Unable to install system updates or update Plesk: Another app is currently holding the yum lock

Symptoms

• Unable to install system updates from Plesk at Tools & Settings > System Updates:

  Another app is currently holding the yum lock

• Unable to update Plesk at Tools & Settings > Updates, one of the following errors might be shown:

  Error: Unable to start Plesk Installer. The following error has occurred: Installation could not be started: another installation procedure is currently running.

  System package manager is already running.
  ERROR: Exited with returncode 100.

Cause

Yum process is stuck.

Resolution

1. Connect to the server via SSH.

2. Kill the stuck processes locking the Yum package manager:

   # for PID in `ps awufx | egrep yum|pum|install|rhn_check | grep -v grep | awk '{print $2}'`; do kill -9 $PID; done