SSH

SSH: Origins and Introduction

Secure Shell (SSH) was developed by the IETF's Network Working Group. SSH is a security protocol built on top of the application and transport layers, providing a secure transport and working environment for the shell on a computer.

SSH is currently one of the more reliable protocols designed specifically to secure remote login sessions and other network services. Using SSH effectively prevents information leaks during remote administration. SSH encrypts all transmitted data and also helps prevent DNS spoofing and IP spoofing.

Using SSH

My examples mainly use a Mac connecting to an Ubuntu host

1. Connecting to a Remote Host

Regular Users

ssh user@1.2.3.4, press Enter, type your password, and you're logged in to the remote host.

Lazy Users

Typing a password is a hassle, so use an RSA key
Generate a key on your Mac, then view and copy it with these commands

ssh-keygen -t rsa generates the key; just press Enter through the defaults
cat ~/.ssh/id_rsa.pub shows the generated key so you can copy it. That's all done locally on the Mac.

Then log in to the VPS, go to the .ssh directory, and paste the key

1 2	cd .ssh vim authorized_keys

Still too much hassle? Is there a way to skip copy and paste? Of course. One command copies the key to the right file
ssh-copy-id user@1.2.3.4

Ultra-Lazy Users

Nice, no more typing the password every time. But you still have to type ssh user@1.2.3.4. If you can skip the password, you can skip this too. Create a file called test-ssh, put ssh user@1.2.3.4 in it, save and exit, then make it executable with chmod 755 test-ssh. Now just run ./test-ssh to log in to the VPS

2. Run Remote Commands Locally

Run commands on the VPS from your local machine without logging in. For example, to create a file
ssh user@1.2.3.4 'touch test'
creates the file. If you need root privileges, add the -t flag
ssh -t user@1.2.3.4 'touch test'

3. Remote Copy

To download file a from the home directory on the VPS to my Downloads folder, use the scp command
scp -r user@1.2.3.4:~/a ~/Downloads

To upload the local file test to the aa directory under the VPS home directory, do the same
scp -r ~/test user@1.2.3.4:~/aa