I upgraded my OpenSuse Linux to 15.3 and the "/" root had a little too few diskspace left, so i decided to move /usr to a new device. I copied all files from /usr to the new device, edited the /etc/fstab to update that in the fstab and bootet.
Then, the system used the new device for /usr
/dev/sda3 .... .... 22% /usr
All went without difficulty. With one minor shortage: Root / had the same fill level as before. (Because the "old" /usr was still under the device (mounting of the new /usr was disguising the old /usr only). So i booted into single user mode to get rid of the old /usr, and while several processes also are working in single user mode on /usr (which i didnt aspect) i umounted it with
ummount -l /usr (lazy) Moved it to prepare it for later deletion (mv /usr /xusr)
So the entry in /etc/fstab would mount the /usr on /dev/sda3 so i were able to delete /xusr
But after a reboot nothing worked anymore and Linux threw me to a rescue mode with only some commands left (the most important), i could do nothing, there were no fstab anymore, no root, no device, i think it was only the raw kernel.
After some though about my miserable situation and trying, i mounted several devices to /mnt (mount was working) and found finally the original root device and moved xusr back to is old name /usr so kernel could find it at boot time.
My question: How could someone move /usr to a new location? (I found out, that could be impossible because all important system commands would be in that area and kernel would mount /usr in first place, before it could handle the fstab?)
Is it possible?