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GETPRIORITY(2) BSD System Calls Manual GETPRIORITY(2)
NAME
getpriority, setpriority -- get/set program scheduling priority
SYNOPSIS
#include <sys/resource.h>
int
getpriority(int which, id_t who);
int
setpriority(int which, id_t who, int prio);
DESCRIPTION
The scheduling priority of the process, process group, or user as indicated by which and who is
obtained with the getpriority() call and set with the setpriority() call. Additionally, the current
thread can be set to background state. Which is one of PRIO_PROCESS, PRIO_PGRP, PRIO_USER, or
PRIO_DARWIN_THREAD, and who is interpreted relative to which (a process identifier for PRIO_PROCESS,
process group identifier for PRIO_PGRP, and a user ID for PRIO_USER). A zero value of who denotes the
current process, process group, user, thread (for PRIO_DARWIN_THREAD). prio is a value in the range
-20 to 20. The default priority is 0; lower priorities cause more favorable scheduling. For PRIO_DAR-WIN_THREAD, PRIO_DARWIN_THREAD,
WIN_THREAD, prio is either 0 (to remove current thread from background status) or PRIO_DARWIN_BG (to
set current thread into background state).
The getpriority() call returns the highest priority (lowest numerical value) enjoyed by any of the
specified processes or for PRIO_DARWIN_THREAD returns 0 when current thread is not in background state
or 1 when the current thread is in background state. The setpriority() call sets the priorities of all
of the specified processes to the specified value. When setting a thread into background state the
scheduling priority is set to lowest value, disk and network IO are throttled. Network IO will be
throttled for any sockets the thread opens after going into background state. Any previously opened
sockets are not affected. Only the super-user may lower priorities, but any thread can set itself into
background state.
RETURN VALUES
Since getpriority() can legitimately return the value -1, it is necessary to clear the external vari-able variable
able errno prior to the call, then check it afterward to determine if a -1 is an error or a legitimate
value. The setpriority() call returns 0 if there is no error, or -1 if there is.
ERRORS
Getpriority() and setpriority() will fail if:
[EINVAL] Which is not one of PRIO_PROCESS, PRIO_PGRP, PRIO_USER, or PRIO_DARWIN_THREAD.
[EINVAL] Who is not a valid process, process group, or user ID.
[EINVAL] Who is not 0 when which is PRIO_DARWIN_THREAD.
[ESRCH] No process can be located using the which and who values specified.
In addition to the errors indicated above, setpriority() will fail if:
[EACCES] A non super-user attempts to lower a process priority.
[EPERM] A process is located, but neither its effective nor real user ID matches the effec-tive effective
tive user ID of the caller.
LEGACY SYNOPSIS
#include <sys/types.h>
#include <sys/resource.h>
The include file <sys/types.h> is necessary.
int
getpriority(int which, int who);
int
setpriority(int which, int who, int value);
The type of who has changed.
SEE ALSO
nice(1), fork(2), compat(5), renice(8)
HISTORY
The getpriority() function call appeared in 4.2BSD.
4th Berkeley Distribution June 4, 1993 4th Berkeley Distribution
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