Apache is not starting and throws messages like "[emerg] (28)No space left on device: Couldn't create accept lock" in error log.

Apache can not start and shows in error log messages like this:

[emerg] (28)No space left on device: \
    Couldn't create accept lock \
    (/var/log/httpd/accept.lock.24765) (5)

but the partition is not full, it’s not a quota problem and yes – the partition is writable. So where is the problem?

Solution

List semaphore arrays owned by user apache:

ipcs -s | grep apache

Cleanup stuck semaphores:

ipcs -s \
    | grep apache \
    | perl -e 'while (<STDIN>) { @a=split(/\s+/); print `ipcrm sem $a[1]`}'

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

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

Now restart Apache. Problem solved?