I used remote access to upgrade my Ubuntu server. After the upgrade I could not connect over Ethernet. ( I could not access over Wi-Fi, but that was a different problem).
If I pinged from either end, it did not connect.
On my server, the network server for the network connection wired, did not have a MAC address specified. I used the pull down and selected it. I do not know if this is relevant.
My laptop had address 10.1.0.2, and the server had address 10.10.0.3.
On the server the command
ip addr
gave
2: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 ...
inet 10.1.0.3/24 brd 10.1.0.255 scope global noprefixroute eno1
I used the command
sudo ip route add 10.1.0.2 dev eno1
to define the route, and connectivity was temporarily restored. I could ping from either machine.
Digging deeper
The command
grep -i warn /var/log/syslog
gave
NetworkManager[1457]: <warn> [...] keyfile: load: "/etc/NetworkManager/system-connections/eno1": failed to load connection: File permissions (100604) are insecure
ls -ltr /etc/NetworkManager/system-connections/eno1
gave
-rw----r-- 1 root root 376 Oct 21 2022 /etc/NetworkManager/system-connections/eno1
Where file permission xxx604 is -rw—-r–, which allows “other” to read the file
The command
sudo chmod o-r /etc/NetworkManager/system-connections/*
removes the “other” read permission.The next reboot gave me connectivity back.
Lessons learned
After doing an upgraded, (or perhaps once a week) display the syslog for warn and error and resolve any problems.
ColinPaice 