If two processes attach to the same shared memory segment, is it possible to make shmat() attach the shared memory segment to the same local space address in both processes? In other words, if shmat(shm_id, 0, flags) returns 0xc04ab000 in proc1, I would like shmat() returns the same address in proc2, which is 0xc04ab000.

I could pass 0xc04ab000 as the second parameter when calling shmat(), but since it's from proc1, I have to get it using some sort of IPC. HP-UX returns the same local space address if processes attach to the same segment. Looks like it's not guaranteed in Linux.

To get the same shared memory between two process ,I
think you have to give the same shmid while calling shmat().
So you don't have to pass the address ,you have to pass
the shmid.


Do the following:
1)process1 gets the shared memory by shmget(),
returning a shmid.

2)process1 attaches to the shared memory by shmat() usingthe shmid returned previously.

3)pass the shmid to process2.

4)process2 attaches to the shared memory using the same shmid.

now you are free to use the shared memory as you wish.
then both process should detach themselves and one should release the shared memory.


PS:let us know how you did it

It should work in Unix. In Linux, no.

are you forking the processes?

No, I am not.