Apache: No space left on device: Couldn’t create accept lock

Apache went down without a problem, but it refused to start properly, and didn’t bind to any ports. Within the Apache error logs, this message appeared over and over:

[emerg] (28)No space left on device: Couldn't create accept lock

 If this happens to you, check these items in order:

1. Check your disk space.

2. Review filesystem quotas

3. Clear out your active semaphores

Semaphores are used for communicating between the active processes of a certain application. In the case of Apache, they’re used to communicate between the parent and child processes. If Apache can’t write these things down, then it can’t communicate properly with all of the processes it starts.

Run this command as root:

# ipcs -s

If you see a list of semaphores, Apache has not cleaned up after itself, and some semaphores are stuck. Clear them out with this command:

# for i in `ipcs -s | awk '/httpd/ {print $2}'`; do (ipcrm -s $i); done

Now, in almost all cases, Apache should start properly. If it doesn’t, you may just be completely out of available semaphores. You may want to increase your available semaphores, and you’ll need to tickle your kernel to do so. Add this to /etc/sysctl.conf:

kernel.msgmni = 1024

kernel.sem = 250 256000 32 1024

And then run sysctl -p to pick up the new changes.