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One of the more interesting components is network-console. It allows you to do a large part of the installation over the network via SSH. The use of the network implies you will have to perform the first steps of the installation from the console, at least to the point of setting up the networking. (Although you can automate that part with Section 4.4.)
This component is not loaded into the main installation menu by default, so you have to explicitly ask for it. If you are installing from CD, you need to boot with medium priority or otherwise invoke the main installation menu and choose Load installer components from CD and from the list of additional components select network-console: Continue installation remotely using SSH. Suc- cessful load is indicated by a new menu entry called Continue installation remotely using SSH.
10. That is: press the Alt key on the left-hand side of the space bar and the F2 function key at the same time.
After selecting this new entry, you will be asked for a temporary password to be used for connecting to the installation system and for its confirmation. That’s all. Now you should see a screen which instructs you to login remotely as the user installer with the password you just provided. Another important detail to notice on this screen is the fingerprint of this system. You need to transfer the fingerprint securely to the person who will continue the installation remotely.
Should you decide to continue with the installation locally, you can always press Enter, which will bring you back to the main menu, where you can select another component.
Now let’s switch to the other side of the wire. As a prerequisite, you need to configure your terminal for UTF-8 encoding, because that is what the installation system uses. If you do not, remote instal- lation will be still possible, but you may encounter strange display artefacts like destroyed dialog borders or unreadable non-ascii characters. Establishing a connection with the installation system is as simple as typing:
$ ssh -l installer install_host
Where install_host is either the name or IP address of the computer being installed. Before the actual login the fingerprint of the remote system will be displayed and you will have to confirm that it is correct.
Note: The ssh server in the installer uses a default configuration that does not send keep-alive packets. In principle, a connection to the system being installed should be kept open indefinitely. However, in some situations — depending on your local network setup — the connection may be lost after some period of inactivity. One common case where this can happen is when there is some form of Network Address Translation (NAT) somewhere between the client and the system being installed. Depending on at which point of the installation the connection was lost, you may or may not be able to resume the installation after reconnecting.
You may be able to avoid the connection being dropped by adding the option
-o ServerAliveInterval=value when starting the ssh connection, or by adding that option in your ssh configuration file. Note however that in some cases adding this option may also cause a connection to be dropped (for example if keep-alive packets are sent during a brief network outage, from which ssh would otherwise have recovered), so it should only be used when needed.
Note: If you install several computers in turn and they happen to have the same IP address or hostname, ssh will refuse to connect to such host. The reason is that it will have different fingerprint, which is usually a sign of a spoofing attack. If you are sure this is not the case, you will need to delete the relevant line from ~/.ssh/known_hosts 11 and try again.
After the login you will be presented with an initial screen where you have two possibilities called Start menu and Start shell. The former brings you to the main installer menu, where you can continue with the installation as usual. The latter starts a shell from which you can examine and possibly fix the remote system. You should only start one SSH session for the installation menu, but may start multiple sessions for shells.
11. The following command will remove an existing entry for a host: ssh-keygen -R <hostname|IP address>.
Warning
After you have started the installation remotely over SSH, you should not go back to the installation session running on the local console. Doing so may corrupt the database that holds the configuration of the new system. This in turn may result in a failed installation or problems with the installed system.