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man pages section 1: User Commands

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Updated: Wednesday, July 27, 2022



limit, ulimit, unlimit - set or get limitations on the system resources available to the current shell and its descendents


/usr/bin/ulimit [-f] [blocks]


ulimit [- [HS] [a | cdfnstv]]
ulimit [- [HS] [c | d | f | n | s | t | v]] limit


limit [-h] [resource [limit]]
unlimit [-h] [resource]


ulimit [-HSacdfnstv] [limit]


ulimit [-HSacdfmnpstv] [limit]


ulimit [-SHabcdefilmnpqrstuvxT] [limit]



The ulimit utility sets or reports the file-size writing limit imposed on files written by the shell and its child processes (files of any size can be read). Only a process with appropriate privileges can increase the limit.


The Bourne shell built-in function, ulimit, prints or sets hard or soft resource limits. These limits are described in getrlimit(2).

If limit is not present, ulimit prints the specified limits. Any number of limits can be printed at one time. The –a option prints all limits.

If limit is present, ulimit sets the specified limit to limit. The string unlimited requests that the current limit, if any, be removed. Any user can set a soft limit to any value less than or equal to the hard limit. Any user can lower a hard limit. Only a user with appropriate privileges can raise or remove a hard limit. See getrlimit(2).

The –H option specifies a hard limit. The –S option specifies a soft limit. If neither option is specified, ulimit sets both limits and prints the soft limit.

The following options specify the resource whose limits are to be printed or set. If no option is specified, the file size limit is printed or set.


Maximum core file size (in 512-byte blocks)


Maximum size of data segment or heap (in Kbytes)


Maximum file size (in 512-byte blocks)


Maximum file descriptor plus 1


Maximum size of stack segment (in Kbytes)


Maximum CPU time (in seconds)


Maximum size of virtual memory (in Kbytes)


The C-shell built-in function, limit, limits the consumption by the current process or any process it spawns, each not to exceed limit on the specified resource. The string unlimited requests that the current limit, if any, be removed. If limit is omitted, prints the current limit. If resource is omitted, displays all limits.


Use hard limits instead of the current limits. Hard limits impose a ceiling on the values of the current limits. Only the privileged user can raise the hard limits.

resource is one of:


Maximum CPU seconds per process.


Largest single file allowed. Limited to the size of the filesystem and capabilities of the filesystem. See df(8).


The maximum size of a process's heap in kilobytes.


Maximum stack size for the process. The default stack size is 213.


Maximum size of a core dump (file). This is limited to the size of the filesystem.


Maximum number of file descriptors. Run the sysdef(8) command to obtain the maximum possible limits for your system. The values reported by sysdef are in hexadecimal, but can be translated into decimal numbers using the bc(1) command.


Maximum size of virtual memory.

limit is a number, with an optional scaling factor, as follows:


Hours (for cputime).


n kilobytes. This is the default for all but cputime.


n megabytes or minutes (for cputime).


Minutes and seconds (for cputime).

unlimit removes a limitation on resource. If no resource is specified, then all resource limitations are removed. See the description of the limit command for the list of resource names.


Remove corresponding hard limits. Only the privileged user can do this.


The Korn shell built-in function, ulimit, sets or displays a resource limit. The available resources limits are listed below. Many systems do not contain one or more of these limits. The limit for a specified resource is set when limit is specified. The value of limit can be a number in the unit specified below with each resource, or the value unlimited. The string unlimited requests that the current limit, if any, be removed. The –H and –S flags specify whether the hard limit or the soft limit for the specified resource is set. A hard limit cannot be increased once it is set. A soft limit can be increased up to the value of the hard limit. If neither the –H or –S options is specified, the limit applies to both. The current resource limit is printed when limit is omitted. In this case, the soft limit is printed unless –H is specified. When more than one resource is specified, then the limit name and unit is printed before the value.


Lists all of the current resource limits.


The number of 512-byte blocks on the size of core dumps.


The number of K-bytes on the size of the data area.


The number of 512-byte blocks on files written by child processes (files of any size can be read).


The number of file descriptors plus 1.


The number of K-bytes on the size of the stack area.


The number of seconds (CPU time) to be used by each process.


The number of K-bytes for virtual memory.

If no option is specified, –f is assumed.

