize	maximum filesize (KB)
memlock	maximum locked-in-memory address space (KB)
nofile	maximum number of open files
rss	maximum resident set size (KB)
stack	maximum stack size (KB)
cpu	maximum CPU time (minutes)
nproc	maximum number of processes as address space limit
maxlogins	maximum number of logins for this user
maxsyslogins	maximum number of logins on system
priority	the priority to run user process with (negative values boost process priority)
locks	maximum locked files (Linux 2.4 and higher)
sigpending	maximum number of pending signals (Linux 2.6 and higher)
msqqueue	maximum memory used by POSIX message queues (bytes) (Linux 2.6 and higher)
nice	maximum nice priority allowed to raise to (Linux 2.6.12 and higher)
rtprio	maximum realtime priority allowed for non-privileged processes (Linux 2.6.12 and higher)

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).

Examples

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

# Feel the city breakin and everybody shakin, and we’re stayin alive, stayin alive # ~ The Bee Gees

Related Linux commands

/etc/security/limits.conf
quota - Display disk usage and limits.
ulimit - Control the resources available to a process.
Fork bomb - unixmen.com
pam_limits(8), pam.d(5), pam(8).