1.\" 2.\" Copyright (c) 1994, Henrik Vestergaard Draboel 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 3. All advertising materials mentioning features or use of this software 14.\" must display the following acknowledgement: 15.\" This product includes software developed by Henrik Vestergaard Draboel. 16.\" 4. The name of the author may not be used to endorse or promote products 17.\" derived from this software without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" $FreeBSD$ 32.\" 33.Dd September 29, 2012 34.Dt RTPRIO 1 35.Os 36.Sh NAME 37.Nm rtprio , 38.Nm idprio 39.Nd execute, examine or modify a utility's or process's realtime 40or idletime scheduling priority 41.Sh SYNOPSIS 42.Nm [id|rt]prio 43.Nm [id|rt]prio 44.Oo Fl Oc Ns Ar pid 45.Nm [id|rt]prio 46.Ar priority 47.Ar command 48.Op args 49.Nm [id|rt]prio 50.Ar priority 51.Fl Ar pid 52.Nm [id|rt]prio 53.Fl t 54.Ar command 55.Op args 56.Nm [id|rt]prio 57.Fl t 58.Fl Ar pid 59.Sh DESCRIPTION 60The 61.Nm 62utility is used for controlling realtime process scheduling. 63.Pp 64The 65.Nm idprio 66utility is used for controlling idletime process scheduling, and can be called 67with the same options as 68.Nm . 69.Pp 70A process with a realtime priority is not subject to priority 71degradation, and will only be preempted by another process of equal or 72higher realtime priority. 73.Pp 74A process with an idle priority will run only when no other 75process is runnable and then only if its idle priority is equal or 76greater than all other runnable idle priority processes. 77.Pp 78Both 79.Nm 80or 81.Nm idprio 82when called without arguments will return the realtime priority 83of the current process. 84.Pp 85If 86.Nm 87is called with 1 argument, it will return the realtime priority 88of the process with the specified 89.Ar pid . 90.Pp 91If 92.Ar priority 93is specified, the process or program is run at that realtime priority. 94If 95.Fl t 96is specified, the process or program is run as a normal (non-realtime) 97process. 98.Pp 99If 100.Ar -pid 101is specified, the process with the process identifier 102.Ar pid 103will be modified, else if 104.Ar command 105is specified, that program is run with its arguments. 106.Pp 107.Ar Priority 108is an integer between 0 and RTP_PRIO_MAX (usually 31). 1090 is the 110highest priority 111.Pp 112.Ar Pid 113of 0 means "the current process". 114.Pp 115Only root is allowed to set realtime or idle priority for a process. 116A user may modify the idle priority of their own processes if the 117.Xr sysctl 8 118variable 119.Va security.bsd.unprivileged_idprio 120is set to non-zero. 121Note that this increases the chance that a deadlock can occur 122if a process locks a required resource and then does 123not get to run. 124.Sh EXIT STATUS 125If 126.Nm 127execute a command, the exit value is that of the command executed. 128In all other cases, 129.Nm 130exits 0 on success, and 1 for all other errors. 131.Sh EXAMPLES 132To see which realtime priority the current process is at: 133.Dl rtprio 134.Pp 135To see which realtime priority of process 1423: 136.Dl "rtprio 1423" 137.Pp 138To run 139.Xr cron 8 140at the lowest realtime priority: 141.Dl "rtprio 31 cron" 142.Pp 143To change the realtime priority of process 1423 to 16: 144.Dl "rtprio 16 -1423" 145.Pp 146To run 147.Xr tcpdump 1 148without realtime priority: 149.Dl "rtprio -t tcpdump" 150.Pp 151To change the realtime priority of process 1423 152to 153.Dv RTP_PRIO_NORMAL 154(non-realtime/normal priority): 155.Dl "rtprio -t -1423" 156.Pp 157To make depend while not disturbing other machine usage: 158.Dl "idprio 31 make depend" 159.Sh SEE ALSO 160.Xr nice 1 , 161.Xr ps 1 , 162.Xr rtprio 2 , 163.Xr setpriority 2 , 164.Xr nice 3 , 165.Xr renice 8 166.Sh HISTORY 167The 168.Nm 169utility appeared in 170.Fx 2.0 , 171but is similar to the HP-UX version. 172.Sh AUTHORS 173.An -nosplit 174.An Henrik Vestergaard Draboel Aq Mt hvd@terry.ping.dk 175is the original author. 176This 177implementation in 178.Fx 179was substantially rewritten by 180.An David Greenman . 181.Sh CAVEATS 182You can lock yourself out of the system by placing a cpu-heavy 183process in a realtime priority. 184.Sh BUGS 185There is no way to set/view the realtime priority of process 0 186(swapper) (see 187.Xr ps 1 ) . 188.Pp 189There is in 190.Fx 191no way to ensure that a process page is present in memory therefore 192the process may be stopped for pagein (see 193.Xr mprotect 2 , 194.Xr madvise 2 ) . 195.Pp 196Under 197.Fx 198system calls are currently never preempted, therefore non-realtime 199processes can starve realtime processes, or idletime processes can 200starve normal priority processes. 201