Linux Command Series: SSH

SSH (Secure Shell) is a core tool in Linux systems used for secure remote login and command execution, implementing secure communication between hosts based on encryption protocols. The default port is 22, supporting password authentication and key pair authentication, and providing features such as port forwarding and file transfer.

📌 1. `ssh` Command Basic Syntax

ssh [options] username@remote_host

Parameter	Description
`<span>-p <port></span>`	Specify the SSH port (default 22)
`<span>-i <private_key_file></span>`	Use the specified private key file
`<span>-C</span>`	Enable compression to improve performance on slow networks
`<span>-X/</span><code><span>-Y</span>`	Enable X11 forwarding (for remote GUI applications)
`<span>-L/</span><code><span>-R</span>`	Port forwarding (local/remote)

📌 2. Basic SSH Connection

🎯 2.1 Remote Login

ssh user@remote_host

📌 Example:

ssh [email protected] # Log in to the 192.168.1.1 server as root user

🎯 2.2 Specify Port

ssh -p 2222 user@remote_host

Function:If the remote server’s SSH port is not the default 22, specify the port 2222.

🎯 2.3 Passwordless Login (Using SSH Keys)

🛠️ 1️⃣ Generate SSH Key

ssh-keygen -t rsa -b 4096 -f ~/.ssh/id_rsa

Function：Generate a 4096-bit RSA key (public key id_rsa.pub and private key id_rsa).

🛠️ 2️⃣ Copy Public Key to Remote Server

ssh-copy-id user@remote_host

Function：Copy the public key ~/.ssh/id_rsa.pub to the remote ~/.ssh/authorized_keys.

After copying the public key, login without entering a password:ssh user@remote_host

🎯 2.4 Configure SSH Passwordless Alias

Edit the ~/.ssh/config file:

Host myserver
    HostName 192.168.1.1
    User root
    Port 3333
    IdentityFile ~/.ssh/id_rsa

Function：Next time you log in, just enter: ssh myserver, to connect to 192.168.1.1, without entering the full command each time.

📌 3. Remote Command Execution

🎯 3.1 Execute a Single Command on Remote Server

ssh user@remote_host "ls -lrt"

Function：Execute ls -lrt on remote_host and return the result.

🎯 3.2 Execute Multiple Commands

ssh user@remote_host "cd /var/www &amp;&amp; ls -lrt"

Function：First cd to the directory, then execute ls -lrt.

You can also use << EOF to run multiple lines of commands:

ssh user@remote_host &lt;&lt; EOF
cd /var/log
ls -la
exit
EOF

📌 4. SSH Port Forwarding

🎯 4.1 Local Port Forwarding (Access Remote Services)

ssh -L 8080:localhost:3306 user@remote_host

📌 Function:

Map local port 8080 to remote MySQL 3306
Thus, local 127.0.0.1:8080 is equivalent to accessing the remote 3306 port

Local MySQL Connection Example:mysql -h 127.0.0.1 -P 8080 -u root -p

🎯 4.2 Remote Port Forwarding (Allow Remote Access to Local Services)

ssh -R 9000:localhost:80 user@remote_host

Function:

Allow remote 9000 port to accesslocal 80 port
Suitable forallowing public servers to access internal services

Remote server access:curl http://localhost:9000

📌 5. Proxy & Jump Host

🎯 5.1 SOCKS5 Proxy (Scientific Internet Access)

ssh -D 1080 user@remote_host

Function：

Create a SOCKS5 proxy on local port 1080
Can be used for browser proxy or proxychains

🎯 5.2 Connect via Jump Host

ssh -J jump_host user@target_host

Function：

First log in through jump_host (jump host), then connect to target_host

Equivalent to:

ssh user@jump_host
ssh user@target_host

📌 6. Stop & Restart SSH Service

🎯 7.1 Stop SSH

sudo systemctl stop ssh

🎯 7.2 Start SSH

sudo systemctl start ssh

🎯 7.3 Restart SSH

sudo systemctl restart ssh

Applicable for restarting the service after modifying SSH configuration.

📌 1. <span>ssh</span> Command Basic Syntax