1 .\" Copyright (C) 2014 Michael Kerrisk <mtk.manpages@gmail.com>
3 .\" %%%LICENSE_START(VERBATIM)
4 .\" Permission is granted to make and distribute verbatim copies of this
5 .\" manual provided the copyright notice and this permission notice are
6 .\" preserved on all copies.
8 .\" Permission is granted to copy and distribute modified versions of this
9 .\" manual under the conditions for verbatim copying, provided that the
10 .\" entire resulting derived work is distributed under the terms of a
11 .\" permission notice identical to this one.
13 .\" Since the Linux kernel and libraries are constantly changing, this
14 .\" manual page may be incorrect or out-of-date. The author(s) assume no
15 .\" responsibility for errors or omissions, or for damages resulting from
16 .\" the use of the information contained herein. The author(s) may not
17 .\" have taken the same level of care in the production of this manual,
18 .\" which is licensed free of charge, as they might when working
21 .\" Formatted or processed versions of this manual, if unaccompanied by
22 .\" the source, must acknowledge the copyright and authors of this work.
26 .TH SCHED_SETSCHEDULER 2 2021-03-22 "Linux" "Linux Programmer's Manual"
28 sched_setscheduler, sched_getscheduler \-
29 set and get scheduling policy/parameters
34 .BI "int sched_setscheduler(pid_t " pid ", int " policy ,
35 .BI " const struct sched_param *" param );
36 .BI "int sched_getscheduler(pid_t " pid );
40 .BR sched_setscheduler ()
42 sets both the scheduling policy and parameters for the
43 thread whose ID is specified in \fIpid\fP.
44 If \fIpid\fP equals zero, the
45 scheduling policy and parameters of the calling thread will be set.
47 The scheduling parameters are specified in the
49 argument, which is a pointer to a structure of the following form:
61 In the current implementation, the structure contains only one field,
65 depends on the selected policy.
67 Currently, Linux supports the following "normal"
68 (i.e., non-real-time) scheduling policies as values that may be specified in
72 the standard round-robin time-sharing policy;
73 .\" In the 2.6 kernel sources, SCHED_OTHER is actually called
77 for "batch" style execution of processes; and
82 low priority background jobs.
84 For each of the above policies,
85 .IR param\->sched_priority
88 Various "real-time" policies are also supported,
89 for special time-critical applications that need precise control over
90 the way in which runnable threads are selected for execution.
91 For the rules governing when a process may use these policies, see
93 The real-time policies that may be specified in
98 a first-in, first-out policy; and
101 a round-robin policy.
103 For each of the above policies,
104 .IR param\->sched_priority
105 specifies a scheduling priority for the thread.
106 This is a number in the range returned by calling
107 .BR sched_get_priority_min (2)
109 .BR sched_get_priority_max (2)
112 On Linux, these system calls return, respectively, 1 and 99.
114 Since Linux 2.6.32, the
115 .B SCHED_RESET_ON_FORK
119 .BR sched_setscheduler ().
120 As a result of including this flag, children created by
122 do not inherit privileged scheduling policies.
127 .BR sched_getscheduler ()
128 returns the current scheduling policy of the thread
129 identified by \fIpid\fP.
130 If \fIpid\fP equals zero, the policy of the
131 calling thread will be retrieved.
134 .BR sched_setscheduler ()
137 .BR sched_getscheduler ()
138 returns the policy for the thread (a nonnegative integer).
139 On error, both calls return \-1, and
141 is set to indicate the error.
152 .RB ( sched_setscheduler ())
154 is not one of the recognized policies.
157 .RB ( sched_setscheduler ())
159 does not make sense for the specified
163 The calling thread does not have appropriate privileges.
166 The thread whose ID is \fIpid\fP could not be found.
168 POSIX.1-2001, POSIX.1-2008 (but see BUGS below).
169 The \fBSCHED_BATCH\fP and \fBSCHED_IDLE\fP policies are Linux-specific.
171 Further details of the semantics of all of the above "normal"
172 and "real-time" scheduling policies can be found in the
175 That page also describes an additional policy,
177 which is settable only via
178 .BR sched_setattr (2).
180 POSIX systems on which
181 .BR sched_setscheduler ()
183 .BR sched_getscheduler ()
185 .B _POSIX_PRIORITY_SCHEDULING
188 POSIX.1 does not detail the permissions that an unprivileged
189 thread requires in order to call
190 .BR sched_setscheduler (),
191 and details vary across systems.
192 For example, the Solaris 7 manual page says that
193 the real or effective user ID of the caller must
194 match the real user ID or the save set-user-ID of the target.
196 The scheduling policy and parameters are in fact per-thread
198 The value returned from a call to
200 can be passed in the argument
204 as 0 will operate on the attributes of the calling thread,
205 and passing the value returned from a call to
207 will operate on the attributes of the main thread of the thread group.
208 (If you are using the POSIX threads API, then use
209 .BR pthread_setschedparam (3),
210 .BR pthread_getschedparam (3),
212 .BR pthread_setschedprio (3),
217 POSIX.1 says that on success,
218 .BR sched_setscheduler ()
219 should return the previous scheduling policy.
221 .BR sched_setscheduler ()
222 does not conform to this requirement,
223 since it always returns 0 on success.
229 .BR sched_get_priority_max (2),
230 .BR sched_get_priority_min (2),
231 .BR sched_getaffinity (2),
232 .BR sched_getattr (2),
233 .BR sched_getparam (2),
234 .BR sched_rr_get_interval (2),
235 .BR sched_setaffinity (2),
236 .BR sched_setattr (2),
237 .BR sched_setparam (2),
240 .BR capabilities (7),