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 indi‐
cated by which and who is obtained with the getpriority() call and set
with the setpriority() call. Which is one of PRIO_PROCESS, PRIO_PGRP, or
PRIO_USER, 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, or user. prio is a value in the range -20 to 20. The default
priority is 0; lower priorities cause more favorable scheduling.
The getpriority() call returns the highest priority (lowest numerical
value) enjoyed by any of the specified processes. The setpriority() call
sets the priorities of all of the specified processes to the specified
value. Only the super-user may lower priorities.
Additionally, the current thread or process can be placed in a background
state by specifying PRIO_DARWIN_THREAD or PRIO_DARWIN_PROCESS for which.
Only a value of zero (the current thread or process) is supported for who
when setting or getting background state. prio is either 0 (to remove
current thread from background status) or PRIO_DARWIN_BG (to set current
thread into background state). When a thread or process is in a back‐
ground state the scheduling priority is set to the lowest value, disk IO
is throttled (with behavior similar to using setiopolicy_np(3) to set a
throttleable policy), and network IO is throttled for any sockets opened
after going into background state. Any previously opened sockets are not
affected. The getpriority() call returns 0 when current thread or
process is not in background state or 1 when the current thread is in
background state. Any thread or process can set itself into background
state.
RETURN VALUES
Since getpriority() can legitimately return the value -1, it is necessary
to clear the external variable 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.
ERRORSGetpriority() and setpriority() will fail if:
[EINVAL] Which is not one of PRIO_PROCESS, PRIO_PGRP,
PRIO_USER, PRIO_DARWIN_THREAD, or PRIO_DARWIN_PROCESS.
[EINVAL] Who is not a valid process, process group, or user ID.
[EINVAL] Who is not 0 when which is PRIO_DARWIN_THREAD or
PRIO_DARWIN_PROCESS.
[ESRCH] No process can be located using the which and who val‐
ues 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 effective 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 ALSOnice(1), fork(2), setiopolicy_np(3), compat(5), renice(8)HISTORY
The getpriority() function call appeared in 4.2BSD.
4th Berkeley Distribution June 4, 1993 4th Berkeley Distribution
