How can I free space in oracle mount point (/u01/app/oracle/)?
If your oracle installation is on your root volume you should have a look at the DIAG_DESTINATION, e.g. /u01/app/oracle/diag/. If there's a lot of old trace files in there you can safely remove them with adrci. If your oracle installation is on a separate disk you have to check where the space is consumed (/var?) and free space there.