Linux Basics: Day 02

Architecture and File Structure of Linux

System Architecture

RHEL Linux 9 supports x86_64 (64-bit) architecture by default. It also provides support for ARM-based systems. RHEL Linux 9 uses the Linux Kernel (typically version 5.14.x) and the systemd init system.

• Package Manager: dnf (Dandified Yum)
• System Architecture: Primarily x86_64, also supports ARM and other architectures.

File System Hierarchy

The file structure in Rocky Linux 9 follows the Filesystem Hierarchy Standard (FHS), which is used across most Linux distributions. Here’s a breakdown of important directories:

1. / (Root)

• The root directory is the top-most directory in the filesystem, from which all other directories branch out.

2. /bin (Essential Binaries)

• Contains essential command binaries required for the system to boot and run.

  Example: /bin/bash, /bin/ls

3. /boot (Boot Loader Files)

• Contains files necessary for booting the system, including the kernel.

  Example: /boot/vmlinuz, /boot/grub2/

4. /dev (Device Files)

• Contains device files that represent system hardware, such as hard drives, terminals, and USB devices.

  Example: /dev/sda, /dev/null

5. /etc (Configuration Files)

• Stores system-wide configuration files for the system and applications.

  Example: /etc/passwd, /etc/hostname

6. /home (User Home Directories)

• Contains the home directories for regular users.

  Example: /home/user1/

7. /lib (Essential Libraries)

• Contains shared libraries required by binaries in /bin and /sbin.

  Example: /lib/libc.so.6

8. /media (Mount Points for Removable Media)

• Used for mounting removable media like USB drives and CD-ROMs.

  Example: /media/usb/

9. /mnt (Temporary Mount Points)

• Typically used for temporary mounts of file systems.

  Example: /mnt/data/

10. /opt (Optional Software Packages)

• Contains third-party application software packages that are not part of the core distribution.

  Example: /opt/apache/

11. /proc (Virtual Filesystem for Kernel Information)

• A virtual file system that exposes system information such as running processes and hardware configuration.

  Example: /proc/cpuinfo, /proc/meminfo

12. /root (Root User’s Home)

• The home directory for the root user.

  Example: /root/

13. /run (Runtime Information)

• Contains runtime data such as information about running processes, and other system state data.

  Example: /run/utmp

14. /sbin (System Binaries)

• Contains system binaries used for administrative tasks, typically accessible only to the root user.

  Example: /sbin/reboot, /sbin/shutdown

15. /tmp (Temporary Files)

• Used for storing temporary files created by the system or applications. Files in this directory are often deleted after reboot.

  Example: /tmp/tempfile

16. /usr (User Programs and Data)

• Contains user applications and data. It is one of the largest directories on a system.

  Example: /usr/bin, /usr/lib

17. /var (Variable Data)

• Contains variable files such as logs, spool files, and caches.

  Example: /var/log/, /var/spool/

Key Configuration Files

• Network Configuration: /etc/sysconfig/network-scripts/ifcfg-eth0
• System Users and Groups: /etc/passwd, /etc/group, /etc/shadow
• Package Management: /etc/dnf/dnf.conf
• Systemd Services: /etc/systemd/system/

1. pwd (Print Working Directory)

• Usage: pwd

• Explanation: This command prints the full path of the current working directory. It helps users confirm where they are in the directory structure.

  Example:

  $ pwd
  /home/user

2. ls (List)

• Usage: ls

• Explanation: Lists the files and directories within the current directory. By default, ls will not show hidden files (files starting with a dot). Use options like -l for detailed listing or -a for all files.

  Example:

  $ ls -la
  total 28
  drwxr-xr-x 4 user user 4096 May 10 10:45 .
  drwxr-xr-x 3 user user 4096 May 10 10:45 ..
  -rw-r--r-- 1 user user   45 May 10 10:45 file1.txt

3. cd (Change Directory)

• Usage: cd <directory-path>

• Explanation: This command allows you to change to a specified directory. If no argument is provided, it takes you to the user’s home directory.

  Example:

  $ cd /home/user/Documents

4. cp (Copy)

• Usage: cp <source> <destination>

• Explanation: Copies files or directories from the source to the destination. You can use the -r option to copy directories recursively.

  Example:

  $ cp file1.txt /home/user/backup/

5. mv (Move/Rename)

• Usage: mv <source> <destination>

• Explanation: Moves or renames files and directories. It’s also used to move files between directories.

  Example:

  $ mv oldname.txt newname.txt

6. rm (Remove)

• Usage: rm <file>

• Explanation: Removes a file. If you want to remove a directory, you must use the -r option for recursive removal.

  Example:

  $ rm -r directory_name

7. touch (Create Empty File)

• Usage: touch <file-name>

• Explanation: Creates a new empty file if it doesn’t exist. If the file exists, touch updates its timestamp.

