.. _linux_ssh:

Remote Access via SSH (to the IMADA Computer Lab)
=================================================

The "``ssh``" (Secure Shell) program makes it possible to make encrypted connections to other (Linux) computers.
The basic usage is to get command line access on remote machines (for example in the :ref:`IMADA Computer Lab <imada-comp-lab>`),
but it can do much more, like facilitating file transfers through the "``scp``"
and "``rsync``" commands, and proxying network traffic through other computers.

- `How Secure Shell Works (SSH) <https://www.youtube.com/watch?v=ORcvSkgdA58>`__, Computerphile on Youtube.

The basic command is::

    ssh username@hostname

The IMADA Computer Lab machines are not accessible directly from the internet, so you will either need to be physically on SDU
on the eduroam network, or enable the `SDU VPN <https://any.sdu.dk>`__.
Once on the right network, you can connect to one of the lab machines.
They each have a name on the form "``imadaX.stud-srv.sdu.dk``"
where "``X``" is a number between 0 and 3. For example::

    ssh myUsername@imada3.stud-srv.sdu.dk

If you use the machines often, it can be bothersome to type this all the time, so we can make an SSH configuration file which simplifies it.
If the folder "``~/.ssh``" does not exist, create it. Then create/open the file "``~/.ssh/config``",
and fill in something similar to the following::

    Host imada0
        User myUsername
        HostName imada0.stud-srv.sdu.dk
    Host imada1
        User myUsername
        HostName imada1.stud-srv.sdu.dk
    Host imada2
        User myUsername
        HostName imada2.stud-srv.sdu.dk
    Host imada3
        User myUsername
        HostName imada3.stud-srv.sdu.dk

To connect to machine 3 you can now use "``ssh imada3``".

Further, by generating and copying keys, it is possible to avoid having to type your password,
see :ref:`imada-ssh-key`.

See :ref:`imada-comp-lab` for more information on the IMADA Computer Lab.