Per-Shell Memory Parameters

The heapsize, datasize, and stacksize parameters are not system tunables. The only controls for these are hard limits, set in a shell startup file, or system-wide soft limits, which, for the current version of the Solaris OS, is 2 13bytes.


ulimit sets or displays resource limits. These limits apply to the current process and to each child process created after the resource limit has been set. If limit is specified, the resource limit is set, otherwise, its current value is displayed on standard output.

Increasing the limit for a resource usually requires special privileges. Some systems allow you to lower resource limits and later increase them. These are called soft limits. Once a hard limit is set the resource cannot be increased.

Different systems allow you to specify different resources and some restrict how much you can raise the limit of the resource.

The value of limit depends on the unit of the resource listed for each resource. In addition, limit can be “unlimited” to indicate no limit for that resource.

If you do not specify –H or –S, –S is used for listing and both –S and –H are used for setting resources.

If you do not specify any resource, the default is –f.

The following options are available for ulimit in ksh:


Displays all current resource limits.


Specifies the socket buffer size in bytes.


Specifies the core file size in blocks.


Specifies the data size in kbytes.


Specifies the file size in blocks.


Displays or sets a hard limit.


Specifies the number of file locks.


Specifies the locked address space in Kbytes.


Specifies the address space limit in Kbytes.


Specifies the number of open files.


Specifies the pipe buffer size in bytes.


Specifies the resident set size in Kbytes


Displays or sets a soft limit.


Specifies the stack size in Kbytes.


Specifies the number of threads.


Specifies the CPU time in seconds.


Specifies the number of processes.


Specifies the process size in Kbytes.


The bash ulimit function uses different units for the core file (–c) and file size (–f) limits than other ulimit implementations. The bash shell uses block size 1024b while other implementations use 512b blocks. This has to be taken into account when you write a code which is to be executed by different shells, like /etc/profile. For more information about the documentation of bash built-in function ulimit, see the bash(1) man page.


The following option is supported by /usr/bin/ulimit:


Sets (or reports, if no blocks operand is present), the file size limit in blocks. The –f option is also the default case.


The following operand is supported by /usr/bin/ulimit:


The number of 512-byte blocks to use as the new file size limit.



Example 1 Limiting the Stack Size

The following example limits the stack size to 512 kilobytes:

example% ulimit -s 512
example% ulimit -a
time(seconds)         unlimited
file(blocks)            100
data(kbytes)            523256
stack(kbytes)           512
coredump(blocks)        200
nofiles(descriptors)    64
memory(kbytes)          unlimited


Example 2 Limiting the Number of File Descriptors

The following command limits the number of file descriptors to 12:

example$ ulimit -n 12
example$ ulimit -a
time(seconds)            unlimited
file(blocks)             41943
data(kbytes)             523256
stack(kbytes)            8192
coredump(blocks)         200
nofiles(descriptors)     12
vmemory(kbytes)          unlimited


Example 3 Limiting the Core Dump File Size

The following command limits the size of a core dump file size to 0 kilobytes:

example% limit coredumpsize 0
example% limit
cputime                 unlimited
filesize                unlimited
datasize                523256 kbytes
stacksize               8192 kbytes
coredumpsize            0 kbytes
descriptors             64
memorysize              unlimited
Example 4 Removing the limitation for core file size

The following command removes the above limitation for the core file size:

example% unlimit coredumpsize
example% limit
cputime                 unlimited
filesize                unlimited
datasize                523256 kbytes
stacksize               8192 kbytes
coredumpsize            unlimited
descriptors             64
memorysize              unlimited

Environment Variables

See environ(7) for descriptions of the following environment variables that affect the execution of ulimit: LANG, LC_ALL , LC_CTYPE, LC_MESSAGES, and NLSPATH.

Exit Status

The following exit values are returned by ulimit:


Successful completion.

> 0

A request for a higher limit was rejected or an error occurred.


See attributes(7) for descriptions of the following attributes:

/usr/bin/ulimit, csh, ksh88, sh

Interface Stability


Interface Stability

See Also

bash(1), bc(1), csh(1), ksh(1), ksh88(1), sh(1), getrlimit(2), attributes(7), environ(7), standards(7), df(8), su(8), swap(8), sysdef(8)


Be aware of possible unexpected consequences when using ulimit in conjunction with other Solaris resource-limiting features, such as prctl(1). See resource-controls(7).

With the use of the project resource controls described in resource-controls(7), you should use prctl(1) to get an accurate observation of the limits in effect at any given time.