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NAME    [Toc]    [Back]

     getrlimit, setrlimit - control maximum system resource consumption

LIBRARY    [Toc]    [Back]

     Standard C Library (libc, -lc)

SYNOPSIS    [Toc]    [Back]

     #include <sys/resource.h>

     getrlimit(int resource, struct rlimit *rlp);

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

DESCRIPTION    [Toc]    [Back]

     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.  Resources of an arbitrary process can be
     obtained/changed using sysctl(3).

     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 defines how far a program may extend its
                     break with the sbrk(2) system call.

     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 imposes a limit on the amount of
                     physical memory to be given to a process; if memory is
                     tight, the system will prefer to take memory from processes
 that are exceeding their declared resident set

     RLIMIT_STACK    The maximum size (in bytes) of the stack segment for a
                     process; this defines how far a program's stack segment
                     may be extended.  Stack extension is performed automatically
 by the system.

     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 super-user 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.

     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.  Thus, shells provide built-in
     commands to change the limits (limit for csh(1), or ulimit for sh(1)).

     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 that 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

RETURN VALUES    [Toc]    [Back]

     A 0 return value indicates that the call succeeded, changing or returning
     the resource limit.  Otherwise, -1 is returned and the global variable
     errno is set to indicate the error.

ERRORS    [Toc]    [Back]

     The getrlimit() and setrlimit() will fail if:

     [EFAULT]           The address specified for rlp is invalid.

     [EINVAL]           Specified resource was invalid.

     [EINVAL]           In the setrlimit() call, the specified rlim_cur
                        exceeds the specified rlim_max.

     [EPERM]            The limit specified to setrlimit() would have raised
                        the maximum limit value, and the caller is not the

     The setrlimit() function may fail if:

     [EINVAL]           The limit specified to setrlimit() cannot be lowered,
                        because current usage is already higher than the

SEE ALSO    [Toc]    [Back]

     csh(1), sh(1), quotactl(2), sigaction(2), sigaltstack(2), sysctl(3)

HISTORY    [Toc]    [Back]

     The getrlimit() function call appeared in 4.2BSD.

BSD                            November 23, 2001                           BSD
[ Back ]
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