36

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 
4
  • The downside of the fall of /etc/mtab is /dev got unmounted.
    – Joshua
    Jun 22, 2020 at 16:50
  • 1
    You're lucky. I once did rm -rf * in the / directory when I thought I was in a subdirectory.
    – O. Jones
    Jun 24, 2020 at 19:46
  • No worries (in this case). The most important lesson: be very careful of what you do as the root user (i.e. when using sudo). As @O.Jones mentioned, there are worse things you could have done than this.
    – jrw32982
    Jun 25, 2020 at 22:36
  • How could you do that? On my newer system it outputted "/dev: target is busy." - same for many others inc. "/run" and the system is usable. Feb 8, 2023 at 8:22

3 Answers 3

93

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

2
  • 24
    Reboot worked. I have much to learn... Jun 22, 2020 at 0:29
  • When in doubt, turn it off and then on again. (With certain exceptions.)
    – Vikki
    Jun 25, 2020 at 20:41
25

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.

9
  • 1
    REISUB is easier to remember as BUSIER backwards.
    – cjm
    Jun 24, 2020 at 5:02
  • 15
    Reboot Even If System's Utterly Broken
    – Nmath
    Jun 24, 2020 at 6:13
  • 2
    @cjm I think the difficulty with getting it right has little to do with remembering the “REISUB” part, but the alt+SysRq one (or, what key SysRq even is, because it's by no means labelled on all keyboards). Jun 24, 2020 at 8:31
  • 1
    How would you do it remotely over SSH? Jun 25, 2020 at 3:07
  • 1
    @CanadianLuke Is it even possible to be still connected to the machine if you do what OP has done remotely?
    – gerrit
    Jun 25, 2020 at 6:43
-2

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

1
  • 2
    As per the question, sudo produces 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? error.
    – Kulfy
    Jul 21, 2020 at 15:27

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