Linux SSH Commands

Overview

SSH (Secure Shell) is a protocol used to securely access and manage remote systems over a network. The SSH suite of commands provides a variety of tools for connecting to, configuring, and managing remote systems. This document covers basic and commonly used SSH commands.

Basic SSH Commands

ssh

Used to securely connect to a remote machine.

ssh <user>@<hostname_or_ip>

Example

ssh john@192.168.1.100
# Connects to the remote host 192.168.1.100 as user 'john'

ssh-keygen

Generates a new SSH key pair.

ssh-keygen

Example

ssh-keygen
# Prompts to generate a new SSH key pair; saves the private key and public key in the default location (~/.ssh/)

ssh-copy-id

Copies your SSH public key to a remote host's authorized keys.

ssh-copy-id <user>@<hostname_or_ip>

Example

ssh-copy-id john@192.168.1.100
# Copies the public key to the remote host to enable passwordless login for user 'john'

scp

Securely copies files between hosts over SSH.

scp <source> <user>@<hostname_or_ip>:<destination>

Example

scp localfile.txt john@192.168.1.100:/home/john/
# Copies 'localfile.txt' from the local machine to the '/home/john/' directory on the remote host

sftp

Secure File Transfer Protocol for transferring files over SSH.

sftp <user>@<hostname_or_ip>

Example

sftp john@192.168.1.100
# Opens an SFTP session with the remote host

ssh-add

Adds SSH private keys to the SSH authentication agent.

ssh-add <key_file>

Example

ssh-add ~/.ssh/id_rsa
# Adds the private key 'id_rsa' to the SSH agent for authentication

ssh-agent

Manages SSH keys and handles authentication for SSH sessions.

eval $(ssh-agent)

Example

eval $(ssh-agent)
# Starts the SSH agent and sets environment variables for the current session

Advanced SSH Commands

ssh -i

Specifies a private key file to use for authentication.

ssh -i <private_key_file> <user>@<hostname_or_ip>

Example

ssh -i ~/.ssh/id_rsa john@192.168.1.100
# Connects to the remote host using the specified private key file

ssh -p

Specifies a port number for the SSH connection.

ssh -p <port_number> <user>@<hostname_or_ip>

Example

ssh -p 2222 john@192.168.1.100
# Connects to the remote host on port 2222

ssh -L

Creates a local port forwarding.

ssh -L <local_port>:<remote_host>:<remote_port> <user>@<hostname_or_ip>

Example

ssh -L 8080:localhost:80 john@192.168.1.100
# Forwards local port 8080 to port 80 on the remote host through SSH

ssh -R

Creates a remote port forwarding.

ssh -R <remote_port>:<local_host>:<local_port> <user>@<hostname_or_ip>

Example

ssh -R 9090:localhost:80 john@192.168.1.100
# Forwards remote port 9090 to port 80 on the local machine through SSH

ssh -C

Enables compression for the SSH connection.

ssh -C <user>@<hostname_or_ip>

Example

ssh -C john@192.168.1.100
# Connects to the remote host with compression enabled

Summary

The SSH suite of commands provides powerful tools for securely managing and transferring data between systems. By mastering these commands, you can effectively perform remote administration and file transfers while maintaining secure connections. For more detailed information on each command, refer to the Linux manual pages.