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====== SSH ======

====== Linux ======

On Linux you can generate an SSH key file with ssh-keygen, e.g.

    ssh-keygen -f ~/.ssh/id_fuberlin -t ed25519 -C "yourusername-$HOSTNAME-$(date +%Y%m%d)"

would generate key files ''~/.ssh/id_fuberlin'' and ''~/.ssh/id_fuberlin.pub'' of type
ed25519, preferable for it's strong yet short and therefore easy to handle keys,
with a comment of ''yourusername-yourhostname-20230414'', which makes it easier to
tell different keys apart. You can also name the files differently, but the
prefix ''id_'' and the location in ''~/.ssh'' are customary.

The content of the public key file (with extension ''.pub,'' e.g. ''id_fuberlin.pub'' in
our example) needs to be added to ''~/.ssh/authorized_keys''.

When doing this from outside the department (with a previous key id_fuberlin already
installed), this can be done easily with the ssh-copy-id tool:

    ssh-copy-id -i ~/.ssh/id_fuberlin yourusername@login.physik.fu-berlin.de

To use an SSH key you can either pass it to ssh with the ''-i'' option, configure it
in your ''~/.ssh/config'' or, most easily, load it into your running SSH agent

    ssh-add ~/.ssh/id_fuberlin

You might need to start the agent first, if it has not been started by your
Desktop environment already, e.g. via

    systemctl --user enable --now ssh-agent.socket

on Debian and Ubuntu, which will also ensure, that it is started on subsequent
logins or by running

    eval $(ssh-agent)

in a shell.

<note tip>All department Linux desktops start an SSH agent by default (Since 06.03.2026, please logout and login again if you get an error message)</note>

If you use alternative SSH clients or clients that use SSH under the hood, like
X2Go, you will have to configure them to use your key file.

Please use different keys for different purposes, e.g. for general SSH usage at
the department, generate a different key than you use for our GitLab.

====== Windows ======

On Windows you can [[https://winscp.net/eng/docs/ui_puttygen|use PuTTYgen to generate key files]]. You can [[https://winscp.net/eng/docs/ui_login_authentication|use these with WinSCP]] to connect to storage systems like grouphome and storage.

====== Mac OSX ======

On Mac OSX you can follow the Linux description on the usage of ''ssh-keygen''. An SSH agent is provided by your system.