[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

But wait, you have space? Apache went down unexpectedly and left some extra semaphore-arrays owned by the apache user nobody. so:

ipcs -s | grep nobody

And the following should fix the problemo:

ipcs -s | grep nobody | perl -e 'while () { @a=split(/\s+/); print `ipcrm sem $a[1]`}'