SSH

This quick reference cheat sheet provides various for using SSH.

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#Getting Started

#Connecting

Connect to a server (default port 22)

$ ssh [email protected]

Connect on a specific port

$ ssh [email protected] -p 6222

Connect via pem file (0400 permissions)

$ ssh -i /path/file.pem [email protected]

See: SSH Permissions

#Executing

Executes remote command

$ ssh [email protected] 'ls -l'

Invoke a local script

$ ssh [email protected] bash < script.sh

Compresses and downloads from a server

$ ssh [email protected] "tar cvzf - ~/source" > output.tgz

#SCP

Copies from remote to local

$ scp user@server:/dir/file.ext dest/

Copies between two servers

$ scp user@server:/file user@server:/dir

Copies from local to remote

$ scp dest/file.ext user@server:/dir

Copies a whole folder

$ scp -r user@server:/dir dest/

Copies all files from a folder

$ scp user@server:/dir/* dest/

Copies from a server folder to the current folder

$ scp user@server:/dir/* .

#Config location

File Path Description
/etc/ssh/ssh_config System-wide config
~/.ssh/config User-specific config
~/.ssh/id_{type} Private key
~/.ssh/id_{type}.pub Public key
~/.ssh/known_hosts Known Servers
~/.ssh/authorized_keys Authorized login key

#SCP Options

Options Description
scp -r Recursively copy entire directories
scp -C Compresses data
scp -v Prints verbose info
scp -P 8080 Uses a specific Port
scp -B Batch mode (Prevents password)
scp -p Preserves times and modes

#Config sample

Host server1
    HostName 192.168.1.5
    User root
    Port 22
    IdentityFile ~/.ssh/server1.key

Launch by alias

$ ssh server1

See: Full Config Options

#ProxyJump

$ ssh -J proxy_host1 remote_host2

$ ssh -J user@proxy_host1 user@remote_host2

Multiple jumps

$ ssh -J user@proxy_host1:port1,user@proxy_host2:port2 user@remote_host3

#ssh-copy-id

$ ssh-copy-id user@server

Copy to alias server

$ ssh-copy-id server1

Copy specific key

$ ssh-copy-id -i ~/.ssh/id_rsa.pub user@server

#SSH keygen

#ssh-keygen

$ ssh-keygen -t rsa -b 4096 -C "[email protected]"
- - -
-t Type of key
-b The number of bits in the key
-C Provides a new comment

Generate an RSA 4096 bit key with email as a comment

#Generate

Generate a key interactively

$ ssh-keygen

Specify filename

$ ssh-keygen -f ~/.ssh/filename

Generate public key from private key

$ ssh-keygen -y -f private.key > public.pub

Change comment

$ ssh-keygen -c -f ~/.ssh/id_rsa

Change private key passphrase

$ ssh-keygen -p -f ~/.ssh/id_rsa

#Key type

  • rsa
  • ed25519
  • dsa
  • ecdsa

#known_hosts

Search from known_hosts

$ ssh-keygen -F <ip/hostname>

Remove from known_hosts

$ ssh-keygen -R <ip/hostname>

#Key format

  • PEM
  • PKCS8

#SSH Tunneling

#SSH Tunnel Options

Option Description
-L Local port forwarding
-R Remote port forwarding
-D Dynamic port forwarding
-f Run in background
-N Do not execute a remote command
-g Allow remote hosts to connect to local forwarded ports

more details on flag above with man ssh

#Local Port Forwarding

# Forward a local port to a remote server
ssh -L local_port:remote_host:remote_port user@ssh_server

# Example: Forward local port 8080 to remote port 80 on example.com
ssh -L 8080:example.com:80 user@ssh_server

#Dynamic Port Forwarding

# Create a SOCKS proxy on a local port
ssh -D local_port user@ssh_server

# Create a SOCKS proxy on local port 1080 in the background
ssh -f -N -D 1080 user@ssh_server

#Background Tunnel

# Create a local port forwarding tunnel in the background
ssh -f -N -L local_port:remote_host:remote_port user@ssh_server

#Multiple Tunnels

# Create multiple tunnels in a single SSH command
ssh -L 8080:example.com:80 -L 3306:db.example.com:3306 user@ssh_server

#Combining Options

# In background, no command, allow remote host, local port forward, identity_file
ssh -f -N -g -L 8080:example.com:80 -i ~/.ssh/custom_key user@ssh_server

#Also see