Sudo – How to Recover from Mounting /usr/ nosuid

fstabsusudo

I was able to move /usrto an external harddrive. In fstab I mistakenly mounted the drive with nosuid. Now I can't use sudo or su. I can't edit the fstab entry. When I manage to open it I can't do so as root and it therefore is read-only. I can provide more details if need be.

How can I fix this?

Best Answer

I'm probably late to the party, but recently I learned that having /usr on a separate partition is not such a good idea anyway - some things during the early Linux boot expect /usr to be available - so generally there will be silent failures unless you also modify the initrd to mount /usr during the early boot:

Most of the failures you will experience with /usr split off and not pre-mounted
in the initramfs are graceful failures: they won't become directly visible, 
however certain features become unavailable due to these failures.
...
Here's a short, very in-comprehensive list of software we are aware that currently
they are not able to provide the full set of functionality when /usr is split off 
and not pre-mounted at boot: udev-pci-db/udev-usb-db and all rules depending on
this (using the PCI/USB database in /usr/share), PulseAudio, NetworkManager, '
ModemManager, udisks, libatasmart, usb_modeswitch, gnome-color-manager, usbmuxd, 
ALSA, D-Bus, CUPS, Plymouth, the locale logic of most programs and a lot of 
other stuff.

See Booting Without /usr is Broken for more details.

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Try adding the "defaults" option

//192.168.1.5/PUBLIC /media/MyBookLive cifs defaults,credentials=/home/gacek/.mybookcredentials,uid=1000,gid=1000

or the "rw" option.

//192.168.1.5/PUBLIC /media/MyBookLive cifs rw,credentials=/home/gacek/.mybookcredentials,uid=1000,gid=1000

Ubuntu – How to Block Automounting of a Specific Drive (USB connection) With Three Mounted Partitions

In the man fstab page we find the noauto parameter...

  The fourth field (fs_mntops).
          This  field  describes  the  mount  options  associated with the
          filesystem.

          It is formatted as a comma-separated list of options.   It  con‐
          tains at least the type of mount (ro or rw), plus any additional
          options appropriate to the filesystem  type  (including  perfor‐
          mance-tuning options).  For details, see mount(8) or swapon(8).

          Basic filesystem-independent options are:

          defaults
                 use  default  options: rw, suid, dev, exec, auto, nouser,
                 and async.

          noauto do not mount when "mount -a"  is  given  (e.g.,  at  boot
                 time)

          user   allow a user to mount

          owner  allow device owner to mount

          comment
                 or x-<name> for use by fstab-maintaining programs

          nofail do  not  report errors for this device if it does not ex‐
                 ist.

Using sudo blkid you can easily determine the proper UUIDs to use.

You'll need to create these entries in /etc/fstab...

sudo -H gedit /etc/fstab

UUID=xxxx-xxxx /media/me/ESP vfat ro,noauto,nofail 0 0
UUID=xxxx-xxxx /media/me/DIAGS vfat ro,noauto,nofail 0 0
UUID=xxxxxxxxxxxxxxxx /media/me/WINRETOOLS ntfs ro,noauto,nofail 0 0
UUID=xxxxxxxxxxxxxxxx /media/me/OS ntfs ro,noauto,nofail 0 0

Update #1:

OP replaced Nautilus file manager with Thunar, and Thunar has a separate option to mount external drives. Disable that, and this all works as expected. Not a standard configuration.

Best Answer

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Ubuntu – How to Block Automounting of a Specific Drive (USB connection) With ** Three Mounted Partitions **

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