nice(2)

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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   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at
   https://www.kernel.org/doc/man-pages/.

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