ulimit - Man Page

set or report file size limit


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


ulimit [-f] [blocks]


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


The ulimit utility shall conform to the Base Definitions volume of POSIX.1-2017, Section 12.2, Utility Syntax Guidelines.

The following option shall be supported:


Set (or report, if no blocks operand is present), the file size limit in blocks. The -f option shall also be the default case.


The following operand shall be supported:


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


Not used.

Input Files


Environment Variables

The following environment variables shall affect the execution of ulimit:


Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of POSIX.1-2017, Section 8.2, Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)


If set to a non-empty string value, override the values of all the other internationalization variables.


Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments).


Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.


Determine the location of message catalogs for the processing of LC_MESSAGES.

Asynchronous Events



The standard output shall be used when no blocks operand is present. If the current number of blocks is limited, the number of blocks in the current limit shall be written in the following format:

"%d\n", <number of 512-byte blocks>

If there is no current limit on the number of blocks, in the POSIX locale the following format shall be used:



The standard error shall be used only for diagnostic messages.

Output Files


Extended Description


Exit Status

The following exit values shall be returned:


Successful completion.


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

Consequences of Errors


The following sections are informative.

Application Usage

Since ulimit affects the current shell execution environment, it is always provided as a shell regular built-in. If it is called in a separate utility execution environment, such as one of the following:

nohup ulimit -f 10000
env ulimit 10000

it does not affect the file size limit of the caller's environment.

Once a limit has been decreased by a process, it cannot be increased (unless appropriate privileges are involved), even back to the original system limit.


Set the file size limit to 51200 bytes:

ulimit -f 100



Future Directions


See Also

The Base Definitions volume of POSIX.1-2017, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines

The System Interfaces volume of POSIX.1-2017, ulimit()

Referenced By

prlimit(1), renice(1).

2017 IEEE/The Open Group POSIX Programmer's Manual