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
The syntax of the lines is as follows:
The fields listed above should be filled as follows:
· a username
· a groupname, with @group syntax. This should not be confused
· the wildcard *, for default entry.
· the wildcard %, for maxlogins limit only, can also be used with
%group syntax. If the % wildcard is used alone it is identical
to using * with maxsyslogins limit. With a group specified
after % it limits the total number of logins of all users that
are member of the group.
· an uid range specified as <min_uid>:<max_uid>. If min_uid is
omitted, the match is exact for the max_uid. If max_uid is
omitted, all uids greater than or equal min_uid match.
· a gid range specified as @<min_gid>:<max_gid>. If min_gid is
omitted, the match is exact for the max_gid. If max_gid is
omitted, all gids greater than or equal min_gid match. For the
exact match all groups including the user's supplementary
groups are examined. For the range matches only the user's
primary group is examined.
· a gid specified as %:<gid> applicable to maxlogins limit only.
It limits the total number of logins of all users that are
member of the group with the specified gid.
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.
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.
for enforcing soft resource limits. These limits are ones that
the user can move up or down within the permitted range by any
pre-existing 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. .
limits the core file size (KB)
maximum data size (KB)
maximum filesize (KB)
maximum locked-in-memory address space (KB)
maximum number of open files
maximum resident set size (KB) (Ignored in Linux 2.4.30 and
maximum stack size (KB)
maximum CPU time (minutes)
maximum number of processes
address space limit (KB)
maximum number of logins for this user except for this with
maximum number of all logins on system
the priority to run user process with (negative values boost
maximum locked files (Linux 2.4 and higher)
maximum number of pending signals (Linux 2.6 and higher)
maximum memory used by POSIX message queues (bytes) (Linux 2.6
maximum nice priority allowed to raise to (Linux 2.6.12 and
higher) values: [-20,19]
maximum realtime priority allowed for non-privileged processes
(Linux 2.6.12 and higher)
the directory to chroot the user to
All items support the values -1, unlimited or infinity indicating no
limit, except for priority and nice.
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
* 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
:123 hard cpu 5000
@500: soft cpu 10000
600:700 hard locks 10
pam_limits(8), pam.d(5), pam(7), getrlimit(2)getrlimit(3p)
pam_limits was initially written by Cristian Gafton <firstname.lastname@example.org>