int
getpriority(int which, id_t who)
int
setpriority(int which, id_t who, int prio)
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.
A value of 19 or 20
will schedule a process only when nothing at priority 0 is runnable.
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.
)
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.
)
and
setpriority()
will fail if:
ESRCH]which
and
who
values specified.
EINVAL]which
was not one of
PRIO_PROCESS,
PRIO_PGRP,
or
PRIO_USER.
)
will fail if:
EPERM]EACCES])
function call appeared in
4.2BSD.