mirror of https://github.com/mkerrisk/man-pages
136 lines
4.1 KiB
Groff
136 lines
4.1 KiB
Groff
.\" Copyright (c) 1992 Drew Eckhardt <drew@cs.colorado.edu>, March 28, 1992
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.\" Modified by Michael Haardt <michael@moria.de>
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.\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
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.\" Modified 1996-11-04 by Eric S. Raymond <esr@thyrsus.com>
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.\" Modified 2001-06-04 by aeb
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.\" Modified 2004-05-27 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.TH NICE 2 2021-03-22 "Linux" "Linux Programmer's Manual"
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.SH NAME
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nice \- change process priority
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.SH SYNOPSIS
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.nf
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.B #include <unistd.h>
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.PP
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.BI "int nice(int " inc );
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.fi
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.PP
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.RS -4
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.RE
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.PP
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.BR nice ():
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.nf
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_XOPEN_SOURCE
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|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
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|| /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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.fi
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.SH DESCRIPTION
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.BR nice ()
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adds
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.I inc
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to the nice value for the calling thread.
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(A higher nice value means a lower priority.)
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.PP
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The range of the nice value is +19 (low priority) to \-20 (high priority).
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Attempts to set a nice value outside the range are clamped to the range.
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.PP
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Traditionally, only a privileged process could lower the nice value
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(i.e., set a higher priority).
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However, since Linux 2.6.12, an unprivileged process can decrease
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the nice value of a target process that has a suitable
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.BR RLIMIT_NICE
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soft limit; see
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.BR getrlimit (2)
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for details.
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.SH RETURN VALUE
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On success, the new nice value is returned (but see NOTES below).
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On error, \-1 is returned, and
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.I errno
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is set to indicate the error.
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.PP
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A successful call can legitimately return \-1.
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To detect an error, set
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.I errno
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to 0 before the call, and check whether it is nonzero after
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.BR nice ()
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returns \-1.
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.SH ERRORS
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.TP
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.B EPERM
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The calling process attempted to increase its priority by
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supplying a negative
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.I inc
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but has insufficient privileges.
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Under Linux, the
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.B CAP_SYS_NICE
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capability is required.
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(But see the discussion of the
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.B RLIMIT_NICE
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resource limit in
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.BR setrlimit (2).)
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.SH CONFORMING TO
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POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
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However, the raw system call and (g)libc
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(earlier than glibc 2.2.4) return value is nonstandard, see below.
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.\" SVr4 documents an additional
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.\" .B EINVAL
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.\" error code.
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.SH NOTES
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For further details on the nice value, see
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.BR sched (7).
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.PP
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.IR Note :
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the addition of the "autogroup" feature in Linux 2.6.38 means that
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the nice value no longer has its traditional effect in many circumstances.
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For details, see
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.BR sched (7).
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.\"
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.SS C library/kernel differences
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POSIX.1 specifies that
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.BR nice ()
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should return the new nice value.
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However, the raw Linux system call returns 0 on success.
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Likewise, the
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.BR nice ()
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wrapper function provided in glibc 2.2.3 and earlier returns 0 on success.
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.PP
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Since glibc 2.2.4, the
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.BR nice ()
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wrapper function provided by glibc provides conformance to POSIX.1 by calling
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.BR getpriority (2)
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to obtain the new nice value, which is then returned to the caller.
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.SH SEE ALSO
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.BR nice (1),
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.BR renice (1),
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.BR fork (2),
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.BR getpriority (2),
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.BR getrlimit (2),
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.BR setpriority (2),
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.BR capabilities (7),
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.BR sched (7)
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