Understanding /etc/security/limits.conf file

UNIX/Linux operating systems have the ability to limit the number of various system resources available to a user process. These limitations include how many files a process can have open, how large of a file the user can create, and how much memory can be used by the different components of the process such as the stack, data and text segments. ulimit is the command used to accomplish this.

To set ulimit value on a parameter use the below command.

# ulimit -p [new_value]

For the ulimits to persists across reboots we need to set the ulimit values in the configuration file /etc/security/limits.conf. Settings in /etc/security/limits.conf take the following form:

# vi /etc/security/limits.conf
#[domain]        [type]  [item]  [value]

*               -       core             [value]
*               -       data             [value]
*               -       priority         [value]
*               -       fsize            [value]
*               soft    sigpending       [value] eg:57344
*               hard    sigpending       [value] eg:57444
*               -       memlock          [value]
*               -       nofile           [value] eg:1024
*               -       msgqueue         [value] eg:819200
*               -       locks            [value]
*               soft    core             [value]
*               hard    nofile           [value]
@[group]        hard    nproc            [value]
[user]          soft    nproc            [value]
%[group]        hard    nproc            [value]
[user]          hard    nproc            [value]
@[group]        -       maxlogins        [value]
[user]          hard    cpu              [value]
[user]          soft    cpu              [value]
[user]          hard    locks            [value]

[domain] can be:

• an user name
• a group name, with @group syntax
• the wildcard *, for default entry
• the wildcard %, can be also used with %group syntax, for maxlogin limit

[type] can have the two values:

• “soft” for enforcing the soft limits
• “hard” for enforcing hard limits

[item] can be one of the following:

• core – limits the core file size (KB)
• data – max data size (KB)
• fsize – maximum filesize (KB)
• memlock – max locked-in-memory address space (KB)
• nofile – max number of open files
• rss – max resident set size (KB)
• stack – max stack size (KB)
• cpu – max CPU time (MIN)
• nproc – max number of processes
• as – address space limit (KB)
• maxlogins – max number of logins for this user
• maxsyslogins – max number of logins on the system
• priority – the priority to run user process with
• locks – max number of file locks the user can hold
• sigpending – max number of pending signals
• msgqueue – max memory used by POSIX message queues (bytes)
• nice – max nice priority allowed to raise to values: [-20, 19]
• rtprio – max realtime priority