.\" Copyright (c) 1994, Henrik Vestergaard Draboel
.\" All rights reserved.
.\" 
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
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.\"    must display the following acknowledgement:
.\" 	This product includes software developed by Henrik Vestergaard Draboel..
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.\" $Id: rtprio.2,v 1.1 1994/09/01 09:52:37 davidg Exp $
.\"
.Dd July 23, 1994
.Dt RTPRIO 2
.Os FreeBSD 1.1.5.1
.Sh NAME
.Nm rtprio
.Nd examine or modify a process realtime scheduling priority
.Sh SYNOPSIS
.Fd #include <sys/resource.h>
.Ft int 
.Fn rtprio "pid_t pid" "int prio"
.Sh DESCRIPTION
Rtprio() is used to change or read the realtime priority of a process.

.Fa pid
specifies the process to be used. If it is 0, the current process will
be used.

.Fa prio
specifies the new priority of the process, or 
.Dv RTPRIO_RTOFF , 
for normal
(non-realtime) priority or 
.Dv RTPRIO_NOCHG
for nochange (se RETURN VALUE).

Legal values of priorities are between 
.Dv RTPRIO_RTMIN (0)
and  
.Dv RTPRIO_RTMAX (31) .
0 is the highest possible priority.

Realtime priority is enherited through fork() and exec().

A realtime process can only be preempted by a process of equal or
higher priority, or an interrupt. Processes of equal realtime priority
are run in a round-robin schedule.
.Sh RETURN VALUES
If errno is not set, the new (or unchanged) realtime priority of the
process is returned.
.Sh ERRORS
.Fn Rtprio
will fail if 
.Bl -tag -width Er
.It Bq Er EINVAL
The specified
.Fa prio
was out of range.
.It Bq Er EPERM
The calling process is not allowed to set the realtime priority. Only
root is allowed to change the realtime priority of any process.
.It Bq Er ESRCH
The specified process was not found.
.Sh AUTHOR
Henrik Vestergaard Draboel - hvd@terry.ping.dk
.Sh SEE ALSO
.Xr rtprio 1 ,
.Xr nice 1 ,
.Xr ps 1 ,
.Xr nice 2 ,
.Xr renice 8