How to enable safe reboot with reisub

TL;DR

echo "kernel.sysrq = 1" >> /etc/sysctl.d/99-sysctl.conf

When the system hangs:

• alt-sysrq-r - take control of keyboard back from X
• alt-sysrq-e - terminate all processes except init
• alt-sysrq-i - kill all processes except init
• alt-sysrq-s - sync all mounted filesystems
• alt-sysrq-u - remount all mounted filesystems in read-only mode
• alt-sysrq-b - reboot

If there is no sysrq key, use alt-printscreen instead:

• alt-prtscr-r
• alt-prtscr-e
• alt-prtscr-i
• alt-prtscr-s
• alt-prtscr-u
• alt-prtscr-b

Explanation

When the system freezes completely and no other methods(such as ctrl-alt-f3 to open tty) work, it can be tempting to force reboot. However it can be not safe, and it's better to try and use the reisub method.

reisub is a mnemonic for remembering the sequence of keys to press to reboot safely, using OS's methods.

Hold down the alt and sysrq keys, and while holding them down, type the following keys in order, waiting a few seconds between each key:

• alt-sysrq-r - take control of keyboard back from X
• alt-sysrq-e - terminate all processes except init
• alt-sysrq-i - kill all processes except init
• alt-sysrq-s - sync all mounted filesystems
• alt-sysrq-u - remount all mounted filesystems in read-only mode
• alt-sysrq-b - reboot

If there is no sysrq key, use alt-printscreen instead:

• alt-prtscr-r
• alt-prtscr-e
• alt-prtscr-i
• alt-prtscr-s
• alt-prtscr-u
• alt-prtscr-b

On some systems this may not work, so use the command below to enable it for the future:

echo "kernel.sysrq = 1" >> /etc/sysctl.d/99-sysctl.conf

Sometimes just the rei part is enough to just kill all processes without rebooting