$ Linux Command

Network

ssh

Connect securely to a remote machine.

sshremoteloginshellkeynetwork

Additional Notes

ssh opens a secure shell session on a remote machine. It encrypts traffic and is used for remote administration, server work, development, tunneling, and file-transfer workflows.

SSH can authenticate with passwords or keys. Key-based authentication is usually preferred for security and automation.

Syntax

ssh [options] user@host
ssh [options] host

Parameters

  • user: Remote username.
  • host: Remote hostname or IP address.
  • No user: SSH uses your current local username.

Common Options

  • -p PORT: Connect to a custom SSH port.
  • -i KEYFILE: Use a specific private key.
  • -v: Verbose output for troubleshooting.
  • -X: Enable X11 forwarding when supported.
  • -L LOCAL:HOST:PORT: Local port forwarding.
  • -R REMOTE:HOST:PORT: Remote port forwarding.
  • -N: Do not run a remote command, useful for tunnels.
  • -T: Disable pseudo-terminal allocation.
  • -o KEY=VALUE: Set a configuration option.

Examples

ssh rani@example.com

Connect as user rani.

ssh root@192.168.1.10

Connect to an IP address as root. Many systems disable root SSH login for safety.

ssh -p 2222 rani@example.com

Connect to a custom SSH port.

ssh -i ~/.ssh/lab_key rani@lab.local

Use a specific private key.

ssh -v rani@example.com

Show debugging information for connection problems.

ssh -L 8080:127.0.0.1:80 rani@example.com

Forward local port 8080 to port 80 from the remote side.

ssh rani@example.com "uptime"

Run one remote command and exit.

SSH Config Example

You can save connection settings in ~/.ssh/config:

Host lab
  HostName 192.168.1.10
  User rani
  Port 2222
  IdentityFile ~/.ssh/lab_key

Then connect with:

ssh lab

Practical Notes

  • Keep private keys secret and set strict permissions, commonly chmod 600 ~/.ssh/id_rsa.
  • Use ssh-keygen to create keys and ssh-copy-id to install a public key on a server.
  • If login fails, check username, host, port, firewall, key permissions, and server SSH configuration.
  • Use scp, sftp, or rsync -e ssh for file transfer.
  • Avoid enabling password login on public servers when key-based login is available.