man2/nice.2

   1 .\" Copyright (c) 1992 Drew Eckhardt <drew@cs.colorado.edu>, March 28, 1992
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  25 .\" Modified by Michael Haardt <michael@moria.de>
  26 .\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
  27 .\" Modified 1996-11-04 by Eric S. Raymond <esr@thyrsus.com>
  28 .\" Modified 2001-06-04 by aeb
  29 .\" Modified 2004-05-27 by Michael Kerrisk <mtk.manpages@gmail.com>
  30 .\"
  31 .TH NICE 2 2016-03-15 "Linux" "Linux Programmer's Manual"
  32 .SH NAME
  33 nice \- change process priority
  34 .SH SYNOPSIS
  35 .B #include <unistd.h>
  36 .sp
  37 .BI "int nice(int " inc );
  38 .sp
  39 .in -4n
  40 Feature Test Macro Requirements for glibc (see
  41 .BR feature_test_macros (7)):
  42 .in
  43 .sp
  44 .BR nice ():
  45 _XOPEN_SOURCE
  46     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  47     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  48 .SH DESCRIPTION
  49 .BR nice ()
  50 adds
  51 .I inc
  52 to the nice value for the calling thread.
  53 (A higher nice value means a low priority.)
  54 Only the super\%user may specify a negative increment,
  55 or priority increase.
  56
  57 The range of the nice value is +19 (low priority) to \-20 (high priority).
  58 Attempts to set a nice value outside the range are clamped to the range.
  59 .SH RETURN VALUE
  60 On success, the new nice value is returned (but see NOTES below).
  61 On error, \-1 is returned, and
  62 .I errno
  63 is set appropriately.
  64 .SH ERRORS
  65 .TP
  66 .B EPERM
  67 The calling process attempted to increase its priority by
  68 supplying a negative
  69 .I inc
  70 but has insufficient privileges.
  71 Under Linux, the
  72 .B CAP_SYS_NICE
  73 capability is required.
  74 (But see the discussion of the
  75 .B RLIMIT_NICE
  76 resource limit in
  77 .BR setrlimit (2).)
  78 .SH CONFORMING TO
  79 POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
  80 However, the Linux and (g)libc
  81 (earlier than glibc 2.2.4) return value is nonstandard, see below.
  82 SVr4 documents an additional
  83 .B EINVAL
  84 error code.
  85 .SH NOTES
  86 For further details on the nice value, see
  87 .BR sched (7).
  88
  89 .IR Note :
  90 the addition of the "autogroup" feature in Linux 2.6.38 means that
  91 the nice value no longer has its traditional effect in many circumstances.
  92 For details, see
  93 .BR sched (7).
  94
  95 SUSv2 and POSIX.1 specify that
  96 .BR nice ()
  97 should return the new nice value.
  98 However, the Linux system call and the
  99 .BR nice ()
 100 library function provided in older versions of (g)libc
 101 (earlier than glibc 2.2.4) return 0 on success.
 102 The new nice value can be found using
 103 .BR getpriority (2).
 104 .\"
 105 .SS C library/kernel differences
 106 Since glibc 2.2.4,
 107 .BR nice ()
 108 is implemented as a library function that calls
 109 .BR getpriority (2)
 110 to obtain the new nice value to be returned to the caller.
 111 With this implementation,
 112 a successful call can legitimately return \-1.
 113 To reliably detect an error, set
 114 .I errno
 115 to 0 before the call, and check its value when
 116 .BR nice ()
 117 returns \-1.
 118 .SH SEE ALSO
 119 .BR nice (1),
 120 .BR renice (1),
 121 .BR fork (2),
 122 .BR getpriority (2),
 123 .BR setpriority (2),
 124 .BR capabilities (7),
 125 .BR sched (7)