The ulimit() function provides for control over process limits. It is effective in limiting the growth of regular files. Pipes are limited to PIPE_MAX bytes.

The cmd values, defined in <ulimit.h>, include:

UL_GETFSIZE

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.

UL_SETFSIZE

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 rlimit_t, the actual value set is unspecified.

UL_GMEMLIM

Get the maximum possible break value (see brk(2)).

UL_GDESLIM

Get the current value of the maximum number of open files per process configured in the system.

Upon successful completion, ulimit() returns the value of the requested limit. Otherwise, -1 is returned, the limit is not changed, and errno is set to indicate the error.

The ulimit() function will fail if:

EINVAL

The cmd argument is not valid.

EPERM

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

Since 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 if errno is non-zero.

The getrlimit() and setrlimit() functions provide a more general interface for controlling process limits, and are preferred over ulimit(). See getrlimit(2).

brk(2), getrlimit(2), write(2)