So I was at the data center playing with virtual drives for my Fedora Guest OS. I had to remove an attached virutal drive to clone a guest os. When i tried booting up Fedora the OS was stuck in recovery mode and the entire file system was read only!

Issue: I forgot to comment out the removed drive’s  entry from /etc/fstab file which takes care of all the mount points. Now system was unable to boot the system because it was reading /etc/fstab file was unable to find the device for it.

Linux gives you a “Repair Filesystem” prompt in this situation and you can enter that by providing the root password. The problem is that on “Repair Filesystem” prompt, linux file system and rest of the file systems are generally not mounted and if mounted then it is “Read-Only” so you can not change files.

Solution: Use following command to mount the filesystem with writable permission:

Repair filesystem # mount -w -o remount /

After this you can go and change /etc/fstab file. Restart your computer and that’s it.

extracted from http://thuannvn.blogspot.com/2009/04/how-to-edit-etcfstab-when-at.html