Apache: Fatal Error Unable to create lock file: Bad file descriptor (9)

Symptoms

A site that is not functioning or opening properly gives either a 503 Service Unavailable or 500 Internal Server Error, and the following error in the Apache error log ( /var/log/apache2/error_log ) and/or the stderr.log ( /var/log/apache2/stderr.log ):

[:error] [pid 11817] [client 0.0.0.0:52413] Fatal Error Unable to create lock file: Bad file descriptor (9)

Description 

The "Fatal Error Unable to create lock file: Bad file descriptor (9)" error is typically caused by issues with /tmp or CageFS. 

Workaround

First, ensure /tmp has the correct permissions assigned to it. You can do so by running the following command:

stat -c %a /tmp

If /tmp does not have 1777 permissions, this can be corrected with the following command:

chmod -v 1777 /tmp /var/tmp

If you have CageFS enabled, you may need to disable and re-enable CageFS for the user by running the following commands:

/usr/sbin/cagefsctl --disable USERNAME

/usr/sbin/cagefsctl --enable USERNAME

Please note, make sure to replace USERNAME with the actual username. 

Additional Resources

CloudLinux Docs - Command-line tools (CLI) - CageFS