RTPRIO(1) FreeBSD General Commands Manual RTPRIO(1)
rtprio, idprio -- execute, examine or modify a utility's or process's
realtime or idletime scheduling priority
[id|rt]prio priority command [args]
[id|rt]prio priority -pid
[id|rt]prio -t command [args]
[id|rt]prio -t -pid
The rtprio utility is used for controlling realtime process scheduling.
The idprio utility is used for controlling idletime process scheduling,
and can be called with the same options as rtprio.
A process with a realtime priority is not subject to priority degrada-
tion, and will only be preempted by another process of equal or higher
A process with an idle priority will run only when no other process is
runnable and then only if its idle priority is equal or greater than all
other runnable idle priority processes.
Both rtprio or idprio when called without arguments will return the real-
time priority of the current process.
If rtprio is called with 1 argument, it will return the realtime priority
of the process with the specified pid.
If priority is specified, the process or program is run at that realtime
priority. If -t is specified, the process or program is run as a normal
If -pid is specified, the process with the process identifier pid will be
modified, else if command is specified, that program is run with its
Priority is an integer between 0 and RTP_PRIO_MAX (usually 31). 0 is the
Pid of 0 means "the current process".
Only root is allowed to set realtime or idle priority for a process.
If rtprio execute a command, the exit value is that of the command exe-
cuted. In all other cases, rtprio exits 0 on success, and 1 for all
To see which realtime priority the current process is at:
To see which realtime priority of process 1423:
To run cron(8) at the lowest realtime priority:
rtprio 31 cron
To change the realtime priority of process 1423 to 16:
rtprio 16 -1423
To run tcpdump(1) without realtime priority:
rtprio -t tcpdump
To change the realtime priority of process 1423 to RTP_PRIO_NORMAL (non-
rtprio -t -1423
To make depend while not disturbing other machine usage:
idprio 31 make depend
nice(1), ps(1), rtprio(2), setpriority(2), nice(3), renice(8)
The rtprio utility appeared in FreeBSD 2.0, but is similar to the HP-UX
You can lock yourself out of the system by placing a cpu-heavy process in
a realtime priority.
Henrik Vestergaard Draboel is the original author.
This implementation in FreeBSD was substantially rewritten by David
There is no way to set/view the realtime priority of process 0 (swapper)
There is in FreeBSD no way to ensure that a process page is present in
memory therefore the process may be stopped for pagein (see mprotect(2),
Under FreeBSD system calls are currently never preempted, therefore non-
realtime processes can starve realtime processes, or idletime processes
can starve normal priority processes.
FreeBSD 6.1 July 23, 1994 FreeBSD 6.1