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32 .\" @(#)getpriority.2 6.9 (Berkeley) 3/10/91
34 .\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
35 .\" Modified 1996-07-01 by Andries Brouwer <aeb@cwi.nl>
36 .\" Modified 1996-11-06 by Eric S. Raymond <esr@thyrsus.com>
37 .\" Modified 2001-10-21 by Michael Kerrisk <mtk.manpages@gmail.com>
38 .\" Corrected statement under EPERM to clarify privileges required
39 .\" Modified 2002-06-21 by Michael Kerrisk <mtk.manpages@gmail.com>
40 .\" Clarified meaning of 0 value for 'who' argument
41 .\" Modified 2004-05-27 by Michael Kerrisk <mtk.manpages@gmail.com>
43 .\" FIXME Oct 2008: Denys Vlasenko is working on a PRIO_THREAD feature that
44 .\" is likely to get included in mainline; this will need to be documented.
46 .TH GETPRIORITY 2 2008-05-29 "Linux" "Linux Programmer's Manual"
48 getpriority, setpriority \- get/set program scheduling priority
50 .B #include <sys/time.h>
52 .B #include <sys/resource.h>
54 .BI "int getpriority(int " which ", int " who );
56 .BI "int setpriority(int " which ", int " who ", int " prio );
58 The scheduling priority of the process, process group, or user, as
78 is interpreted relative to
80 (a process identifier for
89 denotes (respectively) the calling process, the process group of the
90 calling process, or the real user ID of the calling process.
92 is a value in the range \-20 to 19 (but see the Notes below).
93 The default priority is 0;
94 lower priorities cause more favorable scheduling.
98 call returns the highest priority (lowest numerical value)
99 enjoyed by any of the specified processes.
102 call sets the priorities of all of the specified processes
103 to the specified value.
104 Only the superuser may lower priorities.
108 can legitimately return the value \-1, it is necessary
109 to clear the external variable
112 call, then check it afterward to determine
113 if \-1 is an error or a legitimate value.
116 call returns 0 if there is no error, or
129 No process was located using the
135 In addition to the errors indicated above,
140 The caller attempted to lower a process priority, but did not
141 have the required privilege (on Linux: did not have the
144 Since Linux 2.6.12, this error only occurs if the caller attempts
145 to set a process priority outside the range of the
147 soft resource limit of the target process; see
152 A process was located, but its effective user ID did not match
153 either the effective or the real user ID of the caller,
154 and was not privileged (on Linux: did not have the
159 SVr4, 4.4BSD (these function calls first appeared in 4.2BSD),
164 inherits its parent's nice value.
165 The nice value is preserved across
168 The degree to which their relative nice value affects the scheduling of
169 processes varies across UNIX systems, and,
170 on Linux, across kernel versions.
171 Starting with kernel 2.6.23, Linux adopted an algorithm that causes
172 relative differences in nice values to have a much stronger effect.
173 This causes very low nice values (+19) to truly provide little CPU
174 to a process whenever there is any other
175 higher priority load on the system,
176 and makes high nice values (\-20) deliver most of the CPU to applications
177 that require it (e.g., some audio applications).
179 The details on the condition for
181 depend on the system.
182 The above description is what POSIX.1-2001 says, and seems to be followed on
183 all System V-like systems.
184 Linux kernels before 2.6.12 required the real or
185 effective user ID of the caller to match
186 the real user of the process \fIwho\fP (instead of its effective user ID).
187 Linux 2.6.12 and later require
188 the effective user ID of the caller to match
189 the real or effective user ID of the process \fIwho\fP.
190 All BSD-like systems (SunOS 4.1.3, Ultrix 4.2,
191 4.3BSD, FreeBSD 4.3, OpenBSD-2.5, ...) behave in the same
192 manner as Linux 2.6.12 and later.
194 The actual priority range varies between kernel versions.
195 Linux before 1.3.36 had \-infinity..15.
196 Since kernel 1.3.43 Linux has the range \-20..19.
197 Within the kernel, nice values are actually represented
198 using the corresponding range 40..1
199 (since negative numbers are error codes) and these are the values
205 The glibc wrapper functions for these system calls handle the
206 translations between the user-land and kernel representations
207 of the nice value according to the formula
208 .IR "unice\ =\ 20\ \-\ knice" .
210 On some systems, the range of nice values is \-20..20.
214 is not required these days, but increases portability.
219 structure with fields of type
229 .I Documentation/scheduler/sched-nice-design.txt
230 in the kernel source tree (since Linux 2.6.23).