Module SSL requires /run/apache_ssl_mutex to exist at startup but it does not. This is configured in /etc/apache2/modules.d/40_mod_ssl.conf. --------------------- ... ## Semaphore: # Configure the path to the mutual exclusion semaphore the SSL engine uses # internally for inter-process synchronization. Mutex file:/run/apache_ssl_mutex ssl-cache ... --------------------- Workaround: Use /etc/tmpfiles.d/apache.conf to create missing directory at boot: --------------------- d /run/apache_ssl_mutex 0755 root root ---------------------