The command ipcs produces a list of the IPC resources currently in use:
$ ipcs ------ Shared Memory Segments -------- key shmid owner perms bytes nattch status 0x000027d9 5734403 toms 660 64528 2 0x00000000 5767172 toms 666 37044 2 0x00000000 5799941 toms 666 37044 2 ------ Semaphore Arrays -------- key semid owner perms nsems 0x000027d9 0 toms 660 1 ------ Message Queues -------- key msqid owner perms used-bytes messages