Persistent SSH Sessions

If you win the lottery and start a job working as a penetration tester the chances are you will need to learn a couple of vital lessons sharpish. One that I like to drill into people is about SSH sessions that persist even if your client connection dies. A complete rookie mistake – that we all make – is to lose data when our SSH connection dies. Maybe the Wi-Fi disconnects or you close your laptop to go for lunch? Who knows.

Don’t blame yourself. The chances are you partly educated yourself and you were using either a Linux base machine or a VM. In that scenario your terminal lives as long as you want it to with no questions asked.

Now that you are on someone’s payroll the chances are you have a fancy “penetration testing lab” that you have to send connections through for legal reasons. While I like that I won’t lose my liberty it does introduce this complexity into our lives.

Tmux

I am a relative noob to Tmux but it really seems to be worth the investment of time.

If I had a time machine I would get future me who understands Tmux completely to come and teach me. Maybe in a fancy silver car with a… I am gonna say it… *pffft*. Ok ok, calm down. In a fancy silver car with a tmux-capacitor! I know some of you liked that pun and that means you are as bad as me.

The absolute basics are these three commands:

tmux new -s <session_name>    # used to establish a new session.
tmux new -s customerA         # I name a session after the project for ease.
tmux ls                       # list the sessions that exist
tmux attach -t <session_name> # used to attach to your previous session
tmux attach -t customerA      # attaching back to the session created last time.

If you create a new session you can then kill your client SSH connection by disconnecting from Wi-Fi or whatever. On reconnecting when back online you attach to that and you have lost nothing (assuming the server has remained online and the issue was client side only).

For the purposes of this tutorial you have done all you need to do to prevent yourself losing work. Go you.

However, Tmux is capable of lots more things such as splitting an SSH session horizontally and/or vertically when you want to show two processes at once in a screenshot. Or what about having multiple “windows” in a single SSH session and a relatively easy way to move between those windows? Instead of having additional instances of Putty on windows or tabs in “MTPutty” you can do everything over a single SSH session inside of Tmux.

There is a full cheat sheet here.

https://tmuxcheatsheet.com/

Totally worth the learning curve.

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