rtprio man page on FreeBSD

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RTPRIO(1)		  BSD 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 [-]pid
     [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
     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 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
     (non-realtime) process.

     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
     highest priority

     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
     other errors.

     To see which realtime priority the current process is at:

     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 (non-
     realtime/normal priority):
	   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 ⟨hvd@terry.ping.dk⟩ 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)
     (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),

     Under FreeBSD system calls are currently never preempted, therefore non-
     realtime processes can starve realtime processes, or idletime processes
     can starve normal priority processes.

BSD				 July 23, 1994				   BSD

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