Unable to access Plesk: /usr/local/psa/admin/logs/panel.log cannot be opened with mode “a”

Symptoms

In an attempt to access Plesk, the process fails with the error below: 

ERROR: Zend_Log_Exception
"/usr/local/psa/admin/logs/panel.log" cannot be opened with mode "a"

Cause

Wrong ownerships for the /var/log/plesk/ directory or /var/log/plesk/panel.log file.

Resolution

1. Log into the the server via SSH.

2. Execute the commands below one by one to set proper ownerships for /var/log/plesk/ directory:

   # chmod 0750/var/log/plesk/

   # chown psaadm:root /var/log/plesk/

3. Run the following commands to set correct ownerships for the /var/log/plesk/panel.log file:

   # chmod 0640 /var/log/plesk/panel.log

   # chown psaadm:root /var/log/plesk/panel.log