355 lines
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355 lines
8.2 KiB
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of GETPRIORITY</TITLE>
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</HEAD><BODY>
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<H1>GETPRIORITY</H1>
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Section: Linux Programmer's Manual (2)<BR>Updated: 2017-09-15<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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getpriority, setpriority - get/set program scheduling priority
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<B>#include <<A HREF="file:///usr/include/sys/time.h">sys/time.h</A>></B>
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<BR>
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<B>#include <<A HREF="file:///usr/include/sys/resource.h">sys/resource.h</A>></B>
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<P>
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<B>int getpriority(int </B><I>which</I><B>, id_t </B><I>who</I><B>);</B>
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<BR>
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<B>int setpriority(int </B><I>which</I><B>, id_t </B><I>who</I><B>, int </B><I>prio</I><B>);</B>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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The scheduling priority of the process, process group, or user, as
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indicated by
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<I>which</I>
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and
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<I>who</I>
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is obtained with the
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<B>getpriority</B>()
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call and set with the
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<B>setpriority</B>()
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call.
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The process attribute dealt with by these system calls is
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the same attribute (also known as the "nice" value) that is dealt with by
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<B><A HREF="/cgi-bin/man/man2html?2+nice">nice</A></B>(2).
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<P>
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The value
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<I>which</I>
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is one of
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<B>PRIO_PROCESS</B>,
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<B>PRIO_PGRP</B>,
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or
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<B>PRIO_USER</B>,
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and
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<I>who</I>
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is interpreted relative to
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<I>which</I>
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(a process identifier for
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<B>PRIO_PROCESS</B>,
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process group
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identifier for
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<B>PRIO_PGRP</B>,
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and a user ID for
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<B>PRIO_USER</B>).
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A zero value for
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<I>who</I>
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denotes (respectively) the calling process, the process group of the
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calling process, or the real user ID of the calling process.
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<P>
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The
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<I>prio</I>
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argument is a value in the range -20 to 19 (but see NOTES below).
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with -20 being the highest priority and 19 being the lowest priority.
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Attempts to set a priority outside this range
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are silently clamped to the range.
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The default priority is 0;
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lower values give a process a higher scheduling priority.
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<P>
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The
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<B>getpriority</B>()
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call returns the highest priority (lowest numerical value)
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enjoyed by any of the specified processes.
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The
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<B>setpriority</B>()
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call sets the priorities of all of the specified processes
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to the specified value.
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<P>
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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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<B>RLIMIT_NICE</B>
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soft limit; see
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<B><A HREF="/cgi-bin/man/man2html?2+getrlimit">getrlimit</A></B>(2)
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for details.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success,
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<B>getpriority</B>()
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returns the calling thread's nice value, which may be a negative number.
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On error, it returns -1 and sets
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<I>errno</I>
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to indicate the cause of the error.
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Since a successful call to
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<B>getpriority</B>()
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can legitimately return the value -1, it is necessary
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to clear the external variable
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<I>errno</I>
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prior to the
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call, then check it afterward to determine
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if -1 is an error or a legitimate value.
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<P>
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<B>setpriority</B>()
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returns 0 on success.
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On error, it returns -1 and sets
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<I>errno</I>
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to indicate the cause of the error.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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<DL COMPACT>
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<DT id="1"><B>EINVAL</B>
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<DD>
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<I>which</I>
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was not one of
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<B>PRIO_PROCESS</B>,
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<B>PRIO_PGRP</B>,
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or
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<B>PRIO_USER</B>.
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<DT id="2"><B>ESRCH</B>
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<DD>
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No process was located using the
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<I>which</I>
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and
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<I>who</I>
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values specified.
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</DL>
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<P>
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In addition to the errors indicated above,
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<B>setpriority</B>()
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may fail if:
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<DL COMPACT>
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<DT id="3"><B>EACCES</B>
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<DD>
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The caller attempted to set a lower nice value
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(i.e., a higher process priority), but did not
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have the required privilege (on Linux: did not have the
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<B>CAP_SYS_NICE</B>
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capability).
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<DT id="4"><B>EPERM</B>
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<DD>
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A process was located, but its effective user ID did not match
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either the effective or the real user ID of the caller,
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and was not privileged (on Linux: did not have the
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<B>CAP_SYS_NICE</B>
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capability).
