I have two computers I use regularly which have two (or with a Vodem, three) network adapters. The reason for this is at present I have two different internet connections I use regularly. One is unlimited data but has certain restrictions on it, the second is unrestricted but has a data cap. I hope to soon move to a single unrestricted connection but that is very dependent on progress with Vodafone who have so far caused four months of delays in getting connected.
One of the computers has LXQt on top of Debian, the other has KDE. Both are set up to use manually specified adapter settings in the /etc/network/interfaces file. This has continued to be the case when reinstalled and somehow in the past the user profile settings controlling this must have been set up because it keeps working with each reinstallation.
A typical entry in the file will look something like
iface enp1s0 inet dhcp
if you are using DHCP to set up the connection.
For a static configuration the entry will look like this:
iface enp1s0 inet static
Whilst I am unaware of exactly what all these parameters mean, this is what is working for me on these computers. enp1s0 is the system generated name for the network adapter. This can however be renamed with an entry like
which is placed at the top of a set of entries for an interface.
The rest is pretty self explanatory hopefully. If you have a second network adapter as in my case, another group of entries in the file can set that up as well.
Most desktop environments in Linux have a network manager GUI that is for people who want their network connections to be set up automatically and use the GUI to change settings. For example, LXQt on Debian uses connmgr and KDE on Debian uses networkmanager. These tools will need to be uninstalled as they generally override or supersede the manual settings described above.
After editing and saving the interfaces file, issue this command to reload the networking configuration:
systemctl restart networking
However this is apparently being deprecated and instead you should use the commands ifdown and ifup e.g.
Then type in ip addr to check the settings and maybe a ping, traceroute or two to ensure the default gateway is correct. Google provides a couple of servers that can be tested against, these are 184.108.40.206 and 220.127.116.11
The man page for interfaces gives more information on how to set the network interfaces up.