Unable to start apache " pid file /usr/local/apache/logs/httpd.pid overwritten — Unclean shutdown of previous Apache run? semget: No space left on device"

If you are unable to start apache and you are getting the error log as

[Sat Oct 10 00:11:01 2008] [warn] pid file /usr/local/apache/logs/httpd.pid overwritten — Unclean shutdown of previous Apache run?
semget: No space left on device

 
It means There is no more space left in Semaphore Arrays for Apache.
semaphore is a location in memory whose value can be tested and set by more than one process.
you can check the semaphore arrays on your server using the following command

ipcs -s

It results

------ Semaphore Arrays --------
key semid owner perms nsems
0x00000000 360448 nobody 600 1
0x00000000 393217 nobody 600 1
0x00000000 425986 nobody 600 1
0x00000000 458755 nobody 600 1
0x00000000 524292 nobody 600 1
0x00000000 1114117 nobody 600 1
0x00000000 1441798 nobody 600 1
0x00000000 3604487 nobody 600 1
0x00000000 3702792 nobody 600 1
0x00000000 3768329 nobody 600 1
0x00000000 6422538 nobody 600 1
0x00000000 7077899 nobody 600 1

If here you get big list of semaphores it means some semaphores are stuck. You can clear them out with this command:

for i in `ipcs -s | awk '/nobody/ {print $2}'`; do (ipcrm -s $i); done

 Restart apache
#/etc/init.d/httpd restart