|LIMITS(1)||FreeBSD General Commands Manual||LIMITS(1)|
NAMElimits — set or display process resource limits
|limits||[ -C class | -P pid | -U user][ -SHB][ -ea][ -bcdflmnstuvpw [ val]]|
|limits||[ -C class | -U user][ -SHB][ -bcdflmnstuvpw [ val]][ -E][ [ name= value ...] command]|
DESCRIPTIONThe limits utility either prints or sets kernel resource limits, and may optionally set environment variables like env(1) and run a program with the selected resources. Three uses of the limits utility are possible:
- limits [ limitflags][ name= value ...] command
- This usage sets limits according to limitflags, optionally sets environment variables given as name= value pairs, and then runs the specified command.
- limits [ limitflags]
- This usage determines values of resource settings according to limitflags, does not attempt to set them and outputs these values to standard output. By default, this will output the current kernel resource settings active for the calling process. Using the -C class or -U user options, you may also display the current resource settings modified by the appropriate login class resource limit entries from the login.conf(5) login capabilities database.
- limits -e [ limitflags]
This usage determines values of resource settings according to
limitflags, but does not set them itself. Like the previous usage, it outputs these values to standard output, except that it will emit them in
eval format, suitable for the calling shell. The calling shell is determined by examining the entries in the
/proc file system for the parent process. If the shell is known (i.e., it is one of
ulimit commands in the format understood by that shell. If the name of the shell cannot be determined, then the
ulimit format used by
sh(1) is used.
This is very useful for setting limits used by scripts, or prior launching of daemons and other background tasks with specific resource limit settings, and provides the benefit of allowing global configuration of maximum resource usage by maintaining a central database of settings in the login class database.
Within a shell script, limits will normally be used with eval within backticks as follows:
eval `limits -e -C daemon`
which causes the output of limits to be evaluated and set by the current shell.
The value of limitflags specified in the above contains one or more of the following options:
- -C class
- Use current resource values, modified by the resource entries applicable for the login class class.
- -U user
Use current resource values, modified by the resource entries applicable to the login class the
user belongs to. If user does not belong to any class, then the resource capabilities for the “
default” class are used, if it exists, or the “
root” class if the user is a superuser account.
- -P pid
- Select or set limits for the process identified by the pid.
- Select display or setting of “soft” (or current) resource limits. If specific limits settings follow this switch, only soft limits are affected unless overridden later with either the -H or -B options.
- Select display or setting of “hard” (or maximum) resource limits. If specific limits settings follow this switch, only hard limits are affected until overridden later with either the -S or -B options.
- Select display or setting of both “soft” (current) or “hard” (maximum) resource limits. If specific limits settings follow this switch, both soft and hard limits are affected until overridden later with either the -S or -H options.
- Select “eval mode” formatting for output. This is valid only on display mode and cannot be used when running a command. The exact syntax used for output depends upon the type of shell from which limits is invoked.
- -b [ val]
- Select or set the sbsize resource limit.
- -c [ val]
- Select or set (if val is specified) the coredumpsize resource limit. A value of 0 disables core dumps.
- -d [ val]
- Select or set (if val is specified) the datasize resource limit.
- -f [ val]
- Select or set the filesize resource limit.
- -l [ val]
- Select or set the memorylocked resource limit.
- -m [ val]
- Select or set the memoryuse size limit.
- -n [ val]
- Select or set the openfiles resource limit. The system-wide limit on the maximum number of open files per process can be viewed by examining the kern.maxfilesperproc sysctl(8) variable. The total number of simultaneously open files in the entire system is limited to the value displayed by the kern.maxfiles sysctl(8) variable.
- -s [ val]
- Select or set the stacksize resource limit.
- -t [ val]
- Select or set the cputime resource limit.
- -u [ val]
- Select or set the maxproc resource limit. The system-wide limit on the maximum number of processes allowed per UID can be viewed by examining the kern.maxprocperuid sysctl(8) variable. The maximum number of processes that can be running simultaneously in the entire system is limited to the value of the kern.maxproc sysctl(8) variable.
- -v [ val]
- Select or set the virtualmem resource limit. This limit encompasses the entire VM space for the user process and is inclusive of text, data, bss, stack, brk(2), sbrk(2) and mmap(2)'d space.
- -p [ val]
- Select or set the pseudoterminals resource limit.
- -w [ val]
- Select or set the swapuse resource limit.
Valid values for val in the above set of options consist of either the string “
unlimited” or “
unlimit” for an infinite (or kernel-defined maximum) limit, or a numeric value optionally followed by a suffix. Values which relate to size default to a value in bytes, or one of the following suffixes may be used as a multiplier:
- 512 byte blocks.
- kilobytes (1024 bytes).
- megabytes (1024*1024 bytes).
The cputime resource defaults to a number of seconds, but a multiplier may be used, and as with size values, multiple values separated by a valid suffix are added together:
- 365 day years.
- Cause limits to completely ignore the environment it inherits.
Force all resource settings to be displayed even if other specific resource settings have been specified. For example, if you wish to disable core dumps when starting up the Usenet News system, but wish to set all other resource settings as well that apply to the “
news” account, you might use:
eval `limits -U news -aBec 0`
As with the setrlimit(2) call, only the superuser may raise process “hard” resource limits. Non-root users may, however, lower them or change “soft” resource limits within to any value below the hard limit. When invoked to execute a program, the failure of limits to raise a hard limit is considered a fatal error.
EXIT STATUSThe limits utility exits with EXIT_FAILURE if usage is incorrect in any way; i.e., an invalid option, or set/display options are selected in the same invocation, -e is used when running a program, etc. When run in display or eval mode, limits exits with a status of EXIT_SUCCESS. When run in command mode and execution of the command succeeds, the exit status will be whatever the executed program returns.
SEE ALSOcsh(1), env(1), limit(1), sh(1), getrlimit(2), setrlimit(2), login_cap(3), login.conf(5), rctl(8), sysctl(8)
BUGSThe limits utility does not handle commands with equal (‘
=’) signs in their names, for obvious reasons.
When eval output is selected, the /proc file system must be installed and mounted for the shell to be correctly determined, and therefore output syntax correct for the running shell. The default output is valid for sh(1), so this means that any usage of limits in eval mode prior mounting /proc may only occur in standard bourne shell scripts.
The limits utility makes no effort to ensure that resource settings emitted or displayed are valid and settable by the current user. Only a superuser account may raise hard limits, and when doing so the FreeBSD kernel will silently lower limits to values less than specified if the values given are too high.
|January 23, 2012||FreeBSD|