ulimit - Man Page

get and set process limits


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.


#include <ulimit.h>

long ulimit(int cmd, ...);


The ulimit() function shall control process limits. The process limits that can be controlled by this function include the maximum size of a single file that can be written (this is equivalent to using setrlimit() with RLIMIT_FSIZE). The cmd values, defined in <ulimit.h>, include:


Return the file size limit (RLIMIT_FSIZE) of the process. The limit shall be in units of 512-byte blocks and shall be inherited by child processes. Files of any size can be read. The return value shall be the integer part of the soft file size limit divided by 512. If the result cannot be represented as a long, the result is unspecified.


Set the file size limit for output operations of the process to the value of the second argument, taken as a long, multiplied by 512. If the result would overflow an rlim_t, the actual value set is unspecified. Any process may decrease its own limit, but only a process with appropriate privileges may increase the limit. The return value shall be the integer part of the new file size limit divided by 512.

The ulimit() function shall not change the setting of errno if successful.

As all return values are permissible in a successful situation, an application wishing to check for error situations should set errno to 0, then call ulimit(), and, if it returns -1, check to see if errno is non-zero.

Return Value

Upon successful completion, ulimit() shall return the value of the requested limit. Otherwise, -1 shall be returned and errno set to indicate the error.


The ulimit() function shall fail and the limit shall be unchanged if:


The cmd argument is not valid.


A process not having appropriate privileges attempts to increase its file size limit.

The following sections are informative.



Application Usage

Since the ulimit() function uses type long rather than rlim_t, this function is not sufficient for file sizes on many current systems. Applications should use the getrlimit() or setrlimit() functions instead of the obsolescent ulimit() function.



Future Directions

The ulimit() function may be removed in a future version.

See Also

exec, getrlimit(), write()

The Base Definitions volume of POSIX.1-2017, <ulimit.h>

Referenced By

exec(3p), fclose(3p), fflush(3p), fputc(3p), fputwc(3p), fseek(3p), getrlimit(3p), sh(1p), ulimit(1p), ulimit.h(0p), write(3p).

2017 IEEE/The Open Group POSIX Programmer's Manual