Buried in the Wikipedia article is what I remember, with a note saying not to use it any more.

So what sysreq keys do you use to recover a non responsive system with a journaling file system?

Before the advent of journaled filesystems a common use of the magic SysRq key was to perform a safe reboot of a locked-up Linux computer (using the sequence of key presses indicated by the mnemonic REISUB), which lessened the risk of filesystem corruption. With modern filesystems, syncing and unmounting is still useful to force unflushed data to disk, but is no longer necessary to prevent filesystem corruption (and may increase the risk of corruption in case the lock-up is caused by the kernel being in a bad state).[11] The default value of kernel.sysrq in distributions such as Ubuntu and Debian remains 176[1]^ (allowing the sync, unmount, and reboot functions) and 438[12] (allowing the same functions plus loglevel, unraw, and nice-all-RT-tasks) respectively.

  1. citation needed ↩︎

  • Maki@lemmy.blahaj.zone
    21·
    22 hours ago

    In case anyone needed a better explanation of what REISUB stands for:

    R.E.I.S.U.B.

    Raising Elephants Is So Utterly Boring

    R.E.I.S.U.B. is a key sequence used on Linux systems to safely reboot a frozen or unresponsive computer. It is often referred to as the “magic SysRq key” (System Request key) and allows users to perform low-level commands to safely recover or restart the system.

    The acronym R.E.I.S.U.B. stands for the specific sequence of commands you can execute to reboot the system safely, even if the system is otherwise unresponsive:

    R - Raw mode (take control of the keyboard back from the X server). E - End all running processes cleanly (sends SIGTERM to all processes). I - Immediately kill all processes (sends SIGKILL to all processes). S - Sync the disk (flushes data to disk to prevent data loss). U - Unmount all file systems (remounts all filesystems as read-only). B - Boot (reboots the system).

    How to Use R.E.I.S.U.B. Safely

    Hold Alt and SysRq, and then press each letter separately in the order of R-E-I-S-U-B. However, often the SysRq key is a dual purpose key which needs another key to activate the secondary function. For example, on a Acer keyboard SysRq is a secondary function of the Delete key and the Fn key is used to select the secondary function. So on this keyboard it would require holding down the Alt + Fn + Delete to activate the SysRq function.

    From http://pclosusers.com/wiki/index.php?title=REISUB_reboot_your_system>

    • exu@feditown.comEnglish
      8·
      20 hours ago

      I’ve always translated R.E.I.S.U.B to Reboot Even If System Utterly Broken

      • imecth@fedia.io
        4·
        19 hours ago

        It doesn’t always work though, if it’s linux itself crashing you’re out of luck.