RTPRIO(1)

📦 version 15.1, in freebsd 14.5, freebsd 15.1

🎀 NAME 🎀

okay so RTPRIO(1) — from the General Commands Manual — is literally the page for rtprio and idprio: the utilities that execute, examine, or modify a utility's or process's realtime or idletime scheduling priority. the way that this is both niche and iconic? obsessed. 💅

✨ SYNOPSIS ✨

bestie, here are the exact shapes this thing comes in — no cap:

[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

that's the whole synopsis vibe. ✨

💅 DESCRIPTION 💅

okay so rtprio is the utility for controlling realtime process scheduling. idprio is the sibling for controlling idletime process scheduling, and it can be called with the same options as rtprio. 🫶

A process with a realtime priority is highkey not subject to priority degradation, and will only be preempted by another process of equal or higher realtime priority. it's giving "main character who cannot be interrupted unless someone equally iconic shows up." 👑

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. lowkey the "only when the group chat is dead" energy — and honestly, that constraint ate. 🦋

Both rtprio and idprio, when called without arguments, will return the realtime 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. literally just peeking at the priority, no edits. ✨

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 arguments. so you're either poking an existing process or launching a new one, iykyk. 💅

vibe check: priority is an integer between 0 and RTP_PRIO_MAX (usually 31). 0 is the highest priority. not me thinking 31 would be the top — nope, 0 is the queen. 👑

pid of 0 means “the current process”. 🫶

ngl, only root is allowed to set realtime or idle priority for a process. Exceptional privileges can be granted through the mac_priority(4) policy and the realtime and idletime user groups. The sysctl(8) variable security.bsd.unprivileged_idprio is deprecated. If set to non-zero, it lets any user modify the idle priority of processes they own. 🚨

⚠️ note: idle priority increases the chance that a deadlock can occur if a process locks a required resource and then does not get to run. that's not a vibe, bestie — keep it in mind. 💀

😭 EXIT STATUS 😭

If rtprio executes 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. periodt. ✅

🌈 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 (non-realtime/normal priority): rtprio -t -1423
  • To make depend while not disturbing other machine usage: idprio 31 make depend

👀 SEE ALSO 👀

🧚 HISTORY 🧚

The rtprio utility appeared in FreeBSD 2.0, but is similar to the HP-UX version. nostalgia core. 🕰️

💖 AUTHORS 💖

Henrik Vestergaard Draboel <hvd@terry.ping.dk> is the original author. This implementation in FreeBSD was substantially rewritten by David Greenman. iconic collaboration, honestly. 🫶

🚨 CAVEATS 🚨

You can lock yourself out of the system by placing a cpu-heavy process in a realtime priority. bestie, do not do this casually. 💀

🐛 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 non-realtime processes can starve realtime processes, or idletime processes can starve normal priority processes.

🎀 bye bestie 💖 this page is Debian, dated December 8, 2021, and the manual is RTPRIO(1) — slay responsibly. 🌸

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