SSH Cheat Sheet

Whether you need a quick recap of SSH commands or you’re learning SSH from scratch, this guide will help. SSH is a must-have tool for network administrators and anyone who needs to log in to remote systems securely.

🔑 What Is SSH?

SSH (Secure Shell / Secure Socket Shell) is a network protocol that allows secure access to network services over unsecured networks.

Key tools included in the suite:

ssh-keygen → Create SSH authentication key pairs.
scp (Secure Copy Protocol) → Copy files securely between hosts.
sftp (Secure File Transfer Protocol) → Securely send/receive files.

By default, an SSH server listens on TCP port 22.

📝 Basic SSH Commands

Command	Description
`ssh user@host`	Connect to remote server
`ssh pi@raspberry`	Connect as `pi` on default port 22
`ssh pi@raspberry -p 3344`	Connect on custom port 3344
`ssh -i /path/file.pem admin@192.168.1.1`	Connect using private key file
`ssh root@192.168.2.2 'ls -l'`	Execute remote command
`ssh user@192.168.3.3 bash < script.sh`	Run script remotely
`ssh friend@Best.local "tar cvzf - ~/ffmpeg" > output.tgz`	Download compressed directory

🔐 Key Management

Command	Description
`ssh-keygen`	Generate SSH keys
`ssh-keygen -F [host]`	Find entry in `known_hosts`
`ssh-keygen -R [host]`	Remove entry from `known_hosts`
`ssh-keygen -y -f private.key > public.pub`	Generate public key from private
`ssh-keygen -t rsa -b 4096 -C "email@example.com"`	Generate new RSA 4096-bit key

📂 File Transfers

SCP (Secure Copy)

Command	Description
`scp user@server:/file dest/`	Copy remote → local
`scp file user@server:/path`	Copy local → remote
`scp user1@server1:/file user2@server2:/path`	Copy between two servers
`scp -r user@server:/folder dest/`	Copy directory recursively
`scp -P 8080 file user@server:/path`	Connect on port 8080
`scp -C`	Enable compression
`scp -v`	Verbose output

SFTP (Secure File Transfer)

Command	Description
`sftp user@server`	Connect to server via SFTP
`sftp -P 8080 user@server`	Connect on port 8080
`sftp -r dir user@server:/path`	Recursively transfer directory

⚙️ SSH Configurations & Options

Command	Description
`man ssh_config`	SSH client configuration manual
`cat /etc/ssh/ssh_config`	View system-wide SSH client config
`cat /etc/ssh/sshd_config`	View system-wide SSH server config
`cat ~/.ssh/config`	View user-specific config
`cat ~/.ssh/known_hosts`	View logged-in hosts

SSH Agent & Keys

Command	Description
`ssh-agent`	Start agent to hold private keys
`ssh-add ~/.ssh/id_rsa`	Add key to agent
`ssh-add -l`	List cached keys
`ssh-add -D`	Delete all cached keys
`ssh-copy-id user@server`	Copy keys to remote server

🖥️ Remote Server Management

After logging into a remote server:

cd → Change directory
ls → List files
mkdir → Create directory
mv → Move/rename files
nano/vim → Edit files
ps → List processes
kill → Stop process
top → Monitor resources
exit → Close SSH session

🚀 Advanced SSH Commands

X11 Forwarding (GUI Apps over SSH)

Client ~/.ssh/config:

Host *
  ForwardAgent yes
  ForwardX11 yes

Server /etc/ssh/sshd_config:

X11Forwarding yes
X11DisplayOffset 10
X11UseLocalhost no

Command	Description
`sshfs user@server:/path /local/mount`	Mount remote filesystem locally
`ssh -C user@host`	Enable compression
`ssh -X user@server`	Enable X11 forwarding
`ssh -Y user@server`	Enable trusted X11 forwarding

🔒 SSH Tunneling

Local Port Forwarding `-L`

ssh -L local_port:destination:remote_port user@server

Example: ssh -L 2222:10.0.1.5:3333 root@192.168.0.1

Remote Port Forwarding `-R`

ssh -R remote_port:destination:destination_port user@server

Example: ssh -R 8080:192.168.3.8:3030 -N -f user@remote.host

Dynamic Port Forwarding `-D` (SOCKS Proxy)

ssh -D 6677 -q -C -N -f user@host

ProxyJump `-J` (Bastion Host)

ssh -J user@proxy_host user@target_host

🛡️ Security Best Practices

Disable unused features: AllowTcpForwarding no, X11Forwarding no.
Change default port from 22 to something else.
Use SSH certificates with ssh-keygen.
Restrict logins with AllowUsers in sshd_config.
Use bastion hosts for added security.

✅ Conclusion

This cheat sheet covered:

Basic SSH connections
File transfers (SCP/SFTP)
Key management & configs
Remote management commands
Advanced tunneling & forwarding

SSH remains an indispensable tool for IT professionals and security practitioners.

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