Editing SSH Tunnel

== Objective ==

Create an SSH tunnel on a local machine which redirects MySQL requests to another machine on the LAN.

== Establish SSH Tunnel ==

Use `ssh` to create the tunnel that open up a socket listening to a port on the local machine and forward request to that local port to the port specified on the remote machine. <ref>[https://www.studytonight.com/post/how-to-setup-ssh-tunneling-in-mac-os-or-ubuntu How to Setup SSH Tunneling in Mac OS or Ubuntu]</ref>

<pre>
$ ssh -fN -L 8888:[REMOTE_SERVER]:3307 -p [NONSTANDARD_SSH_PORT] [USER]@[REMOTE_SERVER]
</pre>

* `-f` Run the ssh command in the background
* `-N` Don't execute any commands on the remote machine. Just forward the port.
* `-L` Binds the local port to the remote port. <ref>[https://explainshell.com/explain?cmd=ssh+-L+-N+-f+-l SSH options] - explainshell.com</ref>
* `-p` Non standard SSH port number. This is for establishing the SSH connection with the remote host. It has nothing to do with the port forwarding.
* 8888 is an arbitrary non-standard MySQL/MariaDB port to open on the local machine. Requests to this port are forwarded to the remote machine.
* 3307 is the port on the remote machine to which requests will be forwarded, e.g. 3307, the standard MariaDB port.

== Troubleshooting ==

=== View SSH tunnels ===

<pre>
$ lsof -i tcp | grep ^ssh

ssh       18250 damien    3u  IPv4 0xf863dcf7cc3dd6d5      0t0  TCP 192.168.123.105:56935->ds920:21098 (ESTABLISHED)
ssh       18250 damien    5u  IPv6 0xf863dcf7ce5b1e1d      0t0  TCP localhost:ddi-tcp-1 (LISTEN)
ssh       18250 damien    6u  IPv4 0xf863dcf7c661454d      0t0  TCP localhost:ddi-tcp-1 (LISTEN)
</pre>

=== Destroy an SSH tunnel ===

Find the process id of the ssh tunnel. <ref>[https://stackoverflow.com/a/9532938 How do I close this SSH tunnel?] - StackOverflow</ref>

<pre>
$ ps aux | grep [LOCAL_PORT_NUMBER]
</pre>

Kill the process of the ssh tunnel.

<pre>
$ kill -9 [PID]
</pre>

== See Also ==
=== Reference ===
<references />