In the process of upgrading to the latest Ubuntu 18 build, I am now stuck working in recovery terminal mode trying to reinstall GDM3 and ubuntu-desktop. problem is I can ping outside IP addresses, but cannot resolve names (ie. when running apt-get install it will not resolve us.archives.ubuntu.com) I have input 3 dns nameservers in my Wired Connection 1 file in NetworkManager. Rebooted and still cannot resolve names. THoughts?
This helped me in a similar situation.
As Official Ubuntu Documentation says:
If you require DNS for your temporary network configuration, you can add DNS server IP addresses in the file /etc/resolv.conf. In general, editing /etc/resolv.conf directly is not recommanded, but this is a temporary and non-persistent configuration.
This will only work for this session, and you can reinstall GDM3 and ubuntu-desktop. The file will be overwritten on reboot. So check the DNS settings after reboot in graphic mode.
On a terminal:
If no DNS in there try:
echo "nameserver 184.108.40.206" | sudo tee /etc/resolv.conf
This worked for me in a situation like this.
If you want changes to persist see this.