Running SSH port forwarding in the background

Jupyter Notebook is essential for interacting with data. Even better, you can run it on a server (that has your data, more processors, more RAM, …) but access it from anywhere. By default, Jupyter only serves data to localhost on port 8888. Instead of opening your server to the world, you can set up port forwarding over ssh to piggy-back on the security it provides.

ssh -L 8888:localhost:8888 user@hostname

This either (a) wastes a whole terminal to keep your ssh session alive or (b) causes you to use the ssh session, forget that it’s sustaining your notebook, close the connection, and watch in horror as your notebook loses all connection to its kernel. The solution is to open your connection in the background. You can tell ssh to run in the background with -fNT

ssh -fNT -L 8888:localhost:8888 user@hostname

Now you can’t ever close the connection! SSH can set up a “master” socket and query it from a “control” socket.

ssh -M -S my-socket-name -fNT -L 8888:localhost:8888 user@hostname
ssh -S my-socket-name -O check user@hostname
>> Master running (pid=3517) 
ssh -S my-socket-name -O exit user@hostname
>> Exit request sent.

Set up config

For a particular host, you can tell it to always use a pre-named control socket with no ill effects. Edit .ssh/config:

Host hostname
    HostName hostname
    ControlPath ~/.ssh/hostname.ctl

You can make things really easy with a couple of aliases. Edit .bashrc:

alias hname-up='ssh -fNTML 8888:localhost:8888 hostname'
alias hname-status='ssh -TO check hostname'
alias hname-down='ssh -TO exit hostname'

Reference

-f
Run in the background before command execution.
-N
Don’t execute any commands
-T
Disable pseudo-tty allocation. I don’t know what this means.
-S socketname
Use a control socket with name socketname
-M
Put control socket in master mode
-O check, exit
Control command

Sources