LIMITS(1) BSD General Commands Manual LIMITS(1)NAMElimits — set or display process resource limitsSYNOPSISlimits [-C class] [-SHB] [-ea] [-cdfklmnstuv [val]]
limits [-C class] [-SHB] [-cdfklmnstuv [val]] [-E] [name=value ...]
[command]
limits [-U user] [-SHB] [-ea] [-cdflmnstuv [val]]
limits [-U user] [-SHB] [-cdflmnstuv [val]] [-E] [name=value ...]
[command]
DESCRIPTION
The 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 command 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 flags, 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 filesystem for the parent process. If the shell is known
(i.e. it is one of sh, csh, bash, tcsh, ksh, pdksh or rc), limits
emits 'limit' or '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 which "user" belongs to. If
the user does not belong to a class, then the resource capa‐
bilities for the "default" class are used, if it exists, or
the "root" class if the user is a superuser account.
-S 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 flags.
-H 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 flags.
-B Select display or setting of both "soft" (current) or "hard"
(maximum) resource limits. If specific limits settings fol‐
low this switch, both soft and hard limits are affected until
overridden later with either the -S or -H flags. -e 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 [limit] Selects or sets the sbsize resource limit.
-c [limit] Select or set (if 'limit' is specified) the coredumpsize
resource limit. A value of 0 disables core dumps.
-d [limit] Select or set (if 'limit' is specified) the datasize resource
limit.
-f [limit] Select or set the filesize resource limit.
-k [limit] Select or set the posixlocks resource limit.
-l [limit] Select or set the memorylocked resource limit.
-m [limit] Select or set the memoryuse size limit.
-n [limit] Select or set the openfiles resource limit. The system-wide
limit on the maximum number of open files per process can be
viewed using the 'sysctl kern.maxfilesperproc' command. The
total number of simultaneously open files in the entire sys‐
tem is limited to the value displayed by the 'sysctl
kern.maxfiles' command.
-s [limit] Select or set the stacksize resource limit.
-t [limit] Select or set the cputime resource limit.
-u [limit] Select or set the maxproc resource limit. The system-wide
limit on the maximum number of processes allowed per UID can
be viewed using the 'sysctl kern.maxprocperuid' command. The
maximum number of processes that can be running simultane‐
ously in the entire system is limited to the value given by
the 'sysctl kern.maxproc' command.
-v [limit] 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.
Valid values for val in the above set of options consist of either the
string “infinity”, “inf”, “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:
b 512 byte blocks.
k kilobytes (1024 bytes).
m megabytes (1024*1024 bytes).
g gigabytes.
t terabytes.
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:
s seconds.
m minutes.
h hours.
d days.
w weeks.
y 365 day years.
-E Cause limits to completely ignore the environment it inherits.
-a Force all resource settings to be displayed even if other spe‐
cific 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.
DIAGNOSTICS
The 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 sta‐
tus will be whatever the executed program returns.
SEE ALSObuiltin(1), csh(1), env(1), limit(1), sh(1), getrlimit(2), setrlimit(2),
login_cap(3), login.conf(5), sysctl(8)BUGS
The limits utility does not handle commands with equal (``='') signs in
their names, for obvious reasons.
When eval output is selected, the /proc filesystem 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 emit‐
ted or displayed are valid and settable by the current user. Only a
superuser account may raise hard limits, and when doing so the DragonFly
kernel will silently lower limits to values less than specified if the
values given are too high.
BSD January 15, 1996 BSD
