The Single UNIX ® Specification, Version 2
Copyright © 1997 The Open Group


ulimit - get and set process limits


#include <ulimit.h>

long int ulimit(int cmd, ...);


The ulimit() function provides for control over process limits. The cmd values, defined in <ulimit.h> include:
Return the soft file size limit of the process. The limit is in units of 512-byte blocks and is inherited by child processes. Files of any size can be read. The return value is the integer part of the soft file size limit divided by 512. If the result cannot be represented as a long int, the result is unspecified.
Set the hard and soft file size limits for output operations of the process to the value of the second argument, taken as a long int. Any process may decrease its own hard limit, but only a process with appropriate privileges may increase the limit. The new file size limit is returned. The hard and soft file size limits are set to the specified value multiplied by 512. If the result would overflow an rlim_t, the actual value set is unspecified.

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


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


The ulimit() function will fail and the limit will be unchanged if:
The cmd argument is not valid.
A process not having appropriate privileges attempts to increase its file size limit.




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.




getrlimit(), setrlimit(), write(), <ulimit.h>.


Derived from Issue 1 of the SVID.

UNIX ® is a registered Trademark of The Open Group.
Copyright © 1997 The Open Group
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