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But see NOTES below.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>CONFORMING TO</H2>
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POSIX.1-2001, POSIX.1-2008,
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SVr4, 4.4BSD (these interfaces first appeared in 4.2BSD).
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<A NAME="lbAH"> </A>
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<H2>NOTES</H2>
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For further details on the nice value, see
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<B><A HREF="/cgi-bin/man/man2html?7+sched">sched</A></B>(7).
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<P>
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<I>Note</I>:
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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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<B><A HREF="/cgi-bin/man/man2html?7+sched">sched</A></B>(7).
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<P>
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A child created by
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<B><A HREF="/cgi-bin/man/man2html?2+fork">fork</A></B>(2)
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inherits its parent's nice value.
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The nice value is preserved across
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<B><A HREF="/cgi-bin/man/man2html?2+execve">execve</A></B>(2).
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<P>
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The details on the condition for
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<B>EPERM</B>
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depend on the system.
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The above description is what POSIX.1-2001 says, and seems to be followed on
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all System V-like systems.
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Linux kernels before 2.6.12 required the real or
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effective user ID of the caller to match
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the real user of the process <I>who</I> (instead of its effective user ID).
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Linux 2.6.12 and later require
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the effective user ID of the caller to match
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the real or effective user ID of the process <I>who</I>.
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All BSD-like systems (SunOS 4.1.3, Ultrix 4.2,
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4.3BSD, FreeBSD 4.3, OpenBSD-2.5, ...) behave in the same
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manner as Linux 2.6.12 and later.
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<P>
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Including
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<I><<A HREF="file:///usr/include/sys/time.h">sys/time.h</A>></I>
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is not required these days, but increases portability.
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(Indeed,
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<I><<A HREF="file:///usr/include/sys/resource.h">sys/resource.h</A>></I>
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defines the
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<I>rusage</I>
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structure with fields of type
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<I>struct timeval</I>
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defined in
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<I><<A HREF="file:///usr/include/sys/time.h">sys/time.h</A>></I>.)
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<A NAME="lbAI"> </A>
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<H3>C library/kernel differences</H3>
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Within the kernel, nice values are actually represented
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using the range 40..1
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(since negative numbers are error codes) and these are the values
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employed by the
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<B>setpriority</B>()
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and
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<B>getpriority</B>()
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system calls.
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The glibc wrapper functions for these system calls handle the
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translations between the user-land and kernel representations
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of the nice value according to the formula
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<I>unice = 20 - knice</I>.
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(Thus, the kernel's 40..1 range corresponds to the
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range -20..19 as seen by user space.)
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<A NAME="lbAJ"> </A>
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<H2>BUGS</H2>
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According to POSIX, the nice value is a per-process setting.
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However, under the current Linux/NPTL implementation of POSIX threads,
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the nice value is a per-thread attribute:
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different threads in the same process can have different nice values.
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Portable applications should avoid relying on the Linux behavior,
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which may be made standards conformant in the future.
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<A NAME="lbAK"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?1+nice">nice</A></B>(1),
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<B><A HREF="/cgi-bin/man/man2html?1+renice">renice</A></B>(1),
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<B><A HREF="/cgi-bin/man/man2html?2+fork">fork</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?7+capabilities">capabilities</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?7+sched">sched</A></B>(7)
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<P>
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<I>Documentation/scheduler/sched-nice-design.txt</I>
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in the Linux kernel source tree (since Linux 2.6.23)
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<A NAME="lbAL"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="5"><A HREF="#lbAB">NAME</A><DD>
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<DT id="6"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="7"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="8"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="9"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="10"><A HREF="#lbAG">CONFORMING TO</A><DD>
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<DT id="11"><A HREF="#lbAH">NOTES</A><DD>
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<DL>
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<DT id="12"><A HREF="#lbAI">C library/kernel differences</A><DD>
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</DL>
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<DT id="13"><A HREF="#lbAJ">BUGS</A><DD>
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<DT id="14"><A HREF="#lbAK">SEE ALSO</A><DD>
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<DT id="15"><A HREF="#lbAL">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:32 GMT, March 31, 2021
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