I recently ran into the following problem on an Apache 2.4 server, where after server reboot the service itself would no longer start.
This was the error whenever I tried to start it:
$ tail -f error.log [auth_digest:error] [pid 11716] (2)No such file or directory: AH01762: Failed to create shared memory segment on file /run/httpd/authdigest_shm.11716 [auth_digest:error] [pid 11716] (2)No such file or directory: AH01760: failed to initialize shm - all nonce-count checking, one-time nonces, and MD5-sess algorithm disabled
Systemd reported the same problem;
$ systemctl status -l httpd.service - httpd.service - The Apache HTTP Server Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled; vendor preset: disabled) Active: failed (Result: exit-code) since ...
The cause is shown in the first error message: Failed to create shared memory segment on file /run/httpd/authdigest_shm.11716.
If I traced this, I noticed the directory /run/httpd no longer existed. The simple fix in this case, was to re-create that missing directory.
$ mkdir /run/httpd $ chown root:httpd /run/httpd $ chmod 0710 /run/httpd
The directory should be owned by root and writeable for the root user. The Apache group (in my case, httpd), needs executable rights to look into the directory.