  Example:

  $ touch newfile.txt

8. cat (Concatenate and Display File)

• Usage: cat <file-name>

• Explanation: Displays the contents of a file to the terminal. It can also be used to concatenate files together.

  Example:

  $ cat file1.txt

9. echo (Display Text)

• Usage: echo <text>

• Explanation: Displays the text to the terminal or outputs it to a file.

  Example:

  $ echo "Hello, World!"

10. man (Manual Pages)

• Usage: man <command>

• Explanation: Displays the manual or help documentation for a command.

  Example:

  $ man ls

11. chmod (Change File Permissions)

• Usage: chmod <permissions> <file>

• Explanation: Changes the permissions of a file or directory. It uses numerical values to set read, write, and execute permissions for the owner, group, and others.

  Example:

  $ chmod 755 script.sh

12. chown (Change Owner/Group)

• Usage: chown <user>:<group> <file>

• Explanation: Changes the ownership of a file or directory. You can specify a user, a group, or both.

  Example:

  $ chown user:group file.txt

13. ps (Process Status)

• Usage: ps aux

• Explanation: Displays the current running processes on your system, showing information such as process ID (PID), memory and CPU usage.

  Example:

  $ ps aux

14. top (Task Manager)

• Usage: top

• Explanation: Displays a real-time, dynamic view of the system’s running processes, including memory, CPU usage, and more.

  Example:

  $ top

15. df (Disk Free)

• Usage: df -h

• Explanation: Displays the available disk space on all mounted filesystems. The -h option makes the output human-readable.

  Example:

  $ df -h

16. free (Memory Usage)

• Usage: free -h

• Explanation: Displays the amount of free and used memory in the system.

  Example:

  $ free -h

17. uname (System Information)

• Usage: uname -a

• Explanation: Displays the system information, including the kernel version, architecture, and other details.

  Example:

  $ uname -a

18. hostname (Get/Set Hostname)

• Usage: hostname

• Explanation: Displays or sets the system’s hostname.

  Example:

  $ hostname

🧪 Linux Command Line Practice Test

1. ✅ Check the hostname of the system

Q: What command is used to check the hostname of the current system?

hostname

2. 🕒 Check the current time of the system

Q: Which command displays the system’s current date and time?

date

3. 🖥️ Change the hostname

Q: What command would you use to change the system hostname to linuxlab?

sudo hostnamectl set-hostname linuxlab

4. 📁 Directory navigation

Q: Create a directory called practice, move into it, and list at least 3 cd commands to navigate.

mkdir practice
cd practice
cd ..
cd -
cd ~

5. 📄 Create and edit a file

Q: How do you create a file called notes.txt, add content using cat, and then edit it using vi?

touch notes.txt
cat > notes.txt
# (Type content and press Ctrl+D)
vi notes.txt
# (Press 'i' to insert, Esc to exit insert, ':wq' to save and exit)

6. 💾 Check available memory

Q: Which command shows you memory usage in human-readable format?

free -h

7. 💽 Check disk and CPU info

Q: How can you check the disk space and number of CPU cores?

df -h      # Disk space
nproc      # Number of CPU cores
lscpu      # Detailed CPU info

8. 🗑️ Practice rm command

Q: What is the difference between rm file.txt and rm -rvf dir/?

• rm file.txt removes a single file.
• rm -rvf dir/ forcefully and recursively removes the directory dir and all its contents without confirmation.

9. 📋 Practice cp command

Q: Copy a.txt to b.txt, and recursively copy a folder dir1 to dir2.

cp a.txt b.txt
cp -rvf dir1/ dir2/

10. 🔁 Move and rename files

Q: How do you move temp.txt to /tmp and rename data.txt to archive.txt?

mv temp.txt /tmp/
mv data.txt archive.txt

11. 📂 Check file systems

Q: What command lists the file systems and their types?

df -T
lsblk -f
mount | column -t

🧪 Linux Command Line Practice Test (Relearn Theme)

1. ✅ Check the hostname of the system

2. 🕒 Check the current time of the system

3. ✏️ Change the hostname of the system

4. 📁 Create a directory and practice cd commands

5. 📝 Create a file with touch, add contents using cat, and edit with vi

6. 📊 Check memory available

7. 💽 Check disk usage and number of CPUs

8. 🗑️ Practice rm and rm -rvf

9. 📄 Practice cp and cp -rvf

10. 📦 Test mv command

11. 🗃️ Check different file systems available

Lab @1

• Login to a linux and enable password Authentication
• Check the root home directory
• Switch to a different user from root user
• Set the hostname persistently across reboot
• Reboot system
• Shut down vm
• Check for how long system is running ?