I need to repair the root partition in an Ubuntu 20.04 server. However, I cannot manage to boot the server into rescue or emergency mode and have the root partition read-only to be able to run the checks.

My Grub2 boot menu Linux command line looks like the following

linux /boot/vmlinuz-... root=/dev/mapper/vgname-lvname ro emergency

I also have tried the systemd.unit=emergency.target approach, but this also didn't work.

The console greets me with the correct line:

You are in emergency mode. [...] Give root password for maintenance (or press Control-D to continue):

However, entering the root password and checking the root mount point reveals that root is mounted read-write instead of read-only.

/dev/mapper/vgname-lvname on / type ext4 (rw,relatime,errors=remount-ro)

mount -o remount,ro / (or the LVM volume) fails due to the mount point is busy.

How to force read-only mode in the emergency mode?


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