How do I determine what process is 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 96 1 dest 0x00000000 98306 awagner 600 393216 2 dest 0x00000000 131075 awagner 600 393216 2 dest
i.e. how do I figure out which two processes are attached to segment 98305?
I don't think you can do this with the standard tools. You can use
ipcs -mp to get the process ID of thelast process to attach/detach but I'm not aware of how to get all attached processes with
With a two-process-attached segment, assuming they both stayed attached, you can possibly figure out from the creator PID
cpid and last-attached PID
lpid which are the two processes but that won't scale to more than two processes so its usefulness is limited.
cat /proc/sysvipc/shm method seems similarly limited but I believe there's a way to do it with other parts of the
/proc filesystem, as shown below:
When I do a
grep on the
procfs maps for all processes, I get entries containing lines for the
For example, I get the following shared memory segment from
------ Shared Memory Segments -------- key shmid owner perms bytes nattch status 0x00000000 123456 pax 600 1024 2 dest
ipcs -mp, the
cpid is 3956 and the
lpid is 9999 for that given shared memory segment (123456).
Then, with the command
grep 123456 /proc/*/maps, I see:
/proc/3956/maps: blah blah blah 123456 /SYSV000000 (deleted) /proc/9999/maps: blah blah blah 123456 /SYSV000000 (deleted)
So there is a way to get the processes that attached to it. I'm pretty certain that the
dest status and
(deleted) indicator are because the creator has marked the segment for destruction once the final detach occurs, not that it's already been destroyed.
So, by scanning of the
/proc/*/maps "files", you should be able to discover which PIDs are currently attached to a given segment.