rtprio(1)

NAME

rtprio, idprio - execute, examine or modify a utility's or

process's
realtime or idletime scheduling priority

SYNOPSIS

[id|rt]prio
[id|rt]prio [-]pid
[id|rt]prio priority command [args]
[id|rt]prio priority -pid
[id|rt]prio -t command [args]
[id|rt]prio -t -pid

DESCRIPTION

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 priori

ty degradation, and will only be preempted by another process of equal

or higher
realtime priority.

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 re

turn the realtime priority of the current process.

If rtprio is called with 1 argument, it will return the re

altime 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
(non-realtime) process.

If -pid is specified, the process with the process identifi

er pid will be
modified, else if command is specified, that program is run

with its
arguments.

Priority is an integer between 0 and RTP_PRIO_MAX (usually

31). 0 is the
highest priority

Pid of 0 means "the current process".

Only root is allowed to set realtime or idle priority for a

process.

EXIT STATUS

If rtprio execute a command, the exit value is that of the

command executed. In all other cases, rtprio exits 0 on success, and 1

for all
other errors.

EXAMPLES

To see which realtime priority the current process is at:

rtprio

To see which realtime priority of process 1423:

rtprio 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 (nonrealtime/normal priority):

rtprio -t -1423

To make depend while not disturbing other machine usage:

idprio 31 make depend

SEE ALSO

nice(1), ps(1), rtprio(2), setpriority(2), nice(3),

renice(8)

HISTORY

The rtprio utility appeared in FreeBSD 2.0, but is similar

to the HP-UX
version.

CAVEATS

You can lock yourself out of the system by placing a cpu

heavy process in
a realtime priority.

AUTHORS

Henrik Vestergaard Draboel <hvd@terry.ping.dk> is the origi

nal author.
This implementation in FreeBSD was substantially rewritten

by David
Greenman.

BUGS

There is no way to set/view the realtime priority of process

0 (swapper)
(see ps(1)).

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),
madvise(2)).

Under FreeBSD system calls are currently never preempted,

therefore nonrealtime processes can starve realtime processes, or idle

time processes
can starve normal priority processes.

BSD July 23, 1994

BSD