SSH config

The SSH configuration file resides in the .ssh directory in your home directory (at least when using Linux or MacOS X). It is simply called config. It is not created by default, so you would have to create the initial version. Make sure only the owner has read and write permission, neither group nor world should be able to read the file.

To simplify login in to a host, say login.hpc.kuleuven.be as user vsc50005, you can add the following:

Host *
    ServerAliveInterval 60

Host hpc
    HostName login.hpc.kuleuven.be
    User vsc50005
    ForwardAgent yes
    ForwardX11 yes

Here, you should replace login.hpc.kuleuven.be by the hostname of the remote host you want to login to, and vsc50005 by your user name on that system.

Now you can log in simply using

$ ssh hpc

Multiple keys

If you have multiple SSH key pairs to authenticate to various servers (which is good practice), it is prudent to add a specific identity file to authenticate to a specific server.

Host * ServerAliveInterval 60

Host hpc HostName login.hpc.kuleuven.be User vsc50005 ForwardAgent yes ForwardX11 yes IdentityFile ~/.ssh/id_rsa_vsc50005

Here, `~/.ssh/id_rsa_vsc50005` is the private key for the host
`login.hpc.kuleuven.be`.  It is good practice to add this in case you have
multiple private keys added to an SSH agent.


## Junp hosts

To use a host as a proxy, but log in through it on another node, the
following entry can be added:

Host leibniz Hostname login.leibniz.antwerpen.vsc User vsc50005 ProxyJump hpc ForwardAgent yes ForwardX11 yes

In this example, `login.leibniz.antwerpen.vsc` is the host you actually
want to log in to, and `login.hpc.kuleuven.be` is the host you are using
as a proxy jump hosts.


## Avoiding unwieldy config files

If you access many hosts, your `.ssh/config` file can grow very long.  In that
case, it might be convenient to group hosts into distinct files, and include
those into your main `.ssh/config` file, e.g.,

Include ~/.ssh/config_vsc ```