libc/sys/getpriority.2

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.\"     @(#)getpriority.2	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt GETPRIORITY 2
.Os
.Sh NAME
.Nm getpriority ,
.Nm setpriority
.Nd get/set program scheduling priority
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/time.h
.In sys/resource.h
.Ft int
.Fn getpriority "int which" "int who"
.Ft int
.Fn setpriority "int which" "int who" "int prio"
.Sh DESCRIPTION
The scheduling
priority of the process, process group, or user, as indicated by
.Fa which
and
.Fa who
is obtained with the
.Fn getpriority
system call and set with the
.Fn setpriority
system call.
The
.Fa which
argument
is one of
.Dv PRIO_PROCESS ,
.Dv PRIO_PGRP ,
or
.Dv PRIO_USER ,
and
.Fa who
is interpreted relative to
.Fa which
(a process identifier for
.Dv PRIO_PROCESS ,
process group
identifier for
.Dv PRIO_PGRP ,
and a user ID for
.Dv PRIO_USER ) .
A zero value of
.Fa who
denotes the current process, process group, or user.
The
.Fa prio
argument
is a value in the range -20 to 20.
The default priority is 0;
lower priorities cause more favorable scheduling.
.Pp
The
.Fn getpriority
system call returns the highest priority (lowest numerical value)
enjoyed by any of the specified processes.
The
.Fn setpriority
system call sets the priorities of all of the specified processes
to the specified value.
Only the super-user may lower priorities.
.Sh RETURN VALUES
Since
.Fn getpriority
can legitimately return the value -1, it is necessary
to clear the external variable
.Va errno
prior to the
call, then check it afterward to determine
if a -1 is an error or a legitimate value.
.Pp
.Rv -std setpriority
.Sh ERRORS
The
.Fn getpriority
and
.Fn setpriority
system calls
will fail if:
.Bl -tag -width Er
.It Bq Er ESRCH
No process was located using the
.Fa which
and
.Fa who
values specified.
.It Bq Er EINVAL
The
.Fa which
argument
was not one of
.Dv PRIO_PROCESS ,
.Dv PRIO_PGRP ,
or
.Dv PRIO_USER .
.El
.Pp
In addition to the errors indicated above,
.Fn setpriority
will fail if:
.Bl -tag -width Er
.It Bq Er EPERM
A process was located, but neither its effective nor real user
ID matched the effective user ID of the caller.
.It Bq Er EACCES
A non super-user attempted to lower a process priority.
.El
.Sh SEE ALSO
.Xr nice 1 ,
.Xr fork 2 ,
.Xr renice 8
.Sh HISTORY
The
.Fn getpriority
system call appeared in
.Bx 4.2 .