How to list processes attached to a shared memory segment in Linux?__linux

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[Question]:

How do I determine what process are attached to a shared memory segment?

awagner@tree:/home/awagner$ ipcs-m

------Shared Memory segments--------
key        shmid      owner      perms      bytes      nattch     status      
0x00000000 0          Root       777        102400     1                       
0x00000000 32769      Root       774         1          dest         
0x00000000 98306      awagner     2          dest         
0x00000000 131075     awagner        393216     2          dest    

i.e. how did I figure out which two processes are attached to segment 98305?

[Answer]:

I don ' t have the standard tools. You can use the process ID of thelast process to Attach/detach but I ' m not aware of IPCS-MP D processes with IPCS.

With a two-process-attached segment, assuming they both stayed-attached, you can possibly figure out of the creator PID Cpid and last-attached PID lpid which are "two processes but that won" T scale to-more than two-so its processes The ESS is limited.

The Cat/proc/sysvipc/shm method seems similarly limited but I believe there ' s a way to do it with other parts of The/pro c filesystem, as shown below:

When I does a grep on the PROCFS maps to all processes, I get entries containing lines for the Cpidand lpid.

For example, I get the following shared memory segment from IPCS-M:

------Shared Memory Segments--------
key        shmid      owner      perms      bytes      nattch     status      
0x00000000 123456     pax        1024       2          dest

And, from IPCS-MP, the cpid are 3956 and the lpid is 9999 to that given shared memory segment (123456).

Then, with the command grep 123456/proc/*/maps, I:

/proc/3956/maps:blah blah blah 123456/sysv000000 (deleted)/proc/9999/maps:blah blah blah 123456/sysv000000
(dele Ted

So there are a way to get the processes which attached to it. I m pretty certain that dest status and (deleted) indicator are because the creator has marked the segment for destruct Ion once the final detach occurs, not that it ' s already been.

So, by scanning of the/proc/*/maps ' files ', you are should be able to discover-which PIDs are currently to a attached s Egment.

Cpid (-P,-a) The process ID of the job that created the shared memory segment.

Lpid (-P,-a) The process ID of the last job to attach or detach from the shared memory segment or change the semaphore value.