c - How two non related process know the same key to allocate same shared memory -

c - How two non related process know the same key to allocate same shared memory -

i learning shared memory ipc. have doubt.

q1. shared memory used related , non related process. , process allocate shared memory shemget function. first parameter of function key. how 2 non related process know same key allocate same shared memory.

q2. whane using shmget , shmat function, new or existing(in using ipc_creat | ipc_excl) memory created , mapped process memory space. section of process memory (like heap,bss) shared memory mapped. , in shmat function if pass shmaddr in utilize then, how scheme behave.

q3. utilize case giving fixed memory addredd in shmat.

refering 1:

how 2 non related process know same key allocate same shared memory.

they either told 3rd entidy or communicate (to) each other.

refering 2b:

and in shmat function if pass shmaddr in utilize then, how scheme behave.

shmat() fail , homecoming (void*) -1.

c linux linux-kernel ipc shared-memory