SSH - Launch a terminal on your session without having to authenticate yourself

Imagine that you regularly need to connect to your Linux server: you need to launch a tool such as Putty, you need to enter your login, password, etc. and carry out various operations before you can access the terminal.

If your password isn't saved in Putty's configuration, you'll have to launch another tool like a password vault; in short, it's annoying.

In this article, we'll look at how to authenticate once and for all on the server using an SSH key.

Two articles that build on this one: How to connect to your hosting server using SSH, applied to a real hosting account, and Master your ssh command and select the host from a list once your ~/.ssh/config holds a dozen aliases.

TLDR​

Create an SSH key, copy it to the remote server and run an SSH connection. Steps 1 and 2 have to be done just once.

In-depth​

1. Creating the SSH key​

The first thing to do, only once, is to generate an SSH key on your host for the remote server.

By running ssh-keygen -t ed25519 -C "christophe@my_blog.be" -f ~/.ssh/id_ed25519_my_blog (or ssh-keygen -t rsa -C "christophe@my_blog.be" -b 4096 -f ~/.ssh/id_rsa_my_blog for the RSA algorithm):

1. You'll create an SSH key for the remote user christophe on server my_blog.be. You'll get a private key and a public one,
2. The key will be saved on your machine and the filename will be ~/.ssh/id_ed25519_my_blog for the private key (and will have the ~/.ssh/id_ed25519_my_blog.pub for the public one),
3. The key will be based on the ed25519 algorithm.

2. Copying the key​

When this is done, you've to copy the public SSH key to your remote server. To do this, please run ssh-copy-id -i ~/.ssh/id_ed25519_my_blog christophe@my_blog.be. This has to be done just once.

1. You'll copy your local SSH public key id_ed25519_my_blog on the my_blog.be server,
2. The key will be added for the remote user christophe,
3. You'll have to provide the password of that user when prompted.

3. Connect to the server​

Now, everything is in place, you can run ssh -i ~/.ssh/id_ed25519_my_blog christophe@my_blog.be and it should work because the id_ed25519_my_blog public key was already copied on the server my_blog.be for the user christophe.

Copying files from your host to the server​

Now that we can connect to the server so easily, we can f.i. copy files from our host like this:

$ scp -i ~/.ssh/id_ed25519_my_blog local_file christophe@my_blog.be:/remote_file▋

First we need to specify our local file (or folder) then where to copy it.

Copy files from the server to your host​

Now, in the other direction, from the server to your host:

$ scp -i ~/.ssh/id_ed25519_my_blog christophe@my_blog.be:/remote_file local_file▋

Copying folders​

If you need to copy a folder, just add the recursive flag i.e. -r.

For instance, scp -r christophe@my_blog.be:~/backup/ . will copy the entire ~/backup folder from the server into my current, local, folder. Really handy.

Tips​

Running ssh from Microsoft Terminal​

The SSH experience is much, much better using Microsoft Terminal than the old Putty application.

With Microsoft Terminal, you can work in a full screen mode, you can have a nice background image, you can work with a much better font (the standard one with Putty is awful), use tabs, ...

If you've already experienced Putty, you know what I mean.

Using the config file​

As we have seen, when using the ssh or scp command, we need to specify the user name, the name or IP address of the server and the name of the file containing the private key. That's a lot of information to provide, isn't it?

What's more, like me, I can't remember all this information. I just want to connect to my application server and that's it!

It would be nice to be able to ssh my_application and that's it. No? This is the purpose of the ~/.ssh/config file!

To connect on that server, my ssh command looks like this: ssh christophe@my_blog.be -i ~/.ssh/id_ed25519_my_blog. Not easy to remember!

Let's create a ~/.ssh/config file. If the file already exists, just edit it: code ~/.ssh/config.

Add these lines in the file:

Host my_app?
    Hostname my_blog.be?
    User christophe
    IdentityFile ~/.ssh/id_ed25519_my_blog?

Save the file and go back to the console.

Now, you can just run ssh my_app to make the connection. Pretty easy no?

Want more info? Continue your reading https://linuxize.com/post/using-the-ssh-config-file/

Going further​

Once your ~/.ssh/config file starts to grow with aliases, two companion articles are worth a look: SSH - Autosuggestions with ZSH, so you never have to remember an alias again, and Using sftp on the command line if you need the sftp counterpart of scp.