Shared memory and ipcs

[Roberto Volsa]

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

[Pete Randall]

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

[Sridhar Bhaskarla]

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

[Roberto Volsa]

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?