I tried to unmount all of my fstab mounts by using:
sudo umount --all
Right after that i tried to remount everything by using:
sudo mount -a
But got this error:
sudo: effective uid is not 0, is /usr/bin/sudo on a file system with the ‘nosuid’ options set or an NFS file system without root privileges?
Now sudo doesn’t work at all even for simple commands. How could I fix this?
The error message indicates that the mount containing /usr/bin/sudo (i.e. /usr/bin/ or /usr/ or even just /) is mounted with the nosuid option. But without the effective suid bit sudo is unable to change the effective user.
So what probably happened is that umount --all unmounted /usr/bin or /usr/. Now running sudo will execute the binary file /usr/bin/sudo which is placed on the filesystem/mount that was previously covered/overlayed by the now unmounted filesystem at /usr/bin*.
If all you did was sudo umount --all a simple reboot should fix the problem since all configured mounts should be mounted automatically again.
If you can not/do not want to reboot you'll need some other way to execute mount -a as root:
su instead*the filesystem previously mounted at /usr/bin/ may also be the same device but remounted with different options
