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The One Key Combination That Rescues a Linux Machine When Everything Is Frozen
Magic SysRq and the REISUB sequence for a safe emergency reboot
Your screen stops moving. The mouse pointer sits still. You press Ctrl+Alt+Delete and nothing happens. You press Caps Lock and the light does not even blink.
You do what everyone does. You hold the power button until the machine dies.
It works. It also risks your data. Files that were half written stay half written. Your filesystem may need repairs on the next boot. A browser session or a database can come back damaged.
Linux has a better way. It is built into the kernel and it works even when your desktop is dead. It is called the Magic SysRq key.
What the SysRq Key Is
Look at the top right of your keyboard. Next to Print Screen you often see a second label that says SysRq. It is short for System Request. On many keyboards it is the same physical key as Print Screen.
The key is a direct line to the Linux kernel. When you press it together with Alt and one more letter the kernel receives a command. The kernel does not need your desktop to be alive. It does not need your terminal. It only needs to be running.
