Insane stuff you can do with ssh

If there’s a God, I think he’d probably very dissapointed with us, we have created many awful things that can’t be name because of respect. If I were God I would be dissapointed with my creation and probably would end it. But in 2002, a proof that God exists and love us appeared, the first version of OpenSSH was released.

OpenSSH is a marvellous software, it is one of the most useful things I’ve seen in my entire life, and when you master it, all of your problems will disappear.

Forwarding ports

This is a known one but that doesn’t make it less of a godsend. You can forward ports through ssh, like you have in a remote server a software running in port 4040. And because of another reasons (i.e. firewall, bound only to loopback) you want to have that port in your computer.

This is possible thanks to the -R and -L ssh flags. The syntax for both -R and -L are the same but the concept is different.

  • -L “brings” a remote port to your device.
  • -R “brings” a local port to a remote server.

So, to answer the question in the first paragraph, you can use this command to bring the port 4040 running in a remote server to your local computer:

$ ssh -L 4040: server.tld

This will forward the port 4040 running in remote server’s So you can access the remote server from your loopbackl address.

By default, ssh binds to the loopback address. If you want, for any reason, bind the forwarded port to another address, prefix the local port with the address, like this:

$ ssh -L server.tld

To forward a port, it must go to the another server, creating a tunnel, if you created this forwarding rule with a firewall rule or another software like socat or netcat, the traffic will be unencrypted. SSH is a secure protocol, and all the outgoing and incoming traffict that comes from the tunnel will be encrypted.

You’ll notice that everytime you want to forward a port a new ssh connection will be open, and will create another prompt, you can send the thing to background combining the -F and -n flag.

Forwaring ports from an existing connection

A feature of ssh that cured my depression is the fact that if you type “~C” (that’s literally typing a tilde and a capital c in a ssh window) it will prompt the ssh commandline, in which you can type “?” to get the usage of the commandline.

Creating hosts

I have this friend that edits the /etc/hosts file to add the hostname of his servers to the system’s DNS so he can just type ssh <servername> to ssh to the server. I’ve told him many times that this is stupid and he should edit the ~/.ssh/config file.

As it name suggets, it is the ssh config file. And it is used to configure ssh. There are an insane ammount of options that can be used in this config file. But what’s important here is that this config file can save us many, many keystrokes in the ssh command. Here’s an example.

Host guadal
     AddressFamily inet
     RequestTTY yes
     User diego
     SetEnv SHELL=/bin/zsh
     SetEnv ZDOTDIR=/home/diego/
     SetEnv ZSHDOTDIR=/home/diego/
     SetEnv DISPLAY=:0.0
     ForwardX11 Yes

Host rguadal
     AddressFamily inet
     User root
     SetEnv SHELL=/bin/zsh

This config file needs no commentary because you can figure what every line is doing. After saving a config file i can just type “ssh guadal” to login to the server as my user and “ssh rguadal” to login as root.

Tmux and stuff

There’s this software called “byobu” that is basically a tmux that is always running in a remote server so everytime you login to your server the same session of tmux will be there, and will prompt automatically.

Thing is that one day I don’t know what I was thinking but I decided to install OpenBSD in my server, and Byobu is not available on the OpenBSD ports repository and i’m a lazy motherfucker so I won’t compile it. I fixed this issue configuring regular tmux in a fancy way.

So basically tmux works with sessions, like any other terminal multiplexer, and you can attatch to that sessions at any times, as many times as you want and with many users you want. It’s like this impossible concept of 2 things at the same place at the same moment.

I got philosophical, first, you have to login into the server and type tmux -u2 command, or just tmux, i use the -u2 flag because OpenBSD is stupid and won’t handle unicode alright without those flags.

This will create a tmux session in which you can do whatever you feel like doing in a UNIX terminal.

When you’re finish doing things in a UNIX terminal, you instead of typing “exit” or “C-d” in the terminal to log off, you detatch from the tmux session, pressing the modifier (C-b by default) and “d”. Then you exited the tmux session and can log off from the ssh session.

And when you want to get back to the tmux session you had, you can ssh to the server and type tmux -u2 a.

This steps can be saved if you type (in my case because i bothered configuring ssh, probably you have to type a different command because you used a different name) ssh guadal "tmux -u2" to create a session and ssh guadal "tmux -u2 a" to attatch to the other session.


Mastering ssh will cure your depression.