Apache has memory leak, you may encounter this when running apache for some time –
[emerg] (28)No space left on device: Couldn’t create accept lock
or
[crit] (28)No space left on device: mod_rewrite: could not create rewrite_log_lock Configuration Failed
or
[Wed Aug 14 00:00:09 2012] [error] (28)No space left on device: Cannot create SSLMutex

There are definitely enough space on hard disk.

Solution:
on sh system –

ipcs -s | grep apache | awk ' { print $2 } ' | xargs ipcrm sem

Or 

ipcs -s | grep apache | sudo perl -alne 'qx(ipcrm -s $F[1])'