Unable to access Plesk after an upgrade: Upgrade stuck and login page is blank or 504 Gateway Timeout is shown

Symptoms

• Plesk is not accessible after an upgrade. One of the following error messages is shown in a browser:

  PLESK_INFO: 504 Gateway Timeout

• Plesk upgrade/update hangs on one of these stages:

  CONFIG_TEXT: ===> Plesk database scheme upgrade has been completed

  Or:

  CONFIG_TEXT: ===> Cumulative upgrade of Plesk (final stage) has been completed.

• In the output of the command "ps auxf", it is possible to find the below string or something similar that is not changing for a long time:

  CONFIG_TEXT: \\_ /usr/bin/sw-engine -c /usr/local/psa/admin/conf/php.ini /usr/local/psa/admin/plib/Upgrade/upgrade.php

• After killing this process, upgrade can be continued or it hangs again.

• It may be not possible to login to Plesk: login page is blank.

• When starting Plesk Installer, it hangs on one of these stages:

  CONFIG_TEXT: gpg-pubkey-c105b9de-4e0fd3a3 gpg(CentOS-6 Key (CentOS 6 Official Signing Key) <c
  gpg-pubkey-914bdf7e-55c05220 gpg(Plesk Team info@plesk.com)

  Or:

  CONFIG_TEXT: Ign http://autoinstall.plesk.com all/all Translation-en
  Ign http://autoinstall.plesk.com trusty/all Translation-en
  Fetched 221 kB in 3s (57.1 kB/s)
  Reading package lists...
  ERROR: Interrupted by user
  Reading package lists...

• The command "plesk repair installation" and other Plesk commands can also stuck.

Cause

This is a Plesk bug with ID PPPM-3717, which is planned to be fixed in future product updates.

Resolution

1. Connect to a Plesk server via SSH.

2. Remove temporary lock_manager files:

   # rm -f /usr/local/psa/var/cache/SharedLockManagerStorage*
   # rm -f /var/lock/parallels-panel-bootstrapper-running.lock

3. Restart the Plesk services:

   # service sw-engine restart && service sw-cp-server restart

4. Start Plesk Installer and continue the upgrade.