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John
Asked: 2013-09-10 23:37:02 +0800 CST

Reboot linux server with no root filesystem mounted

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I was recently asked the following question:

How could you reboot the linux server if your root filesystem is not mounted and you cannot mount it (it is lost) and you do not have any binary - you have only root shell.

It has something to do with /proc I assume, but maybe it is not possible at all. Could anyone provide some guidance on what I should do in that situation?

linux

2 Answers

  1. You can reboot with magic sysrq key:

    echo b > /proc/sysrq-trigger

    For more information read wiki or kernel documentation.

    echo is also a shell built-in command (known in bash and dash for me) and used if /bin/echo is not available.

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  2. Best Answer

    If you don't have the root file system, and as it was specified in the question, you don't neither have binary, I think that echo will not work, so the only solution is a hardware keyboard interrupt using indeed as said it @Pazi the SysRQ Magic Keys.

    To do so, you should do: Alt+Print Screen / SysRq+some key

    Here, it would be: Alt+Print Screen / SysRq+b (where b will immediately reboot the system, without unmounting or syncing filesystems).

    For additional magic keys and what they do, see Wikipedia: Magic SysRq key. Also note that non-QWERTY layouts may use other physical keys.

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