Diagnosis

When Apache does not start and shows the following result while prompting it to start, check the error_log file,

Starting httpd : [Failed]

The following error in error_log file may be causing the issue ( /var/log/httpd/error_log )

[error] (28)No space left on device: Cannot create SSLMutex

Cause

These errors mean that there are no available IPC (inter-process communication) resources in the system, such as semaphores or shared memory segments.

To check the allocated semaphores use the command ipcs -us

Solution

Option 1:

Run this command as root,

# ipcs | grep apache

If you see a list of semaphores, apache has not cleaned itself. Use the following command to clean it,

# ipcs -s | grep apache | awk ’ { print $2 } ’ | xargs -n 1 ipcrm -s

Option 2:

Increase the limits in /etc/sysctl.conf

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

Load the new sysctl settings from  /etc/sysctl.conf

# sysctl -p