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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | STANDARDS | HISTORY | NOTES | BUGS | SEE ALSO | COLOPHON |
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sched_setscheduler(2) System Calls Manual sched_setscheduler(2)
sched_setscheduler, sched_getscheduler - set and get scheduling
policy/parameters
Standard C library (libc, -lc)
#include <sched.h>
int sched_setscheduler(pid_t pid, int policy,
const struct sched_param *param);
int sched_getscheduler(pid_t pid);
The sched_setscheduler() system call sets both the scheduling
policy and parameters for the thread whose ID is specified in pid.
If pid equals zero, the scheduling policy and parameters of the
calling thread will be set.
The scheduling parameters are specified in the param argument,
which is a pointer to a structure of the following form:
struct sched_param {
...
int sched_priority;
...
};
In the current implementation, the structure contains only one
field, sched_priority. The interpretation of param depends on the
selected policy.
Currently, Linux supports the following "normal" (i.e., non-real-
time) scheduling policies as values that may be specified in
policy:
SCHED_OTHER
the standard round-robin time-sharing policy;
SCHED_BATCH
for "batch" style execution of processes; and
SCHED_IDLE
for running very low priority background jobs.
For each of the above policies, param->sched_priority must be 0.
Various "real-time" policies are also supported, for special time-
critical applications that need precise control over the way in
which runnable threads are selected for execution. For the rules
governing when a process may use these policies, see sched(7).
The real-time policies that may be specified in policy are:
SCHED_FIFO
a first-in, first-out policy; and
SCHED_RR
a round-robin policy.
For each of the above policies, param->sched_priority specifies a
scheduling priority for the thread. This is a number in the range
returned by calling sched_get_priority_min(2) and
sched_get_priority_max(2) with the specified policy. On Linux,
these system calls return, respectively, 1 and 99.
Since Linux 2.6.32, the SCHED_RESET_ON_FORK flag can be ORed in
policy when calling sched_setscheduler(). As a result of
including this flag, children created by fork(2) do not inherit
privileged scheduling policies. See sched(7) for details.
sched_getscheduler() returns the current scheduling policy of the
thread identified by pid. If pid equals zero, the policy of the
calling thread will be retrieved.
On success, sched_setscheduler() returns zero. On success,
sched_getscheduler() returns the policy for the thread (a
nonnegative integer). On error, both calls return -1, and errno
is set to indicate the error.
EINVAL Invalid arguments: pid is negative or param is NULL.
EINVAL (sched_setscheduler()) policy is not one of the recognized
policies.
EINVAL (sched_setscheduler()) param does not make sense for the
specified policy.
EPERM The calling thread does not have appropriate privileges.
ESRCH The thread whose ID is pid could not be found.
POSIX.1 does not detail the permissions that an unprivileged
thread requires in order to call sched_setscheduler(), and details
vary across systems. For example, the Solaris 7 manual page says
that the real or effective user ID of the caller must match the
real user ID or the save set-user-ID of the target.
The scheduling policy and parameters are in fact per-thread
attributes on Linux. The value returned from a call to gettid(2)
can be passed in the argument pid. Specifying pid as 0 will
operate on the attributes of the calling thread, and passing the
value returned from a call to getpid(2) will operate on the
attributes of the main thread of the thread group. (If you are
using the POSIX threads API, then use pthread_setschedparam(3),
pthread_getschedparam(3), and pthread_setschedprio(3), instead of
the sched_*(2) system calls.)
POSIX.1-2008 (but see BUGS below).
SCHED_BATCH and SCHED_IDLE are Linux-specific.
POSIX.1-2001.
Further details of the semantics of all of the above "normal" and
"real-time" scheduling policies can be found in the sched(7)
manual page. That page also describes an additional policy,
SCHED_DEADLINE, which is settable only via sched_setattr(2).
POSIX systems on which sched_setscheduler() and
sched_getscheduler() are available define
_POSIX_PRIORITY_SCHEDULING in <unistd.h>.
POSIX.1 says that on success, sched_setscheduler() should return
the previous scheduling policy. Linux sched_setscheduler() does
not conform to this requirement, since it always returns 0 on
success.
chrt(1), nice(2), sched_get_priority_max(2),
sched_get_priority_min(2), sched_getaffinity(2), sched_getattr(2),
sched_getparam(2), sched_rr_get_interval(2), sched_setaffinity(2),
sched_setattr(2), sched_setparam(2), sched_yield(2),
setpriority(2), capabilities(7), cpuset(7), sched(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.10.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-02-02. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.10 2024-07-23 sched_setscheduler(2)
Pages that refer to this page: chrt(1), uclampset(1), getrlimit(2), gettid(2), mlock(2), nanosleep(2), PR_SET_TIMERSLACK(2const), sched_get_priority_max(2), sched_setaffinity(2), sched_setattr(2), sched_setparam(2), syscalls(2), id_t(3type), posix_spawn(3), proc_pid_stat(5), systemd.exec(5), capabilities(7), cpuset(7), credentials(7), sched(7)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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