No space left on device: Cannot create SSLMutex

This error indicates that the server has run out of available slots for "inter-process communication". This can occur when a process crashes before cleaning up after itself.

The ipcs command will list semaphores and shared memory slots in use. If there is a large number of entries in use by the apache user use ipcrm to remove them.

Then, check your server's error log (possibly with LogLevel debug set) to figure out why it's crashing, or see: /dev/debugging.html