SSH in Linux: log in to a remote server and use keys

ssh opens a secure session on a remote server over the network.

Syntax

ssh user@host

Common cases

ssh alice@server             # log in to the server
ssh -p 2222 alice@server     # a non-standard port
ssh-keygen -t ed25519        # create a key pair
ssh-copy-id alice@server     # put your key on the server
scp file.txt alice@server:~  # copy a file to the server
scp alice@server:~/log.txt . # and back

How it works: log in with a key, not a password

A key pair is a private key (kept only by you, in ~/.ssh/) and a public key (placed on the server). You sign a challenge from the server with the private key, and the server checks the signature with the public key - so login needs no password and is safer. ssh-copy-id puts the public key into ~/.ssh/authorized_keys on the server. Never show or copy the private key to anyone. Servers you use often go in ~/.ssh/config, so you type a short name instead of a long line.

In the book

This topic is covered in full in the chapter SSH and remote management.

See also

Sync: rsync.