NAME

       nice - change process priority

SYNOPSIS

       #include <unistd.h>

       int nice(int inc);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       nice(): _XOPEN_SOURCE
           || /* Since glibc 2.19: */ _DEFAULT_SOURCE
           || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

       nice()  adds  inc  to the nice value for the calling thread.  (A higher nice value means a
       low priority.)

       The range of the nice value is +19 (low priority) to -20 (high priority).  Attempts to set
       a nice value outside the range are clamped to the range.

       Traditionally,  only  a  privileged process could lower the nice value (i.e., set a higher
       priority).  However, since Linux 2.6.12, an unprivileged process  can  decrease  the  nice
       value of a target process that has a suitable RLIMIT_NICE soft limit; see getrlimit(2) for
       details.

RETURN VALUE

       On success, the new nice value is returned  (but  see  NOTES  below).   On  error,  -1  is
       returned, and errno is set appropriately.

       A  successful  call can legitimately return -1.  To detect an error, set errno to 0 before
       the call, and check whether it is nonzero after nice() returns -1.

ERRORS

       EPERM  The calling process attempted to increase its priority by supplying a negative  inc
              but  has  insufficient  privileges.   Under  Linux,  the CAP_SYS_NICE capability is
              required.   (But  see  the  discussion  of  the  RLIMIT_NICE  resource   limit   in
              setrlimit(2).)

CONFORMING TO

       POSIX.1-2001,  POSIX.1-2008,  SVr4,  4.3BSD.   However,  the  raw  system call and (g)libc
       (earlier than glibc 2.2.4) return value is nonstandard, see below.

NOTES

       For further details on the nice value, see sched(7).

       Note: the addition of the "autogroup" feature in Linux 2.6.38 means that the nice value no
       longer has its traditional effect in many circumstances.  For details, see sched(7).

   C library/kernel differences
       POSIX.1  specifies  that  nice() should return the new nice value.  However, the raw Linux
       system call returns 0 on success.  Likewise, the nice() wrapper function provided in glibc
       2.2.3 and earlier returns 0 on success.

       Since  glibc  2.2.4, the nice() wrapper function provided by glibc provides conformance to
       POSIX.1 by calling getpriority(2) to obtain the new nice value, which is then returned  to
       the caller.

SEE ALSO

       nice(1),     renice(1),    fork(2),    getpriority(2),    getrlimit(2),    setpriority(2),
       capabilities(7), sched(7)

COLOPHON

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