2nd , to confirm what dilberts_left_nut says
No it is not safe. It should, or probably will give a error, warning you:
" can not umount, " or "device is busy "
Code: Select all
# umount /var
umount: /var: Device busy
If you do manage to figure out how to force it, you are most like likely going to end up with a damaged system, and unable to boot the next time it boots. (been there, and done that) I ended up re-installing a new system.
Fortunately I had made a back up of my important data, but still a lot of hassle, for something that did not work.
Using a "live" USB or CD, that can read/write to the drive, boot with the "live" device, you can then work on the other partition / drive or device without it being mounted.
Even then, it is all ways best to be sure to have a good back up made,
in case things go wrong.