Use SSH to remotely access a device

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 a local network

To SSH to a computer on a local network, first find the local, or private IP address. 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.

Create a new key for your machine

ssh-keygen -t rsa

CHOOSE A STRONG PASSPHRASE, EMPTY PASSPHRASE == BAD

If someone has access to your machine via social engineering or tech exploit, your key can be stolen and used to login in all the machines and services without password.

Install your key on the machines where you need to log in

Handy function to put in your shell config

In your shell resource file (~/.zhrc, ~/.bashrc,...) add the following function:

ssh-install-key() {
    cat ~/.ssh/id_rsa.pub | ssh ${1} "cat - >> ~/.ssh/authorized_keys"
}

Now you can install your main key, id_rsa.pub, directly to a target machine:

ssh-install-key username@super.server.nl

Using your keys

With keychain

Keychain is a software that will keep track of which keys are available in your system and will only ask your passphrase once per session instead. It is a front-end to ssh-add and ssh-agent.

Add the following in your shell resource file:

if [ -e ~/.ssh/id_rsa ]
then
    keychain --quiet --nogui ~/.ssh/id_rsa
    . ~/.keychain/${HOSTNAME}-sh
fi

Now restart your session and you will be prompted, once for your passphrase. After that you can directly ssh/scp to the machines where your installed your key and you will not be prompted for any passwords!

ssh username@super.server.nl

Using aliases for your SSH connections

To make your life even easier you can edit (create if non existent) the ~/.ssh/config file to create Host SSH aliases for the machines you need to connect to. You can also pass all the SSH options you might want to add, for instance:

Host super
    User username
    Hostname super.server.nl

Host super2
    User anotherusername
    Hostname super.serverl.nl
    Port 12345
    ForwardAgent yes

Now when you want to ssh/scp to your server you can just do the following:

ssh super

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 username // 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 Filesystem) is a filesystem client for mounting remote directories on your machine, using an SSH connection.

By using it you can access, read, edit files from a remote machine on your local machine, as long as you have an account in the remote machine.

Installing

On Debian/Ubuntu

sudo apt update
sudo apt install sshfs

On Mac

Use homebrew. If homebrew is not installed run the installation command:

/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

Once brew is installed, run:

brew cask install osxfuse
brew install sshfs

Mounting the Remote File System with SSHFS

SSHFS command essential parameters:

sshfs user@host:remote_directory local_mount_directory

How to mount

Create a directory in your local machine, to be use as a mount point

mkdir ~/remote

Mount host remote directory onto the ~/remote directory

ssh user@host:/full/path/to/remote/dir ~/remote

That's it :)

How to unmount

To unmount the remote dir from the local directory we use the umount NOT unmount, BUT umount

umount ~/remote