techblog 

We recently had an issue whereby one of our apache servers crashed failing to clean up a shared memory segment. We were using shared memory for SSL session caching:

SSLSessionCache         shm:/var/log/httpd2/gcache(512000)

Which uses a shared memory segment:

-bash-2.05b$ sudo ipcs -a
Password:
IPC status from  as of Tue Mar 25 16:26:29 GMT 2008
T ID KEY MODE OWNER GROUP CREATOR CGROUP CBYTES QNUM QBYTES LSPID LRPID STIME  RTIME CTIME
Message Queues:
T ID KEY MODE OWNER GROUP CREATOR CGROUP NATTCH SEGSZ CPID LPID ATIME DTIME CTIME
Shared Memory:
m 2304 0x13022 --rw------- root other root other 32 512000 17975 9314 9:01:41 9:26:26 9:01:41
T    ID  KEY  MODE OWNER GROUP CREATOR CGROUP NSEMS OTIME  CTIME
Semaphores:
s 65536 0x1cbd       --ra-------     root     root     root     root   129 no-entry 13:47:45
s       1  0x1001cbd  --ra-------     root     root     root     root   128 no-entry 13:47:45

After Apache had crashed when we attempted a startup we received the following errors:

 Tue Mar 25 08:43:48 2008] [error] Cannot allocate shared memory: (17)File exists 

It was a pretty straightforward fix, all we had to do was the following (as root):

ipcrm -m 2304 

This removes the shared memory segment and Apache could be started quite happily once again.