I've attached a volume to a running instance in order to change the owner of /var directory (I did the mistake of changing the owner of /var and lost the access to the instance).
Running cat /proc/partitions
major minor #blocks name 202 1 8388608 xvda1 202 80 8388608 xvdf
The var directory I want to change the owner is in "xvdf".
How I do it?