[Tip] Enable Magic SysRq Key (REISUB)

[smokey]

https://wiki.archlinux.org/title/keyboard_shortcuts

Troubleshooting

• If a SysRq action produces output, it is sent to the kernel ring buffer where the systemd journal will pick it up. When nothing prevents the output to be displayed on the Linux console, it will be there too. Not having a response on the console does not prove the SysRq command was not processed successfully. If that is the case, run journalctl -kf to monitor the output as it arrives to the kernel ring buffer.
• If you are using a display manager and after Alt+SysRq+e you are presented with the login screen (or full desktop if autologin is enabled), it is most likely caused by Restart=always directive in the relevant service file. If necessary, edit the unit, however this should not prevent the “REISUB” sequence from working.
• If all the above combinations work except Alt+SysRq+b, try using the contralateral Alt key.
• On laptops that use Fn key to differentiate SysRq from PrtScrn, it may not actually be necessary to use the Fn key (i.e., Alt+PrtScrn+letter could work).
• On Lenovo laptops (outside of their Legion lineup) SysRq is often configured as Fn+S. To use it press and hold Alt then press Fn+s, release Fn and s still holding Alt followed by the keys above.
• You may need to press Ctrl along with Alt. So for example, full key shortcut would be Ctrl+Alt+SysRq+b.

This is the most useful information I can find so far

[Moshe_Yehudah]

Yeah, it worked!
So I had to hold the Ctrl key as well and it works now
Nice, thanks for your help guys

[smokey]

Nice glad you figured it out

[33Nicolas]

@Kresimir

The Linux kernel authors have provided a very nice feature of issuing low-level commands to the kernel directly, regardless of the state the system is in. This is called the “Magic SysRq Key”, because these commands are issued by pressing the SysRq key on the keyboard (if you can’t find it, typically, it shares the same physical key as the Print Screen key, but on some laptops it can be elsewhere).

A common use is to reboot when the computer freezes and becomes unresponsive due to some software or hardware exception, without having to push the hardware reset button or to cut power to the computer, which runs the risk of corrupting the filesystem and does not give the chance to processes which are still responsive to terminate gracefully. The magic SysRq key lets us do this elegantly and safely.

On EndeavourOS, like on vanilla Arch, this functionality is disabled by default, because it is a potential security concern (however, since it requires physical access to the keyboard, it’s not a big security concern). This is how you enable it:

• Run this command in the terminal:

echo ‘kernel.sysrq=1’ | sudo tee /etc/sysctl.d/99-reisub.conf

This will create the file `/etc/sysctl.d/99-reisub.conf`, containing the single line `kernel.sysrq=1` (it does not have to be named `99-reisub.conf`, but the name is good because you’ll know what it does, it is the location of the file and its contents that are important). Alternatively, you can create this file using a terminal-based text editor, like `vim` or `nano` with `sudo`.
* Reboot for the change to take place.
* If you want to disable this functionality, just remove the file created in the first step (`sudo rm /etc/sysctl.d/99-reisub.conf`)

Now, when you want to hard-reboot the computer, perform the following key combination:
press and hold the <kbd>Alt</kbd> key the entire time. Now, one after another, with about a second in between, press (tap) the following keys: <kbd>SysRq</kbd>, <kbd>R</kbd>, <kbd>E</kbd>, <kbd>I</kbd>, <kbd>S</kbd>, <kbd>U</kbd>, <kbd>B</kbd>. Your computer should reboot if everything was done correctly (you can let go of the <kbd>Alt</kbd> key now :wink: ).

This sequence issues the following low-level commands to the kernel:

* <kbd>R</kbd> = Switch the keyboard from raw mode to XLATE mode
* <kbd>E</kbd> = Send the signal `SIGTERM` to gracefully terminate all processes (except `PID 1`)
* <kbd>I</kbd> = Send the signal `SIGKILL` to kill all processes that didn’t terminate gracefully
* <kbd>S</kbd> = Sync data to disk (flush)
* <kbd>U</kbd> = Unmount the filesystem (and remount as read-only)
* <kbd>B</kbd> = Reboot

Just remember that the letters spell REISUB (a good mnemonic is “Reboot Even If System Utterly Broken”).

For more info, see:
[https://wiki.archlinux.org/index.php/Keyboard_shortcuts#Kernel ](https://wiki.archlinux.org/index.php/Keyboard_shortcuts#Kernel)

[https://www.kernel.org/doc/html/latest/admin-guide/sysrq.html ](https://www.kernel.org/doc/html/latest/admin-guide/sysrq.html)

I can’t thank you enough for that one. I emailed it to myself in case this happens and can see it from another device.

Thanks!

[Granite]

I have a new laptop that does not have the SysRq key, but it does have a PrtSc key.

If I want to runecho 'kernel.sysrq=1' | sudo tee /etc/sysctl.d/99-reisub.conf

does that mean I have to change the 'kernel.sysrq=1' part to 'kernel.prtsc=1'?

[manfredlotz]

No. My understanding is, (as Kresimir said), that the PrtSc key is taken if the SysRq key is not available. So, you don’t want to do kernel.prtsc=1 which doesn’t make much sense.

[Granite]

For the record:

True, it works. Note: as soon as I hit the “I” key the screen goes black, suggesting, to me in any case, the procedure is over. However, despite the screen going black, you have to tap the remainder of the keys too.

[manuel]

Closing this thread so that it doesn’t become too large.
For related messages users can create a new thread and refer to this.