Opatch failed with following error message
Missing command :fuser
Prerequisite check "CheckSystemCommandAvailable" failed.
Go to patch home/bin directory. go to $ORACLE_HOME/bin and create a file with name fuser. This will solve your issue.
chmod 755 fuser
ls -tlr fuser
-rwxr-xr-x 1 dba oinstall 0 Aug 25 01:51 fuser
Re- run opatch session and check.