Ubuntu filesystem not writable

Question

We have a strange problem with Ubuntu filesystem. The problem is, I cant completely reconstruct what happend. The user said, he wanted to format a usb disk. From the bash history I could see, that he installed gnome-disk-utility. He said, that he might have accidently formatted not the usb disk but the system disk or anything else.

However, the system disk is still there, we can log in but only to the shell because X wont start (but the luks GUI screen does, is it independent from X?). When we try startx we get error message, that X cant write a lock file.

However, I tried to write any file with touch in the home folder, but that does not work, even not with sudo because the system is not writable. So because its a (relatively new) SSD I assumed, that there happened a lot write commands and therefore the disk died in a way and is only readable on a hardware basis. But when I connect the disk as an external to another computer, I can write to it.

So, what might have happened, that the filesystem is not writable, even for sudo?

thats all I can find in fstab that is not comments:

$ cat /etc/fstab
UUID=XXX /boot ext2 defaults 0 2
/dev/mapper/it--vg-swap_1 none swap sw 0 0

edit: Ok it really looks like it is a mount problem, I did mount -o remount,rw / and suddenly the system started. Cool. But how can I make this solid for the booting?

Answer 1

ok, the problem was, that the / was mounted readonly when booting. Therefore I set the line:

/dev/mapper/ubuntu--vg-root / ext4 defaults

in /etc/fstab. But I still don't understand why that happened, because there is no other line in fstab that would mount root as readonly.