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-.TH SCHED_SETSCHEDULER 2 2014-10-02 "Linux" "Linux Programmer's Manual"
-.SH NAME
-sched_setscheduler, sched_getscheduler \-
-set and get scheduling policy/parameters
-.SH SYNOPSIS
-.nf
-.B #include <sched.h>
-.sp
-.BI "int sched_setscheduler(pid_t " pid ", int " policy ,
-.br
-.BI " const struct sched_param *" param );
-.sp
-.BI "int sched_getscheduler(pid_t " pid );
-.sp
-.fi
-.SH DESCRIPTION
-The
-.BR sched_setscheduler ()
-system call
-sets both the scheduling policy and parameters for the
-thread whose ID is specified in \fIpid\fP.
-If \fIpid\fP equals zero, the
-scheduling policy and parameters of the calling thread will be set.
-
-The scheduling parameters are specified in the
-.I param
-argument, which is a pointer to a structure of the following form:
-
-.nf
-.in +4n
-struct sched_param {
- ...
- int sched_priority;
- ...
-};
-.in
-.fi
-
-In the current implementation, the structure contains only one field,
-.IR sched_priority .
-The interpretation of
-.I 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
-.IR policy :
-.TP 14
-.BR SCHED_OTHER
-the standard round-robin time-sharing policy;
-.\" In the 2.6 kernel sources, SCHED_OTHER is actually called
-.\" SCHED_NORMAL.
-.TP
-.BR SCHED_BATCH
-for "batch" style execution of processes; and
-.TP
-.BR SCHED_IDLE
-for running
-.I very
-low priority background jobs.
-.PP
-For each of the above policies,
-.IR 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
-.BR sched (7).
-The real-time policies that may be specified in
-.IR policy
-are:
-.TP 14
-.BR SCHED_FIFO
-a first-in, first-out policy; and
-.TP
-.BR SCHED_RR
-a round-robin policy.
-.PP
-For each of the above policies,
-.IR param\->sched_priority
-specifies a scheduling priority for the thread.
-This is a number in the range returned by calling
-.BR sched_get_priority_min (2)
-and
-.BR sched_get_priority_max (2)
-with the specified
-.IR policy .
-On Linux, these system calls return, respectively, 1 and 99.
-
-Since Linux 2.6.32, the
-.B SCHED_RESET_ON_FORK
-flag can be ORed in
-.I policy
-when calling
-.BR sched_setscheduler ().
-As a result of including this flag, children created by
-.BR fork (2)
-do not inherit privileged scheduling policies.
-See
-.BR sched (7)
-for details.
-
-.BR sched_getscheduler ()
-returns the current scheduling policy of the thread
-identified by \fIpid\fP.
-If \fIpid\fP equals zero, the policy of the
-calling thread will be retrieved.
-.SH RETURN VALUE
-On success,
-.BR sched_setscheduler ()
-returns zero.
-On success,
-.BR sched_getscheduler ()
-returns the policy for the thread (a nonnegative integer).
-On error, both calls return \-1, and
-.I errno
-is set appropriately.
-.SH ERRORS
-.TP
-.B EINVAL
-Invalid arguments:
-.I pid
-is negative or
-.I param
-is NULL.
-.TP
-.B EINVAL
-.RB ( sched_setscheduler ())
-.I policy
-is not one of the recognized policies.
-.TP
-.B EINVAL
-.RB ( sched_setscheduler ())
-.I param
-does not make sense for the specified
-.IR policy .
-.TP
-.B EPERM
-The calling thread does not have appropriate privileges.
-.TP
-.B ESRCH
-The thread whose ID is \fIpid\fP could not be found.
-.SH CONFORMING TO
-POSIX.1-2001 (but see BUGS below).
-The \fBSCHED_BATCH\fP and \fBSCHED_IDLE\fP policies are Linux-specific.
-.SH NOTES
-Further details of the semantics of all of the above "normal"
-and "real-time" scheduling policies can be found in
-.BR sched (7).
-
-POSIX systems on which
-.BR sched_setscheduler ()
-and
-.BR sched_getscheduler ()
-are available define
-.B _POSIX_PRIORITY_SCHEDULING
-in \fI<unistd.h>\fP.
-
-POSIX.1 does not detail the permissions that an unprivileged
-thread requires in order to call
-.BR 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.
-.PP
-The scheduling policy and parameters are in fact per-thread
-attributes on Linux.
-The value returned from a call to
-.BR gettid (2)
-can be passed in the argument
-.IR pid .
-Specifying
-.I pid
-as 0 will operate on the attributes of the calling thread,
-and passing the value returned from a call to
-.BR 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
-.BR pthread_setschedparam (3),
-.BR pthread_getschedparam (3),
-and
-.BR pthread_setschedprio (3),
-instead of the
-.BR sched_* (2)
-system calls.)
-.SH BUGS
-POSIX says that on success,
-.BR sched_setscheduler ()
-should return the previous scheduling policy.
-Linux
-.BR sched_setscheduler ()
-does not conform to this requirement,
-since it always returns 0 on success.
-.SH SEE ALSO
-.ad l
-.nh
-.BR chrt (1),
-.BR nice (2),
-.BR sched_get_priority_max (2),
-.BR sched_get_priority_min (2),
-.BR sched_getaffinity (2),
-.BR sched_getattr (2),
-.BR sched_getparam (2),
-.BR sched_rr_get_interval (2),
-.BR sched_setaffinity (2),
-.BR sched_setattr (2),
-.BR sched_setparam (2),
-.BR sched_yield (2),
-.BR setpriority (2),
-.BR capabilities (7),
-.BR cpuset (7),
-.BR sched (7)
-.ad
-.SH COLOPHON
-This page is part of release 3.79 of the Linux
-.I man-pages
-project.
-A description of the project,
-information about reporting bugs,
-and the latest version of this page,
-can be found at
-\%http://www.kernel.org/doc/man\-pages/.
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