Symptoms
Attempting to use the cPanel provided scripts to restart services results in either the script hanging up, timing out simply failing to provide any meaningful output.
Example:
# /scripts/restartsrv_mysql --status
Use of uninitialized value in string eq at /usr/local/cpanel/Cpanel/RestartSrv/Systemd.pm line 138.
Additionally, attempting to use Systemd to restart the services results in the action failing with a similar message as this:
# systemctl status tailwatchd
Failed to get properties: Failed to activate service 'org.freedesktop.systemd1': timed out
# systemctl
Failed to list units: Failed to activate service 'org.freedesktop.systemd1': timed out
Description
The problem experienced is a result of Systemd & the Dbus service encountering a deadlock in which these services can't interact with one another and thus prevent Systemd from being able to interact with other services in the system.
Since the problem originates from a component of the Operating System (Systemd & DBUS), the failure of these services prevents the cPanel scripts from interacting with any system services.
This has been documented extensively and a few defect reports have been filed with Systemd & Dbus maintainers to prevent these services from failing in this manner.
However, due to the nature of CentOS releases, the patches are not available directly from CentOS's repositories so most servers will still be susceptible to this.
Workaround
The most known and reliable workaround for this is simply to restart your server.