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