topic Re: Shared memory and ipcs in Operating System - HP-UX

Shared memory and ipcs

Roberto Volsa — Fri, 04 Apr 2003 14:11:40 GMT

Hello,
on ipcs output i read:
Shared Memory:
m 2055 0x00000000 D-rw------- root root
m 13320 0x00000000 D-rw------- www other

What does it mean that "D". We released earlier another shared memory allocated to an user of an application shutted down.

Thanks in advance

Re: Shared memory and ipcs

Pete Randall — Fri, 04 Apr 2003 14:13:52 GMT

I believe the D indicates it's been removed. Here's a quote from the man page:

"MODE The facility access modes and flags: The mode consists
of 11 characters that are interpreted as follows:

The first two characters can be:

R A process is waiting on a msgrcv().
S A process is waiting on a msgsnd().
D The associated shared memory segment has been
removed. It will disappear when the last
process attached to the segment detaches it."

Pete

Re: Shared memory and ipcs

Sridhar Bhaskarla — Fri, 04 Apr 2003 14:15:57 GMT

Hi,

D indicates that it is marked for deletion. Once the processes accessing it are detached, then the segment will go away. YOu can often see this behaviour with softwares like MQ that make use of shared memory segments heavily.

-Sri

Re: Shared memory and ipcs

Roberto Volsa — Fri, 04 Apr 2003 14:16:48 GMT

Thanks for your kind explanation.
The two shared memory segmentas are allocatet to www user (i don't care of) and root user. How to understand if there is some impact for that shared memory used by root and Detached?