ssh command

`ssh` - OpenSSH remote login client

The ssh command in Linux (Secure Shell) is a powerful tool used to securely connect to and manage remote systems over a network. It provides an encrypted connection for running commands, transferring files, or accessing a remote shell.

Usage: ssh [options] [user@]hostname [command]

user: The username on the remote system (optional if same as local user).
hostname: The remote machine’s IP address or domain name.
command: An optional command to run remotely (if omitted, you get a shell).
options: Flags that modify how ssh behaves.

Examples

Basic Connection

Connect to a remote machine with your username and its hostname or IP.
```
ssh alice@192.168.1.100
```
- Connects as user alice to the machine at 192.168.1.100.
- You’ll be prompted for alice’s password unless key-based authentication is set up.
Default User:

If your local username matches the remote one:
```
ssh 192.168.1.100
```
Running a Remote Command

Execute a single command on the remote system without starting a full shell.
```
ssh alice@192.168.1.100 "ls -l"
```
- Runs ls -l on the remote machine and displays the output locally.
- The session closes after the command finishes.
Specifying a Port

Use -p to connect to a non-default SSH port (default is 22).
```
ssh -p 2222 alice@192.168.1.100
```
- Connects to port 2222 instead of 22.
Using Key-Based Authentication

Avoid password prompts by using SSH keys.

Setup:
1. Generate a key pair locally:
```
ssh-keygen -t rsa -b 4096
```
- Press Enter for defaults (saves to ~/.ssh/id_rsa).
1. Copy the public key to the remote server:
```
ssh-copy-id alice@192.168.1.100
```
- Enter the password once to set it up.
1. Connect:
```
ssh alice@192.168.1.100
```
- No password needed now.
Verbose Output

Use -v (verbose) to debug connection issues.
```
ssh -v alice@192.168.1.100
```
- Shows detailed steps (e.g., authentication attempts).
Keeping Sessions Alive

Use -o to set options like ServerAliveInterval to prevent timeouts.
```
ssh -o ServerAliveInterval=60 alice@192.168.1.100
```
- Sends a keep-alive signal every 60 seconds.
SSH Config File

Simplify connections with a ~/.ssh/config file.

Edit ~/.ssh/config:
```
Host myserver
    HostName 192.168.1.100
    User alice
    Port 2222
```
- Then connect with:
```
ssh myserver
```
- No need to type the full command.

Common Options

Option	Description
`-p`	Specify a port
`-v`	Verbose output for debugging
`-i`	Specify an identity file (e.g., `-i ~/.ssh/mykey`)
`-o`	Set configuration options
`-X`	Enable X11 forwarding (GUI apps)
`-t`	Force a TTY (e.g., for sudo remotely)

ssh - OpenSSH remote login client​

Examples​

`ssh` - OpenSSH remote login client

Examples