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.TH GETPRIORITY "3P" 2013 "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
getpriority,
setpriority
\(em get and set the nice value
.SH SYNOPSIS
.LP
.nf
#include <sys/resource.h>
.P
int getpriority(int \fIwhich\fP, id_t \fIwho\fP);
int setpriority(int \fIwhich\fP, id_t \fIwho\fP, int \fIvalue\fP);
.fi
.SH DESCRIPTION
The
\fIgetpriority\fR()
function shall obtain the nice value of a process, process group, or
user. The
\fIsetpriority\fR()
function shall set the nice value of a process, process group, or user
to
.IR value +\c
{NZERO}.
.P
Target processes are specified by the values of the
.IR which
and
.IR who
arguments. The
.IR which
argument may be one of the following values: PRIO_PROCESS, PRIO_PGRP,
or PRIO_USER, indicating that the
.IR who
argument
is to be interpreted as a process ID, a process group ID, or an
effective user ID, respectively. A 0 value for the
.IR who
argument specifies the current process, process group, or user.
.P
The nice value set with
\fIsetpriority\fR()
shall be applied to the process. If the process is multi-threaded,
the nice value shall affect all system scope threads in the process.
.P
If more than one process is specified,
\fIgetpriority\fR()
shall return value
{NZERO}
less than the lowest nice value pertaining to any of the specified
processes, and
\fIsetpriority\fR()
shall set the nice values of all of the specified processes to
.IR value +\c
{NZERO}.
.P
The default nice value is
{NZERO};
lower nice values shall cause more favorable scheduling. While the
range of valid nice values is [0,{NZERO}*2\(mi1], implementations may
enforce more restrictive limits. If
.IR value +\c
{NZERO}
is less than the system's lowest supported nice value,
\fIsetpriority\fR()
shall set the nice value to the lowest supported value; if
.IR value +\c
{NZERO}
is greater than the system's highest supported nice value,
\fIsetpriority\fR()
shall set the nice value to the highest supported value.
.P
Only a process with appropriate privileges can lower its nice value.
.P
Any processes or threads using SCHED_FIFO or SCHED_RR shall be
unaffected by a call to
\fIsetpriority\fR().
This is not considered an error. A process which subsequently reverts
to SCHED_OTHER need not have its priority affected by such a
\fIsetpriority\fR()
call.
.P
The effect of changing the nice value may vary depending on the
process-scheduling algorithm in effect.
.P
Since
\fIgetpriority\fR()
can return the value \(mi1 upon successful completion, it is necessary to
set
.IR errno
to 0 prior to a call to
\fIgetpriority\fR().
If
\fIgetpriority\fR()
returns the value \(mi1, then
.IR errno
can be checked to see if an error occurred or if the value is a
legitimate nice value.
.SH "RETURN VALUE"
Upon successful completion,
\fIgetpriority\fR()
shall return an integer in the range \(mi{NZERO} to
{NZERO}\(mi1.
Otherwise, \(mi1 shall be returned and
.IR errno
set to indicate the error.
.P
Upon successful completion,
\fIsetpriority\fR()
shall return 0; otherwise, \(mi1 shall be returned and
.IR errno
set to indicate the error.
.br
.SH ERRORS
The
\fIgetpriority\fR()
and
\fIsetpriority\fR()
functions shall fail if:
.TP
.BR ESRCH
No process could be located using the
.IR which
and
.IR who
argument values specified.
.TP
.BR EINVAL
The value of the
.IR which
argument was not recognized, or the value of the
.IR who
argument is not a valid process ID, process group ID, or user ID.
.P
In addition,
\fIsetpriority\fR()
may fail if:
.TP
.BR EPERM
A process was located, but neither the real nor effective user ID of
the executing process match the effective user ID of the process whose
nice value is being changed.
.TP
.BR EACCES
A request was made to change the nice value to a lower numeric value
and the current process does not have appropriate privileges.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
.SS "Using getpriority(\|)"
.P
The following example returns the current scheduling priority for the
process ID returned by the call to
\fIgetpid\fR().
.sp
.RS 4
.nf
\fB
#include <sys/resource.h>
\&...
int which = PRIO_PROCESS;
id_t pid;
int ret;
.P
pid = getpid();
ret = getpriority(which, pid);
.fi \fR
.P
.RE
.SS "Using setpriority(\|)"
.P
The following example sets the priority for the current process ID to
\(mi20.
.sp
.RS 4
.nf
\fB
#include <sys/resource.h>
\&...
int which = PRIO_PROCESS;
id_t pid;
int priority = -20;
int ret;
.P
pid = getpid();
ret = setpriority(which, pid, priority);
.fi \fR
.P
.RE
.SH "APPLICATION USAGE"
The
\fIgetpriority\fR()
and
\fIsetpriority\fR()
functions work with an offset nice value (nice value \(mi{NZERO}). The
nice value is in the range [0,2*{NZERO} \(mi1], while the return value
for
\fIgetpriority\fR()
and the third parameter for
\fIsetpriority\fR()
are in the range [\(mi{NZERO},{NZERO} \(mi1].
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fInice\fR\^(\|)",
.IR "\fIsched_get_priority_max\fR\^(\|)",
.IR "\fIsched_setscheduler\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2008,
.IR "\fB<sys_resource.h>\fP"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

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