*** RESOLVED ***
A full server crash after following an PLESK guide to disable IPV6 (Ubuntu 18.04.5 LTS, Plesk Obsidian 18.0.27).
Edited /etc/sysctl.conf and adding:
net.ipv6.conf.all.disable_ipv6=1
net.ipv6.conf.default.disable_ipv6=1
Applied the settings :
sysctl -p
In PLESK under Tools & Settings > IP Addresses. and clicking Reread IPs . Plesk shows Configuration under the IPv6 address and offers to Click to Fix.
Figured it was not worth messing around with, so reverted to change to the /etc/sysctl.conf and applied changes again. Then tried to Reread IPs. However instead of claiming all was dine, PLESK still claimed a configuration error… so I clicked for it to fixed -> the server crashed immediately.
All external access to the server IP is gone, also SSH access stopped working. I am able to access the console via KVM, but I have no idea what PLESK might have done. I figured something must be wrong network configuration wise in relation to my IPv6 attempted tweaks.
Help and tips greatly appreciated to get this box running again without loss of data.
Update: It seem PLESK created a file -> /etc/netplan/10-plesk.yaml -> that is causing the full system crash as it removed the IPv4 address on the network adapter. Deleting it got the server back up in case anyone else runs into something similar.