This post is part of my Buildables Fellowship.

Basic Linux Commands

Linux commands are the foundation of system administration and cybersecurity work. Understanding these basic commands is essential for anyone working in IT or cybersecurity, as Linux is widely used in servers, security tools, and enterprise environments.

Navigation Commands

ls - List Directory Contents

The ls command displays the contents of a directory, showing files and folders in the current or specified location.

ls          # List files in current directory
ls -l       # List with detailed information (permissions, size, date)
ls -la      # List all files including hidden ones with details
ls -lh      # List with human-readable file sizes

cd - Change Directory

The cd command allows you to navigate between directories in the file system.

cd /home/user    # Change to specific directory
cd ..            # Go up one directory level
cd ~             # Go to home directory
cd -             # Go back to previous directory

pwd - Print Working Directory

The pwd command shows your current location in the file system - the full path of where you are right now.

pwd
# Output: /home/username/Documents

Common Command Line Tools

netstat - Network Statistics

The netstat command displays network connections, routing tables, and network statistics. It’s crucial for monitoring network activity and troubleshooting connectivity issues.

netstat -tuln    # Show all listening ports (TCP and UDP)
netstat -an      # Show all connections and listening ports
netstat -rn      # Show routing table

What it does:

• Shows active network connections
• Displays listening ports and services
• Provides routing information
• Helps identify suspicious network activity

ping - Network Connectivity Test

The ping command tests connectivity between your system and a target host by sending ICMP echo request packets.

ping google.com       # Ping a website
ping -c 4 8.8.8.8    # Ping with limited packet count
ping 192.168.1.1     # Ping local gateway

What it does:

• Tests if a host is reachable
• Measures round-trip time
• Shows packet loss statistics
• Verifies DNS resolution

ifconfig - Interface Configuration

The ifconfig command displays and configures network interface parameters. On newer systems, ip command is often preferred.

ifconfig              # Show all network interfaces
ifconfig eth0         # Show specific interface
ifconfig eth0 up      # Enable interface
ifconfig eth0 down    # Disable interface

What it does:

• Displays network interface information
• Shows IP addresses, MAC addresses
• Configures network interfaces
• Enables/disables network interfaces

whoami - Current User Identity

The whoami command displays the username of the currently logged-in user.

whoami
# Output: username

What it does:

• Shows current user identity
• Useful in scripts to verify user context
• Helps when switching between users

User Management

Creating a New User

The adduser command creates a new user account on the system. This requires administrative privileges.

sudo adduser testuser

What it does:

• Creates a new user account
• Sets up home directory
• Prompts for password and user information
• Adds user to default groups

Process:

1. Creates user entry in /etc/passwd
2. Creates home directory (/home/testuser)
3. Copies default configuration files
4. Sets up initial permissions

Permissions Management

Creating a Directory and Setting Ownership

sudo mkdir /home/testfolder

What it does: Creates a new directory called “testfolder” in the /home directory.

Changing Ownership

sudo chown testuser:testuser /home/testfolder

What it does: Changes the ownership of /home/testfolder to user testuser and group testuser. The format is user:group.

Setting Permissions

sudo chmod 700 /home/testfolder

What it does: Sets permissions to 700, which means:

• 7 (owner): read, write, execute (4+2+1)
• 0 (group): no permissions
• 0 (others): no permissions

Permission Numbers Explained

Linux permissions use a three-digit octal system:

• 4 = read permission
• 2 = write permission
• 1 = execute permission

Common permission combinations:

• 755: Owner can do everything, group and others can read and execute
• 644: Owner can read and write, group and others can only read
• 700: Only owner has full access, no access for group or others
• 600: Only owner can read and write, no access for anyone else

These basic commands form the foundation of Linux system administration.