How to drop a DB2 instance when the instance owner was removed
If you dropped the instance from the file system (perhaps while DB2 was down with db2stop), then, DB2 still "knows" about the instance because its directories contain a reference to it.

I would perhaps try to uncatalog the instance first (this would remove it from the directories).

Try the following:

db2 uncatalog node &lt;instance name&gt;;
db2 terminate;


And see if that doens't help. You may also need to remove the instance definition from the DB2 registry:

# make sure there is a space after the equals sign to unassign this variable.
db2set DB2INSTDEF= -g
db2stop
db2start


As with anything, try to take a backup of everything before you mess around so you don't make it worse.