Restart of the networking service failed on Debian-based SolusVM KVM guests when addition IP was added: RTNETLINK answers: File exists

Symptoms 

Restart of the networking service failed on Debian-based KVM guests:

# systemctl status networking.service
...
Active: failed (Result: exit-code) since Wed 2018-10-10 15:34:48 BST; 7s ago
...
Oct 10 15:34:48 c6.ubuntu16.test ifup[740]: RTNETLINK answers: File exists
Oct 10 15:34:48 c6.ubuntu16.test ifup[740]: Failed to bring up eth0:0.
Oct 10 15:34:48 c6.ubuntu16.test systemd[1]: networking.service: Main process exited, code=exited, status=1/FAILURE
Oct 10 15:34:48 c6.ubuntu16.test systemd[1]: Failed to start Raise network interfaces.
Oct 10 15:34:48 c6.ubuntu16.test systemd[1]: networking.service: Unit entered failed state.

There is an additional IP address asigned to the virtual server and /etc/network/interfaces configuration file has extra gateway parameter

Cause

The issue caused by SolusVM bug #SVM-1091 and will be fixed in future releases

Resolution

The issue is more a cosmetic one and can be ignored. As a workaround, perform the steps below:

1. Connect to the guest virtual server via SSH
2. Open /etc/network/interfaces with a text editor and comment extra gateway parameter