A License check appears to already be running - Systemd sessions

Symptoms

You will receive the following error when running a license check.

# /usr/local/cpanel/cpkeyclt
Updating cPanel license...Done. Update Failed!
Error message:
    A License check appears to already be running.

Description 

This may be due to the Systemd bug reported here. If so, you will see that inodes are exhausted on /run. You can check this with the command below. It will show 100% if this bug is affecting you.

# df -i /run/
Filesystem Inodes  IUsed IFree IUse% Mounted on
tmpfs      458752 458752     0  100% /run

If this shows 100%, you can verify further with the command below which will show an inode usage similar to the above.

# du --inodes --max-depth=0 /run/systemd/system/
407322 /run/systemd/system/

Workaround

You can reboot the server to clear the systemd session files.

How do I reboot my server?