🔐 SSH & Remote Work

Logging in to servers, keys instead of passwords, copying files, tunnels and sessions that survive a lost connection. OpenSSH is built into Linux, macOS and Windows 10/11.

Open in the interactive Cheat Sheets

Connecting

`ssh jernej@192.168.1.10`	Log in to a server.
`ssh -p 2222 jernej@server.example.com`	Log in on a different port.
`exit Ctrl+D`	Log out.
`Enter ~ .`	Close a frozen SSH session (three keys one after another).

Keys instead of passwords

`ssh-keygen -t ed25519 -C "jernej@laptop"`	Make a key pair. Protect it with a passphrase.
`ssh-copy-id jernej@192.168.1.10`	Linux/macOS: copy your public key to the server.
`type $env:USERPROFILE\.ssh\id_ed25519.pub \| ssh jernej@192.168.1.10 "cat >> ~/.ssh/authorized_keys"`	Windows PowerShell: the same without ssh-copy-id.
`PasswordAuthentication no`	In /etc/ssh/sshd_config on the server, after the key works – no more password logins.
`sudo systemctl restart ssh`	Apply the change (the service is called sshd on Fedora). Keep the old session open until the new login works!

~/.ssh/config – shorter commands

Host nas HostName 192.168.1.10 User jernej Port 22 A short name for a server. Then ssh nas is enough.

Copying files

`scp file.txt nas:/home/jernej/`	Copy a file to the server.
`scp -r nas:/var/www/site ./site-backup`	Copy a folder from the server to here.
`rsync -avh --progress folder/ nas:/backup/folder/`	Copy only what changed. The / at the end of folder/ matters.
`rsync -avh --delete folder/ nas:/backup/folder/`	Make the target the same as the source – deletes what is not in the source.

Tunnels

`ssh -L 8080:localhost:80 nas`	Open the server's port 80 as localhost:8080 on your computer.
`ssh -L 5432:localhost:5432 nas`	Reach a database that only listens on the server itself.

Sessions that survive (tmux)

`tmux new -s work`	Start a named session on the server.
`Ctrl+B then D`	Detach – the programs keep running after you log out.
`tmux attach -t work`	Come back to it later, even from another computer.
`tmux ls`	List sessions.