Delete shared memory segments left over by an Oracle instance
I hope that you know what you are doing....

First find which segment would be a candidate to drop because it was not cleaned up by an Oracle crash:

ipcs -bom


Take note of the owner and group, they should be the owner of the Oracle rdbms processes. Next check the NATTCH column, should be 0 processes attached to the segment. If you still want to remove that segment (which is pretty safe when there are no processes attached), use the ID column as input for 

ipcrm -M {your_ID}


Normally this does not solve a problem. There was a problem that made the instance crash .... check the alertlog, it could have some clues in it.