Raising Skinny Elephants Is Utterly Boring
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"Raising Skinny Elephants Is Utterly Boring" is a mnemonic device for remembering a particularly important keystroke sequence in Linux. In the event of a total system freeze up, this is the failsafe way to safely reboot a near-frozen computer. It should be noted that this is a Linux specific feature with potential security issues, so be certain to read about the implications before enabling this on production servers, and that for OS' other than Linux, they probably will respond differently to the SysRq key.
SysRq sequences can be turned on and off at compile time by defining the CONFIG_MAGIC_SYSRQ symbol. While it is required to be compiled in before it can be used, it can also be disabled or enabled at runtime by writing a 0 or 1 (respectively) to /proc/sys/kernel/sysrq or using the sysctl kernel.sysrq.
Finally, for Serial Console users without an appropriate break signal in their terminal may be able to echo the appropriate character-command (one at a time) to /proc/sysrq-trigger.
Most desktop computer systems will have these key combinations enabled by default, but corporate versions often do not.
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[edit] Usage
The first two key sequences to deal with a frozen machine are:
- Alt + Ctrl + <function key> to enter a command prompt. Normally the function keys F1 to F6 can be used.
- Control-Alt-Delete. This performs a regular shutdown, if possible, which allows running services to shut down normally.
Using 'RSEIUB' follows these two steps as a last resort. The sequence is performed as follows: While holding Alt and SysRq, press the keys R, S, E, I, U, and then B, in sequence, leaving some time between keystrokes.
[edit] Meaning
- R places the keyboard in raw mode
- S synchronizes the disk
- E terminates all processes
- I kills all processes
- U remounts all filesystems read-only
- B reboots the machine
[edit] See also
