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getpriority, setpriority — get/set program scheduling priority
Standard C Library (libc, -lc)
getpriority(int which, int who);
setpriority(int which, int who, int prio);
The scheduling priority of the process, process group, or user, as
indicated by which and who is obtained with the getpriority() system call
and set with the setpriority() system call. The which argument 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. The prio argument is a
value in the range -20 to 20. The default priority is 0; lower
priorities cause more favorable scheduling.
The getpriority() system call returns the highest priority (lowest
numerical value) enjoyed by any of the specified processes. The
setpriority() system call sets the priorities of all of the specified
processes to the specified value. Only the super-user may lower
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() function returns the value 0 if successful; otherwise
the value -1 is returned and the global variable errno is set to indicate
The getpriority() and setpriority() system calls will fail if:
[ESRCH] No process was located using the which and who values
[EINVAL] The which argument was not one of PRIO_PROCESS,
PRIO_PGRP, or PRIO_USER.
In addition to the errors indicated above, setpriority() will fail if:
[EPERM] A process was located, but neither its effective nor
real user ID matched the effective user ID of the
[EACCES] A non super-user attempted to lower a process
nice(1), fork(2), renice(8)
The getpriority() system call appeared in 4.2BSD.