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Randy Ssusage
Asked: 2020-06-22 14:49:18 +0800 CST

I accidentally ran "sudo umount -a" and now have no access to anything

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Now I can't remount anything and get access back. How can I fix it?

sudo returns

sudo: effective uid is not 0, is /usr/bin/sudo on a filesystem with the 'nosuid' option set or an NFS filesystem without root privileges?

mount returns

mount: failed to read mtab: No such file or directory

If I try to open anything new I get the message

Failed to execute child 
Failed to open PTY: No such file or directory
filesystem root umount

3 Answers

  1. Just reboot the machine. It is just temporarily and the permanent configuration in /etc/fstab is restored upon reboot.

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  2. Whenever you are on a situation like this on Linux, if you want to do a safe reboot, there is the "Magic SysRq key" + REISUB:

    https://en.wikipedia.org/wiki/Magic_SysRq_key

    You need to press: Alt + SysRq and while keeping that pressed type:

    • r: The kernel takes raw control of the keyboard (from X or Wayland)
    • e: Terminate all running programs
    • i: Kill all programs left (except init)
    • s: Sync (flush data to disk)
    • u: unmount (remounts all filesystems readonly)
    • b: reboot

    Keep a few seconds between each typed letter for each of the tasks to complete.

    This is a clean way of directly telling the linux kernel to restart.

    Since you had unmounted all the file systems, the sync and unmount do not make much sense to me, however it is easier to remember the whole sequence than to apply only the parts you need.

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  3. To avoid rebooting, I believe running sudo mount -a should fix it, as it will then run the mounts specified in /etc/fstab

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