1.\" Copyright (c) 1994, Henrik Vestergaard Draboel 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by Henrik Vestergaard Draboel. 15.\" 4. The name of the author may not be used to endorse or promote products 16.\" derived from this software without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" $FreeBSD: src/lib/libc/sys/rtprio.2,v 1.13.2.9 2001/12/14 18:34:01 ru Exp $ 31.\" $DragonFly: src/lib/libc/sys/rtprio.2,v 1.4 2006/02/17 19:35:06 swildner Exp $ 32.\" 33.Dd July 23, 1994 34.Dt RTPRIO 2 35.Os 36.Sh NAME 37.Nm rtprio 38.Nd examine or modify a process realtime or idle priority 39.Sh LIBRARY 40.Lb libc 41.Sh SYNOPSIS 42.In sys/types.h 43.In sys/rtprio.h 44.Ft int 45.Fn rtprio "int function" "pid_t pid" "struct rtprio *rtp" 46.Sh DESCRIPTION 47.Fn rtprio 48is used to lookup or change the realtime or idle priority of a process. 49.Pp 50.Fa function 51specifies the operation to be performed. 52RTP_LOOKUP to lookup the current priority, 53and RTP_SET to set the priority. 54.Fa pid 55specifies the process to be used, 0 for the current process. 56.Pp 57.Fa *rtp 58is a pointer to a struct rtprio which is used to specify the priority and priority type. 59This structure has the following form: 60.Bd -literal 61struct rtprio { 62 u_short type; 63 u_short prio; 64}; 65.Ed 66.Pp 67The value of the 68.Nm type 69field may be RTP_PRIO_REALTIME for realtime priorities, 70RTP_PRIO_NORMAL for normal priorities, and RTP_PRIO_IDLE for idle priorities. 71The priority specified by the 72.Nm prio 73field ranges between 0 and 74.Dv RTP_PRIO_MAX (usually 31) . 750 is the highest possible priority. 76.Pp 77Realtime and idle priority is inherited through fork() and exec(). 78.Pp 79A realtime process can only be preempted by a process of equal or 80higher priority, or by an interrupt; idle priority processes will run only 81when no other real/normal priority process is runnable. 82Higher real/idle priority processes 83preempt lower real/idle priority processes. 84Processes of equal real/idle priority are run round-robin. 85.Sh RETURN VALUES 86.Rv -std rtprio 87.Sh ERRORS 88.Fn rtprio 89will fail if 90.Bl -tag -width Er 91.It Bq Er EINVAL 92The specified 93.Fa prio 94was out of range. 95.It Bq Er EPERM 96The calling process is not allowed to set the realtime priority. 97Only 98root is allowed to change the realtime priority of any process, and non-root 99may only change the idle priority of the current process. 100.It Bq Er ESRCH 101The specified process was not found. 102.El 103.Sh SEE ALSO 104.Xr nice 1 , 105.Xr ps 1 , 106.Xr rtprio 1 , 107.Xr setpriority 2 , 108.Xr nice 3 , 109.Xr renice 8 110.Sh AUTHORS 111.An -nosplit 112The original author was 113.An Henrik Vestergaard Draboel Aq hvd@terry.ping.dk . 114This implementation was substantially rewritten by 115.An David Greenman . 116