Use SSH to remotely access a device

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SSH: Secure Shell is an encrypted protocol for a remote shell login. See wikipedia:Secure shell

Ways to SSH

Using a terminal, you may SSH through:

  • a local network, by targeting a local IP address
  • a public network, by targeting a public IP address
  • generating and authorising matching public and private keys

SSH over local IP

To find the IP address of a computer on the local network, such as a Raspberry Pi, boot it and connect it to a screen. Type the command: 

ifconfig

If connected over wifi, you should look for the IP listed next to wlan0

In this instance it is 192.168.1.101 

inet 192.168.1.101

Now, on another machine you can remotely SSH to a user account on the Raspberry Pi (one that you know the password of).

In this instance, we SSH to the Pi user account on the Raspberry Pi by typing: 

ssh pi@192.168.1.101

The first time you do this, an ECDSA key fingerprint is created on your machine, and 192.168.1.101 (ECDSA) is added to a list of known hosts in the file

~/.ssh/known_hosts

It will ask you for a password (most often you won't see what you write, so type carefully), and if it is correct you can access the device.

You are still using the local network, but you (and others who SSH to other accounts on the same network) can now control the Raspberry Pi remotely.

SSH over public IP

Using a public IP address is much the same as a local IP address; however:

  • to access it you have to use the Internet which means going "outside" your local area network. This can be confusing when you are self-hosting a service on a machine that is sitting right next to you physically, but has an IP address located on the wide area network.

You can always SSH by entering the public IP address and the correct user credentials each time, however if it is something you have to do often it may be more convenient to generate public and private key pairs using Open SSH.

Generating SSH key pairs

Creating, using and managing ssh keys

SSH configuration file

The SSH configuration file makes it a lot simpler to ssh scp or sshfs. It is especially convenient when you have keys for different servers. It helps you to keep them organised and to ssh into servers with easy to remember shortcuts.

Rather than typing 

scp myfile username@host:/path/to/copy/file/to

We can simply do with 

scp myfile hostname:/path/to/copy/file/to

Location of the .ssh directory

On Linux-based distributions: /home/<your username>/.ssh

On MacOS: Users/<your username>/.ssh

Create ssh configuration file ~/.ssh/config/

Create the file: 

touch ~/.ssh/config

Open the file in your favourite text editor and insert: 

Host hostname // name for the shortcut you use to ssh into the server
User usename // ssh user
Hostname 192.168.10.20 // hostname of the server
Port 22
Identityfile ~/.ssh/id_rsa // change and make sure this is the path to the location of your keys
Serveraliveinterval 30

Now you can use the short cut to ssh, scp, sshfs to that and any other host in in .ssh/config

using only 

ssh username@hostname

or even 

ssh hostname

SSHFS: SSH File System

SSHFS: SSH File System

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