Instance is down although there is process attached to shared memory

While trying to start the instance INSTANCE001, getting below error, where cache.shid file doesnot contains anything.

This is in a Linux server.

Any help is appreciated.

$ ccontrol start INSTANCE001

INSTANCE001 startup failed: Instance is down although there is process attached to shared memory

You can get the shared memory ID in cache.shid file

then run 'ipcs -m -a' to see the number of processes still attached.