NAME

getrlimit, setrlimit — control maximum system resource consumption

SYNOPSIS

#include <sys/resource.h>

int
getrlimit(int resource, struct rlimit *rlp);

int
setrlimit(int resource, const struct rlimit *rlp);

DESCRIPTION

Limits on the consumption of system resources by the current process and each process it creates may be obtained with the getrlimit() call, and set with the setrlimit() call.

The resource parameter is one of the following:

RLIMIT_CORE: The largest size (in bytes) core file that may be created.
RLIMIT_CPU: The maximum amount of CPU time (in seconds) to be used by each process.
RLIMIT_DATA: The maximum size (in bytes) of the data segment for a process; this includes memory allocated via malloc(3) and all other anonymous memory mapped via mmap(2).
RLIMIT_FSIZE: The largest size (in bytes) file that may be created.
RLIMIT_MEMLOCK: The maximum size (in bytes) which a process may lock into memory using the mlock(2) function.
RLIMIT_NOFILE: The maximum number of open files for this process.
RLIMIT_NPROC: The maximum number of simultaneous processes for this user id.
RLIMIT_RSS: The maximum size (in bytes) to which a process's resident set size may grow. This setting is no longer enforced, but retained for compatibility.
RLIMIT_STACK: The maximum size (in bytes) of the stack segment for a process, which defines how far a process's stack segment may be extended. Stack extension is performed automatically by the system, and is only used by the main thread of a process.

A resource limit is specified as a soft limit and a hard limit. When a soft limit is exceeded a process may receive a signal (for example, if the CPU time or file size is exceeded), but it will be allowed to continue execution until it reaches the hard limit (or modifies its resource limit). The rlimit structure is used to specify the hard and soft limits on a resource,

struct rlimit {
	rlim_t	rlim_cur;	/* current (soft) limit */
	rlim_t	rlim_max;	/* hard limit */
};

Only the superuser may raise the maximum limits. Other users may only alter rlim_cur within the range from 0 to rlim_max or (irreversibly) lower rlim_max.

An “infinite” value for a limit is defined as RLIM_INFINITY.

A value of RLIM_SAVED_CUR or RLIM_SAVED_MAX will be stored in rlim_cur or rlim_max respectively by getrlimit() if the value for the current or maximum resource limit cannot be stored in an rlim_t. The values RLIM_SAVED_CUR and RLIM_SAVED_MAX should not be used in a call to setrlimit() unless they were returned by a previous call to getrlimit().

Because this information is stored in the per-process information, this system call must be executed directly by the shell if it is to affect all future processes created by the shell; limit is thus a built-in command to csh(1) and ulimit is the sh(1) equivalent.

The system refuses to extend the data or stack space when the limits would be exceeded in the normal way: a brk(2) call fails if the data space limit is reached. When the stack limit is reached, the process receives a segmentation fault (SIGSEGV); if this signal is not caught by a handler using the signal stack, this signal will kill the process.

A file I/O operation that would create a file larger than the process' soft limit will cause the write to fail and a signal SIGXFSZ to be generated; this normally terminates the process, but may be caught. When the soft CPU time limit is exceeded, a signal SIGXCPU is sent to the offending process.

RETURN VALUES

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

ERRORS

getrlimit() and setrlimit() will fail if:

[EFAULT]: The address specified for rlp is invalid.
[EINVAL]: An unrecognized value for resource was specified.

In addition, setrlimit() may return the following errors:

[EINVAL]: The new rlim_cur is greater than the new rlim_max.
[EPERM]: The new rlim_max is greater than the current maximum limit value, and the caller is not the superuser.