GETPRIORITY
Section: POSIX Programmer's Manual (3P)
Updated: 2013
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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.
NAME
getpriority,
setpriority
--- get and set the nice value
SYNOPSIS
#include <sys/resource.h>
int getpriority(int which, id_t who);
int setpriority(int which, id_t who, int value);
DESCRIPTION
The
getpriority()
function shall obtain the nice value of a process, process group, or
user. The
setpriority()
function shall set the nice value of a process, process group, or user
to
value+{NZERO}.
Target processes are specified by the values of the
which
and
who
arguments. The
which
argument may be one of the following values: PRIO_PROCESS, PRIO_PGRP,
or PRIO_USER, indicating that the
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
who
argument specifies the current process, process group, or user.
The nice value set with
setpriority()
shall be applied to the process. If the process is multi-threaded,
the nice value shall affect all system scope threads in the process.
If more than one process is specified,
getpriority()
shall return value
{NZERO}
less than the lowest nice value pertaining to any of the specified
processes, and
setpriority()
shall set the nice values of all of the specified processes to
value+{NZERO}.
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
value+{NZERO}
is less than the system's lowest supported nice value,
setpriority()
shall set the nice value to the lowest supported value; if
value+{NZERO}
is greater than the system's highest supported nice value,
setpriority()
shall set the nice value to the highest supported value.
Only a process with appropriate privileges can lower its nice value.
Any processes or threads using SCHED_FIFO or SCHED_RR shall be
unaffected by a call to
setpriority().
This is not considered an error. A process which subsequently reverts
to SCHED_OTHER need not have its priority affected by such a
setpriority()
call.
The effect of changing the nice value may vary depending on the
process-scheduling algorithm in effect.
Since
getpriority()
can return the value -1 upon successful completion, it is necessary to
set
errno
to 0 prior to a call to
getpriority().
If
getpriority()
returns the value -1, then
errno
can be checked to see if an error occurred or if the value is a
legitimate nice value.
RETURN VALUE
Upon successful completion,
getpriority()
shall return an integer in the range -{NZERO} to
{NZERO}-1.
Otherwise, -1 shall be returned and
errno
set to indicate the error.
Upon successful completion,
setpriority()
shall return 0; otherwise, -1 shall be returned and
errno
set to indicate the error.
ERRORS
The
getpriority()
and
setpriority()
functions shall fail if:
- ESRCH
-
No process could be located using the
which
and
who
argument values specified.
- EINVAL
-
The value of the
which
argument was not recognized, or the value of the
who
argument is not a valid process ID, process group ID, or user ID.
In addition,
setpriority()
may fail if:
- 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.
- EACCES
-
A request was made to change the nice value to a lower numeric value
and the current process does not have appropriate privileges.
The following sections are informative.
EXAMPLES
Using getpriority()
The following example returns the current scheduling priority for the
process ID returned by the call to
getpid().
-
#include <sys/resource.h>
...
int which = PRIO_PROCESS;
id_t pid;
int ret;
pid = getpid();
ret = getpriority(which, pid);
Using setpriority()
The following example sets the priority for the current process ID to
-20.
-
#include <sys/resource.h>
...
int which = PRIO_PROCESS;
id_t pid;
int priority = -20;
int ret;
pid = getpid();
ret = setpriority(which, pid, priority);
APPLICATION USAGE
The
getpriority()
and
setpriority()
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
getpriority()
and the third parameter for
setpriority()
are in the range [-{NZERO},{NZERO} -1].
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
nice(),
sched_get_priority_max(),
sched_setscheduler()
The Base Definitions volume of POSIX.1-2008,
<sys_resource.h>
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 .
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 .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- Using getpriority()
-
- Using setpriority()
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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