# SSH Notes

## SSH Tunneling

### Local Forwarding

#### Examples

NOTE: these use autossh to prevent the tunnel from dying

Plex

```shell
autossh -f -nNT -p3141 -N -L 8080:192.168.0.209:32400 chawley@aristotle.planethawleywood.com
```

ESXi

```shell
autossh -f -nNT -p3141 -N -L 8090:192.168.0.208:443 chawley@aristotle.planethawleywood.com
```

Both ESXi and AWX

```shell
autossh -f -nNT -p3141 -N -L 8090:192.168.0.208:443 -L 8091:192.168.0.25:80 chawley@aristotle.planethawleywood.com
```

Both Plex and Derry OD

```shell
autossh -f -nNT -p3141 -N -L 8080:192.168.0.209:32400 -L 8070:192.168.0.209:80 chawley@aristotle.planethawleywood.com
```

---


<table>
  <tr>
   <td><strong>Protocol</strong>
   </td>
   <td>SSH
   </td>
  </tr>
  <tr>
   <td><strong>From</strong>
   </td>
   <td>my office workstation
   </td>
  </tr>
  <tr>
   <td><strong>To</strong>
   </td>
   <td>RRD Jumpbox (54.84.9.50)
   </td>
  </tr>
  <tr>
   <td><strong>Via</strong>
   </td>
   <td>chawley2@ladmin2
   </td>
  </tr>
  <tr>
   <td><strong>Notes</strong>
   </td>
   <td> I have the jumpbox host configured in.ssh/config on both machines
   </td>
  </tr>
  <tr>
   <td colspan="2" ><strong><code>ssh -N -L 8090:54.184.92.50:22 chawley2@ladmin2.precisiondm.com</code></strong>
   </td>
  </tr>
</table>



<table>
  <tr>
   <td><strong>Protocol</strong>
   </td>
   <td>web
   </td>
  </tr>
  <tr>
   <td><strong>From</strong>
   </td>
   <td>my office workstation
   </td>
  </tr>
  <tr>
   <td><strong>To</strong>
   </td>
   <td>Plex (derry)
   </td>
  </tr>
  <tr>
   <td><strong>Via</strong>
   </td>
   <td>chawley@aristotle
   </td>
  </tr>
  <tr>
   <td colspan="2" ><strong><code>ssh -p3141 -N -L 8080:192.168.0.209:32400 chawley@aristotle.planethawleywood.com</code></strong>
   </td>
  </tr>
</table>


### Remote Forwarding

NOTE: By default, OpenSSH only allows connecting to remote forwarded ports from the server host. However, the GatewayPorts option in the server configuration file sshd_config can be used to control this. 

The following alternatives are possible:

```shell
GatewayPorts no
```

This prevents connecting to forwarded ports from outside the server computer.

```shell
GatewayPorts yes
```

This allows anyone to connect to the forwarded ports. If the server is on the public Internet, anyone on the Internet can connect to the port.

#### Examples

<table>
  <tr>
   <td><strong>Protocol</strong>
   </td>
   <td>web
   </td>
  </tr>
  <tr>
   <td><strong>From</strong>
   </td>
   <td>derry
   </td>
  </tr>
  <tr>
   <td><strong>To</strong>
   </td>
   <td>overlook
   </td>
  </tr>
  <tr>
   <td><strong>Notes</strong>
   </td>
   <td>This allows you to access apache web pages on derry by visiting <code>http://overlook.planethawleywood.com:8888</code> as long as <code>GatewayPorts yes</code> is present in <code>/etc/ssh/sshd_config</code> (as explained above) and port 8888 is open on Overlook
   </td>
  </tr>
  <tr>
   <td colspan="2" ><strong><code>ssh -R 8888:localhost:80 root@overlook</code></strong>
   </td>
  </tr>
</table>

### Reference

* [How To Use SSH Tunneling](https://www.howtogeek.com/168145/how-to-use-ssh-tunneling/)
* [SSH Port Forwarding Example](https://www.ssh.com/ssh/tunneling/example)


## Kill Unresponsive SSH

### Summary

Let’s say you’re happily typing in your remote shell when all of a sudden, the crappy Wi-Fi network you’re using goes down. You end up with a perfectly unusable frozen shell, ugh!

To do that, assuming you lost connectivity, press in that order:


```shell
[Enter]
~
.
```


That is, &lt;return key> then tilde then period

This will send an escape sequence to your local SSH client and terminate the connection.—So this will always work even without a network connection.

Here’s the list of escape sequences:


### Supported escape sequences:

`~.` - terminate connection (and any multiplexed sessions) \
`~B` - send a BREAK to the remote system \
`~C` - open a command line \
`~R` - Request rekey (SSH protocol 2 only) \
`~^Z `- suspend ssh \
<code>~<em>#</em></code> - list forwarded connections \
<code>~&</code> - background ssh (when waiting for connections to terminate) \
<code>~?</code> - this message \
<code>~~</code> - send the escape character by typing it twice \
 \
(Note that escapes are only recognized immediately after newline.)


## SSH Keygen

### Generate an SSH Key with a comment

```shell
ssh-keygen -C "comment" -f <file>
```