'\" et
.TH SCHED_SETSCHEDULER "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
sched_setscheduler
\(em set scheduling policy and parameters
(\fBREALTIME\fP)
.SH SYNOPSIS
.LP
.nf
#include <sched.h>
.P
int sched_setscheduler(pid_t \fIpid\fP, int \fIpolicy\fP,
    const struct sched_param *\fIparam\fP);
.fi
.SH DESCRIPTION
The
\fIsched_setscheduler\fR()
function shall set the scheduling policy and scheduling parameters
of the process specified by
.IR pid
to
.IR policy
and the parameters specified in the
.BR sched_param
structure pointed to by
.IR param ,
respectively. The value of the
.IR sched_priority
member in the
.BR sched_param
structure shall be any integer within the inclusive priority range
for the scheduling policy specified by
.IR policy .
If the value of
.IR pid
is negative, the behavior of the
\fIsched_setscheduler\fR()
function is unspecified.
.P
The possible values for the
.IR policy
parameter are defined in the
.IR <sched.h> 
header.
.P
If a process specified by
.IR pid
exists, and if the calling process has permission, the scheduling
policy and scheduling parameters shall be set for the process whose
process ID is equal to
.IR pid .
.P
If
.IR pid
is zero, the scheduling policy and scheduling parameters shall be
set for the calling process.
.P
The conditions under which one process has appropriate privileges to
change the scheduling parameters of another process are
implementation-defined.
.P
Implementations may require that the requesting process have permission
to set its own scheduling parameters or those of another process.
Additionally, implementation-defined restrictions may apply as to the
appropriate privileges required to set the scheduling
policy of the process, or the scheduling policy of another process,
to a particular value.
.P
The
\fIsched_setscheduler\fR()
function shall be considered successful if it succeeds in setting the
scheduling policy and scheduling parameters of the process specified by
.IR pid
to the values specified by
.IR policy
and the structure pointed to by
.IR param ,
respectively.
.P
See
.IR "Scheduling Policies"
for a description on how this function affects the scheduling of the
threads within the target process.
.P
If the current scheduling policy for the target process is not
SCHED_FIFO, SCHED_RR,
or SCHED_SPORADIC,
the result is implementation-defined; this case includes the
SCHED_OTHER policy.
.P
The specified
.IR sched_ss_repl_period
shall be greater than or equal to the specified
.IR sched_ss_init_budget
for the function to succeed; if it is not, then the function shall
fail.
.P
The value of
.IR sched_ss_max_repl
shall be within the inclusive range [1,{SS_REPL_MAX}] for the function
to succeed; if not, the function shall fail. It is unspecified whether the
.IR sched_ss_repl_period
and
.IR sched_ss_init_budget
values are stored as provided by this function or are rounded to
align with the resolution of the clock being used.
.P
This function is not atomic with respect to other threads in the
process. Threads may continue to execute while this function call is in
the process of changing the scheduling policy and associated scheduling
parameters for the underlying kernel-scheduled entities used by the
process contention scope threads.
.SH "RETURN VALUE"
Upon successful completion, the function shall return the former
scheduling policy of the specified process. If the
\fIsched_setscheduler\fR()
function fails to complete successfully, the policy and scheduling
parameters shall remain unchanged, and the function shall return a
value of \-1 and set
.IR errno
to indicate the error.
.SH ERRORS
The
\fIsched_setscheduler\fR()
function shall fail if:
.TP
.BR EINVAL
The value of the
.IR policy
parameter is invalid, or one or more of the parameters contained in
.IR param
is outside the valid range for the specified scheduling policy.
.TP
.BR EPERM
The requesting process does not have permission to set either or both
of the scheduling parameters or the scheduling policy of the specified
process.
.TP
.BR ESRCH
No process can be found corresponding to that specified by
.IR pid .
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
None.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "Scheduling Policies",
.IR "\fIsched_getparam\fR\^(\|)",
.IR "\fIsched_getscheduler\fR\^(\|)",
.IR "\fIsched_setparam\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<sched.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .