Two dead shared memory segments upon reboot in 11i

[Hiro Asari]

On all 11i boxes that I've checked so far (about 10 of them), there are always 2 dead shared memory segments with key 0. One is owned by root, and the other by www. Could someone explain to me what's going on there?

m 1808 0x00000000 D-rw------- root root 6 1052672
m 2209 0x00000000 D-rw------- www other 6 184324


The dead shared memory segments don't exist on 11.0 (as far as I can tell).

[Andy Beal]

The one owned by www is probably apache running. I have some similar segments showing my my boxes, you can do an ipcs -mp to display the pid associated with each segment.

Andy

[Bill Hassell]

The most usefu options for ipcs are:

ipcs -bmop

That should show you all the details.

[James Murtagh · Accepted solution]

Hi Hiro,

Shared memory segments remaining even if no processes are currently accessing them is a feature of the SysV implementation, this is normal. This is, of course, dependant of the implementation, but I know the processes in question and this is desired. You can use the shminfo utility to see what processes created and last accessed them, its available here:

ftp://contrib:9unsupp8@hprc.external.hp.com/sysadmin/programs/shminfo

Cheers,

James.

[James Murtagh]

My apologies, I misread the question. This key is the IPC_PRIVATE key (see "man shmget") used by processes that only require the process that created it and its child processes to access. Again, perfectly normal.

[Elena Leontieva]

On my server I also have shared memory segments with 0 key and PID is associated with apache. From man ipsc, the D mode means that
"the associated shared memory segment has been removed. It will disappear when the last process attached to the segment detaches it."

Elena.