Introduction
Welcome to the world of Linux administration! As a new Linux administrator, understanding the core components and commands is crucial. This detailed guide will help you get started with essential Linux tasks and concepts.

Understanding the Linux Filesystem Hierarchy
Linux uses a hierarchical filesystem structure. Here are some key directories:

• /: The root directory, where everything begins.
• /bin: Essential command binaries (e.g., ls, cp).
• /sbin: Essential system binaries (e.g., iptables, reboot).
• /etc: Configuration files for the system.
• /home: Home directories for users.
• /var: Variable files, like logs and databases.
• /usr: User binaries and read-only data.
• /tmp: Temporary files.

Basic Linux Commands

Navigating the Filesystem

• pwd: Print Working Directory. Shows your current directory.

  pwd

• ls: List directory contents. Use ls -l for a detailed list.

  ls
  ls -l

• cd: Change Directory.

  cd /etc
  cd /home/yourusername

File Operations

• cp: Copy files or directories.

  cp source_file destination_file
  cp -r source_directory destination_directory

• mv: Move or rename files or directories.

  mv old_name new_name
  mv file_name /path/to/new_location/

• rm: Remove files or directories. Use rm -r for directories.

  rm file_name
  rm -r directory_name

• mkdir: Create a new directory.

  mkdir new_directory

User and Group Management

Managing Users

• adduser: Add a new user.

  sudo adduser newusername

• passwd: Change user password.

  sudo passwd username

• deluser: Remove a user.

  sudo deluser username

Managing Groups

• groupadd: Add a new group.

  sudo groupadd newgroup

• usermod: Modify a user account (e.g., add a user to a group).

  sudo usermod -aG groupname username

• groups: Display group memberships for a user.

  groups username

File Permissions and Ownership

Understanding Permissions

• ls -l: Lists files with permissions.

  ls -l

The output looks like:

-rwxr-xr-- 1 owner group size date time filename

• r (read), w (write), x (execute) for user (owner), group, and others.

Changing Permissions

• chmod: Change file permissions.

  chmod u+x filename  # Add execute permission for the user
  chmod g-w filename  # Remove write permission for the group
  chmod o+r filename  # Add read permission for others
  chmod 755 filename  # Set permissions to rwxr-xr-x

Changing Ownership

• chown: Change file owner and group.

  sudo chown newowner:newgroup filename
  sudo chown newowner filename
  sudo chown :newgroup filename

Process Management

Viewing Processes

• ps: Report a snapshot of current processes.

  ps aux

• top: Display Linux tasks.

  top

• htop: Interactive process viewer (requires installation).

  sudo apt install htop
  htop

Managing Processes

• kill: Terminate a process.

  kill PID
  kill -9 PID  # Force kill

• pkill: Kill processes by name.

  pkill process_name

Network Management

Viewing Network Configuration

• ifconfig: Interface configuration (use ip in newer systems).

  ifconfig
  ip addr show

• ping: Check connectivity.

  ping 8.8.8.8

Managing Network Interfaces

• ifup and ifdown: Bring network interfaces up or down.

  sudo ifup eth0
  sudo ifdown eth0

Package Management

Debian-Based Systems (e.g., Ubuntu)

• apt-get: Package handling utility.

  sudo apt-get update  # Update package lists
  sudo apt-get upgrade  # Upgrade all packages
  sudo apt-get install package_name  # Install a package
  sudo apt-get remove package_name  # Remove a package
  sudo apt-get autoremove  # Remove unnecessary packages

Red Hat-Based Systems (e.g., CentOS)

• yum: Package manager for RPM-based distributions.

  sudo yum update  # Update package lists
  sudo yum upgrade  # Upgrade all packages
  sudo yum install package_name  # Install a package
  sudo yum remove package_name  # Remove a package
  sudo yum autoremove  # Remove unnecessary packages

System Monitoring and Logs

Viewing Logs

• dmesg: Print kernel ring buffer messages.

  dmesg

• journalctl: Query and display messages from the journal.

  journalctl

• Log files are generally located in /var/log/. For example:

  cat /var/log/syslog  # View system log
  tail -f /var/log/syslog  # Continuously view the latest log entries

Shell Scripting

Creating a Basic Shell Script

1. Create a new file with a .sh extension.

  nano myscript.sh

2. Add the following content:

  #!/bin/bash
  echo "Hello, World!"

3. Save and exit (Ctrl+X, then Y, then Enter).
4. Make the script executable.

  chmod +x myscript.sh

5. Run the script.

  ./myscript.sh

Conclusion
These foundational commands and concepts are essential for every Linux administrator. As you become more comfortable, you’ll explore advanced topics like shell scripting, system security, and automation. Remember, the man command is your friend for detailed information about any command:

man command_name

I hope this guide serves as a valuable resource as you begin your journey as a Linux administrator!