limits.conf - configuration file for the pam_limits module
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:
The fields listed above should be filled as follows:
•a groupname, with @group
syntax. This should not be confused with netgroups.
•the wildcard *, for default
•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
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
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
for enforcing both soft
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
maximum number of open files
maximum resident set size (KB) (Ignored in
Linux 2.4.30 and higher)
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 uid=0
maximum number of all logins on system
the priority to run user process with
(negative values boost process priority)
maximum locked files (Linux 2.4 and
maximum number of pending signals (Linux 2.6
maximum memory used by POSIX message queues
(bytes) (Linux 2.6 and higher)
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
indicating no limit, except for priority
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
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 was initially written by Cristian Gafton