Unable to install Plesk updates on Ubuntu: E: dpkg was interrupted, you must manually run 'dpkg --configure -a' to correct the problem

Symptoms

Unable to install Plesk updates on Ubuntu 14.04 or Ubuntu 16.04. The following error is displayed in the Plesk interface:

PLESK_ERROR: E: dpkg was interrupted, you must manually run 'dpkg --configure -a' to correct the problem.

The following explanation can be found in /var/log/plesk/systemupdatestool.log

# cat /var/log/plesk/systemupdatestool.log | tail -n3
2017-04-02 06:22:15 INFO: pum is called with arguments: ['--list', '--repo-info', '--json']
2017-04-02 06:22:15 ERROR: Previous Plesk installer call finished unsuccessfully. PUM will not perform any update operations until Plesk installation is fixed.
2017-04-02 06:22:15 ERROR: Exited with returncode 50.

dpkg --configure -a command hangs at restarting AppArmor and after that server reboot is required:

CONFIG_TEXT: Setting up apparmor (2.10.95-0ubuntu2.6) ...
update-rc.d: warning: start and stop actions are no longer supported; falling back to defaults

Cause

Bug in the Ubuntu kernel - #1579135: AppArmor profile reloading causes an intermittent kernel BUG

Resolution

Warning: We strongly recommend to backup the whole server before applying the steps below. If your Plesk is running inside a virtual container, contact your service provider to create a backup and in order to verify if the kernel version is supported.

1. Log in to the server via SSH.
2. Temporarily remove AppArmor post-install scripts in order to prevent AppArmor from reloading:

   # mv /var/lib/dpkg/info/apparmor.postinst ~/
   # mv /var/lib/dpkg/info/apparmor-profiles.postinst ~/

3. Disable AppArmor:

   # service apparmor stop
   # service apparmor teardown
   # update-rc.d -f apparmor remove

4. Run dpkg --configure -a to fix the initial error:

   # dpkg --configure -a

5. Upgrade Ubuntu kernel to version 4.4.0-38.57 or newer and reboot the server. For example, for version 4.4.0-72:

   # apt update
   # apt install linux-image-4.4.0-72-generic
   # sudo reboot

6. Move back AppArmor post-install scripts and reconfigure apparmor-profiles package:

   # mv ~/apparmor.postinst /var/lib/dpkg/info/
   # mv ~/apparmor-profiles.postinst /var/lib/dpkg/info/
   # dpkg-reconfigure apparmor
   # dpkg-reconfigure apparmor-profiles

7. Start AppArmor:

   # service apparmor start