man-pages/man3p/getpriority.3p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "GETPRIORITY" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" getpriority 
.SH NAME
getpriority, setpriority \- get and set the nice value
.SH SYNOPSIS
.LP
\fB#include <sys/resource.h>
.br
.sp
int getpriority(int\fP \fIwhich\fP\fB, id_t\fP \fIwho\fP\fB);
.br
int setpriority(int\fP \fIwhich\fP\fB, id_t\fP \fIwho\fP\fB, int\fP
\fIvalue\fP\fB); \fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIgetpriority\fP() function shall obtain the nice value of a
process, process group, or user. The \fIsetpriority\fP()
function shall set the nice value of a process, process group, or
user to \fIvalue\fP+ {NZERO}.
.LP
Target processes are specified by the values of the \fIwhich\fP and
\fIwho\fP arguments. The \fIwhich\fP argument may be one
of the following values: PRIO_PROCESS, PRIO_PGRP, or PRIO_USER, indicating
that the \fIwho\fP argument is to be interpreted as a
process ID, a process group ID, or an effective user ID, respectively.
A 0 value for the \fIwho\fP argument specifies the current
process, process group, or user.
.LP
The nice value set with \fIsetpriority\fP() shall be applied to the
process. If the process is multi-threaded, the nice value
shall affect all system scope threads in the process.
.LP
If more than one process is specified, \fIgetpriority\fP() shall return
value {NZERO} less than the lowest nice value
pertaining to any of the specified processes, and \fIsetpriority\fP()
shall set the nice values of all of the specified processes
to \fIvalue\fP+ {NZERO}.
.LP
The default nice value is {NZERO}; lower nice values shall cause more
favorable scheduling. While the range of valid nice values
is [0,{NZERO}*2-1], implementations may enforce more restrictive limits.
If \fIvalue\fP+ {NZERO} is less than the system's lowest
supported nice value, \fIsetpriority\fP() shall set the nice value
to the lowest supported value; if \fIvalue\fP+ {NZERO} is
greater than the system's highest supported nice value, \fIsetpriority\fP()
shall set the nice value to the highest supported
value.
.LP
Only a process with appropriate privileges can lower its nice value.
.LP
Any processes or threads using SCHED_FIFO or SCHED_RR shall be unaffected
by a call to \fIsetpriority\fP(). This is not considered
an error. A process which subsequently reverts to SCHED_OTHER need
not have its priority affected by such a \fIsetpriority\fP()
call. 
.LP
The effect of changing the nice value may vary depending on the process-scheduling
algorithm in effect.
.LP
Since \fIgetpriority\fP() can return the value -1 on successful completion,
it is necessary to set \fIerrno\fP to 0 prior to a
call to \fIgetpriority\fP(). If \fIgetpriority\fP() returns the value
-1, then \fIerrno\fP can be checked to see if an error
occurred or if the value is a legitimate nice value.
.SH RETURN VALUE
.LP
Upon successful completion, \fIgetpriority\fP() shall return an integer
in the range -{NZERO} to {NZERO}-1. Otherwise, -1 shall
be returned and \fIerrno\fP set to indicate the error.
.LP
Upon successful completion, \fIsetpriority\fP() shall return 0; otherwise,
-1 shall be returned and \fIerrno\fP set to
indicate the error.
.SH ERRORS
.LP
The \fIgetpriority\fP() and \fIsetpriority\fP() functions shall fail
if:
.TP 7
.B ESRCH
No process could be located using the \fIwhich\fP and \fIwho\fP argument
values specified.
.TP 7
.B EINVAL
The value of the \fIwhich\fP argument was not recognized, or the value
of the \fIwho\fP argument is not a valid process ID,
process group ID, or user ID.
.sp
.LP
In addition, \fIsetpriority\fP() may fail if:
.TP 7
.B 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 7
.B EACCES
A request was made to change the nice value to a lower numeric value
and the current process does not have appropriate
privileges.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.SS Using getpriority()
.LP
The following example returns the current scheduling priority for
the process ID returned by the call to \fIgetpid\fP().
.sp
.RS
.nf

\fB#include <sys/resource.h>
\&...
int which = PRIO_PROCESS;
id_t pid;
int ret;
.sp

pid = getpid();
ret = getpriority(which, pid);
\fP
.fi
.RE
.SS Using setpriority()
.LP
The following example sets the priority for the current process ID
to -20.
.sp
.RS
.nf

\fB#include <sys/resource.h>
\&...
int which = PRIO_PROCESS;
id_t pid;
int priority = -20;
int ret;
.sp

pid = getpid();
ret = setpriority(which, pid, priority);
\fP
.fi
.RE
.SH APPLICATION USAGE
.LP
The \fIgetpriority\fP() and \fIsetpriority\fP() functions work with
an offset nice value (nice value -{NZERO}). The nice value
is in the range [0,2*{NZERO} -1], while the return value for \fIgetpriority\fP()
and the third parameter for \fIsetpriority\fP()
are in the range [-{NZERO},{NZERO} -1].
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fInice\fP() , \fIsched_get_priority_max\fP() , \fIsched_setscheduler\fP()
, the Base Definitions volume of IEEE\ Std\ 1003.1-2001, \fI<sys/resource.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .