Plesk installation or update fails: ERROR while trying to check the hostname

Symptoms

Plesk installation or update fails with the following error message:

...
 Trying to resolve hostname ‘localhost.localdomain’ and validate its IP address…
 Unable to resolve host name.
 Please specify the host name in the /etc/hosts file or specify DNS configuration in the /etc/resolv.conf on your system.
 ERROR while trying to check the hostname
 ....

Cause

Misconfiguration of the /etc/hosts file or invalid PTR record.

Resolution

1. Connect to the server via SSH

2. Back up the current
/etc/hosts
file:

   # cp -a /etc/hosts{,.backup}

3. Edit the /etc/hosts file as follows:

   Note: The second line starting with ::1 should be added only if the system has IPv6. This can be verified with the following command: ip -6 a

   127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
    ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
    203.0.113.2 plesk.example.com host

   Where:

   – 203.0.113.2 is the main IP address
   – plesk.example.com is the hostname: How to change or get the server hostname on Plesk server

4. Make sure that the main IP address has a valid PTR record resolving to a valid FQDN hostname:

   # dig +short -x 203.0.113.2
   plesk.example.com.