Perl script to allocate shared memory (and annoy sysadmins)

Dave — Mon, 02 Nov 2009 01:54:00 +0000

I once ran into an instance where the Unix admins didn’t believe me that i was running out of shared memory despite the errors, I was showing them. I wrote this perl script to allocate chunks of shared memory until it failed to prove to them that yes, regardless of what you have the global ulimits set to my user’s limits were lower.

#!/usr/bin/perl -w

use IPC::SysV qw(IPC_PRIVATE IPC_RMID S_IRWXU);

#$size = 314580992;
$size = 50000000;
$id = shmget(IPC_PRIVATE, $size, S_IRWXU) || die "$!";
sleep 10;
shmctl($id, IPC_RMID, 0)

HowTo Find info about Shared memory allocation

Dave — Mon, 02 Nov 2009 01:48:05 +0000

Sometimes you may see core dumps, etc related to lack of shared memory.
To check to see how much is currently being used you can use the below command:

kerrd@vexbert<10> ipcs -bm
IPC status from  as of Thu Oct 30 10:42:06 PDT 2008
T         ID      KEY        MODE        OWNER    GROUP      SEGSZ
Shared Memory:
m 1493172237   0x32d14fb8 --rw-r-----   oracle      dba 2097160192
m 1979711547   0x5e000b64 --rw-------     root     root        512
m  721420366   0xe867eba0 --rw-r-----   oracle      dba 2147491840
m         25   0x67e97344 --rw-r-----   oracle      dba  419438592
m         21   0xc4986724 --rw-rw----   oracle      dba  629153792
m         19   0x71e930c0 --rw-rw----   oracle      dba 1073758208
m          7   0x4154520e --rw-rw-rw-     root   tivoli    1048576
m          6   0x4154520a --rw-rw-rw-   tivoli   tivoli    1048576
m          5   0x4154520d --rw-rw-rw-   tivoli   tivoli    1048576
m          4   0x4154520c --rw-rw-rw-   tivoli   tivoli    1048576
m          3   0x4154520f --rw-rw-rw-   tivoli   tivoli    1048576
m          2   0x4154520b --rw-rw-rw-   tivoli   tivoli     524288
m          1   0x41545200 --rw-rw-rw-   tivoli   tivoli    1048576
m          0   0          --rw-------     root     root         64

The Oracle/DBA segments are related to Oracle database instances.
The SEGSZ is limited by the Unix kernel.

david kerr » unix

Perl script to allocate shared memory (and annoy sysadmins)

HowTo Find info about Shared memory allocation