Using file to designate shared memory to the file.

ftok

• “a.c” → ftok → key
• returns numeric key associated with the file

shmget

• key → shmget → block
• use the key to create or get block of shared memory

shmat

• block→ shmat → ptr
• uses the block id to map the block in the processes’ address space and give us a pointer to the block

This is used for semahpores WOWOW