Apache accept lock fix

From Webpipe Wiki

Fixing Apache "No space left on device: Couldn't create accept lock" errors

Error Message: When starting Apache, I get this error message in the main Apache error_log:

[emerg] (28)No space left on device: Couldn't create accept lock
[notice] suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)
[notice] Digest: generating secret for digest authentication ...
[notice] Digest: done
[warn] pid file /etc/httpd/run/httpd.pid overwritten -- Unclean shutdown of previous Apache run?
[emerg] (28)No space left on device: Couldn't create accept lock

First off, check to make sure that you really aren't out of disk space, or have hit a quota limit. Another way that Apache can create the "accept lock" is with a semaphore. A semaphore is an inter-process communication tool that is used by Apache to communicate with it's child processes. This error message may mean that Apache couldn't create a new semaphore.

Check to see how many semaphores are currently in use. If Apache is running correctly, you should see something like this:

# ipcs -s
------ Semaphore Arrays --------
key semid owner perms nsems
0x00000000 68681743 apache 600 1
0x00000000 68714515 apache 600 1
0x00000000 68747291 apache 600 1

If Apache is stopped, and you still see these semaphores, then you can safely kill them by running this command for each semaphore id (in the second column)

$ ipcrm -s <semid> 

To destroy all semaphores, you can run this from the command line (with "apache" being the apache-user):

for semid in `ipcs -s | grep apachec | cut -f2 -d" "`; do ipcrm -s $semid; done

If you are out of semaphores

If you can't create any more semaphores:

Sometimes your system may need to increase the number of semaphores that are available on the system. This requires a change to a kernel parameter. If you are running on a virtual server and cannot modify kernel parameters, you may need to ask your hosting provider to change this parameter on their host server To view the current parameters:

# ipcs -l
------ Shared Memory Limits --------
max number of segments = 4096
max seg size (kbytes) = 32768
max total shared memory (kbytes) = 8388608
min seg size (bytes) = 1

------ Semaphore Limits --------
max number of arrays = 1024
max semaphores per array = 250
max semaphores system wide = 256000
max ops per semop call = 32
semaphore max value = 32767

------ Messages: Limits --------
max queues system wide = 1024
max size of message (bytes) = 8192
default max size of queue (bytes) = 16384

To change these parameters, modify the file /etc/sysctl.conf and add the following lines:

kernel.msgmni = 1024
kernel.sem = 250 256000 32 1024

Then load these settings with the command:

sysctl -p

Your Apache process should now be able to create the needed semaphores and run properly.