Plesk upgrade/update fails: Error: Failed to attach to cgroup

Symptoms

Plesk update/upgrade fails with the following error in
/var/log/plesk/install/autoinstaller3.log
file:

[2017-05-11 15:06:34.889279] Warning: Failed to attach to cgroup /sys/fs/cgroup/systemd/user/root/tasks, installer might be unexpectedly killed later by the system
 [2017-05-11 15:06:34.889510] DEBUG: web server PID: 5688
 [2017-05-11 15:06:36.892013] Error: Can't start build-in web-server
 Not all packages were installed.
 Please try to install packages again later.
 Please resolve this issue and try to install the packages again.
 If you cannot resolve the issue on your own, contact product technical support for assistance.

Cause

Not clear

Resolution

1. Login into the server via SSH;
2. Re-run upgrade/update:

   # plesk installer