ulimit - set or get resource usage limits


ulimit [OPTIONS] [LIMIT]


ulimit sets or outputs the resource usage limits of the shell and any processes spawned by it. If a new limit value is omitted, the current value of the limit of the resource is printed; otherwise, the specified limit is set to the new value.

Use one of the following switches to specify which resource limit to set or report:

-b or --socket-buffers

The maximum size of socket buffers.

-c or --core-size

The maximum size of core files created. By setting this limit to zero, core dumps can be disabled.

-d or --data-size

The maximum size of a process’ data segment.

-e or --nice

Controls the maximum nice value; on Linux, this value is subtracted from 20 to give the effective value.

-f or --file-size

The maximum size of files created by a process.

-i or --pending-signals

The maximum number of signals that may be queued.

-l or --lock-size

The maximum size that may be locked into memory.

-m or --resident-set-size

The maximum resident set size.

-n or --file-descriptor-count

The maximum number of open file descriptors.

-q or --queue-size

The maximum size of data in POSIX message queues.

-r or --realtime-priority

The maximum realtime scheduling priority.

-s or --stack-size

The maximum stack size.

-t or --cpu-time

The maximum amount of CPU time in seconds.

-u or --process-count

The maximum number of processes available to the current user.

-w or --swap-size

The maximum swap space available to the current user.

-v or --virtual-memory-size

The maximum amount of virtual memory available to the shell.

-y or --realtime-maxtime

The maximum contiguous realtime CPU time in microseconds.

-K or --kernel-queues

The maximum number of kqueues (kernel queues) for the current user.

-P or --ptys

The maximum number of pseudo-terminals for the current user.

-T or --threads

The maximum number of simultaneous threads for the current user.

Note that not all these limits are available in all operating systems; consult the documentation for setrlimit in your operating system.

The value of limit can be a number in the unit specified for the resource or one of the special values hard, soft, or unlimited, which stand for the current hard limit, the current soft limit, and no limit, respectively.

If limit is given, it is the new value of the specified resource. If no option is given, then -f is assumed. Values are in kilobytes, except for -t, which is in seconds and -n and -u, which are unscaled values. The exit status is 0 unless an invalid option or argument is supplied, or an error occurs while setting a new limit.

ulimit also accepts the following options that determine what type of limit to set:

-H or --hard

Sets hard resource limit.

-S or --soft

Sets soft resource limit.

A hard limit can only be decreased. Once it is set it cannot be increased; a soft limit may be increased up to the value of the hard limit. If neither -H nor -S is specified, both the soft and hard limits are updated when assigning a new limit value, and the soft limit is used when reporting the current value.

The following additional options are also understood by ulimit:

-a or --all

Prints all current limits.

-h or --help

Displays help about using this command.

The fish implementation of ulimit should behave identically to the implementation in bash, except for these differences:

  • Fish ulimit supports GNU-style long options for all switches.

  • Fish ulimit does not support the -p option for getting the pipe size. The bash implementation consists of a compile-time check that empirically guesses this number by writing to a pipe and waiting for SIGPIPE. Fish does not do this because this method of determining pipe size is unreliable. Depending on bash version, there may also be further additional limits to set in bash that do not exist in fish.

  • Fish ulimit does not support getting or setting multiple limits in one command, except reporting all values using the -a switch.


ulimit -Hs 64 sets the hard stack size limit to 64 kB.