Chapter 2: Linux Filesystem & Essential Commands

1. Introduction

Every Linux administrator spends a significant amount of time navigating the filesystem. Configuration files, application data, log files, software packages and user documents are all stored within a single, well-defined directory hierarchy. Understanding this structure is one of the most valuable skills for beginners because nearly every command you learn later depends on knowing where files are located.

2. Understanding the Linux Filesystem

Unlike Windows, Linux does not organize storage using drive letters such as C: or D:. Instead, everything begins from a single top-level directory called the root directory (/). Additional disks, USB devices and network filesystems are attached somewhere under this hierarchy through a process called mounting.

                /
      ├── boot
      ├── dev
      ├── etc
      ├── home
      ├── opt
      ├── proc
      ├── root
      ├── tmp
      ├── usr
      └── var
                  

3. Important Linux Directories

4. Absolute vs Relative Paths

An absolute path always starts from /, while a relative path starts from your current working directory.

Absolute: /home/student/Documents/report.txt
Relative: Documents/report.txt

5. The pwd Command

The pwd command prints the current working directory.

$ pwd
/home/student

6. The cd Command

The cd command changes your current directory.

7. Hands-on Practice

1. Navigate to /var.
2. Return to your home directory.
3. Move to the root directory.
4. Use cd - to return.
5. Verify every step using pwd.

9. Creating Directories with mkdir

mkdir project
mkdir logs backup temp
mkdir -p /tmp/demo/test

The -p option creates parent directories automatically if they do not already exist.

10. Creating Files with touch

touch notes.txt
touch file1 file2 file3
touch /tmp/app.log

Besides creating empty files, touch also updates file timestamps.

11. Copying Files with cp

cp file1 file2
cp report.txt /backup/
cp -r project backup_project

12. Moving and Renaming Files with mv

mv old.txt new.txt
mv report.txt /archive/
mv *.log /var/log/archive/

The same command is used both for renaming files and moving them to a different directory.

13. Removing Files with rm

rm file.txt
rm -i file.txt
rm -r directory
rm -rf temp_directory

14. Redirection and Pipes

Shell redirection sends command output to files or other commands instead of the terminal.

The tee command is not a redirection operator. It reads stdin and writes it both to a file and to stdout, which is useful when you want a saved copy and still want to see the output:

ls -l > listing.txt
echo "error" >> app.log
grep ERROR /var/log/syslog 2> errors.txt
df -h | tee disk-report.txt

16. Searching via find and locate

The find command searches directories based on name, type, size, and modifications.

find /etc -name sshd_config
find . -name "*.log"

The locate command searches a prebuilt filename database. On many distributions the database tools come from plocate or the older mlocate package (whichever your distro ships). Update the database with updatedb before relying on locate results.

sudo updatedb
locate sshd_config

17. Hard Links vs Symbolic Links

ln file1 hardlink1
ln -s /etc/ssh/sshd_config sshd_config_link

18. Inspecting Files with stat and file

The stat command displays detailed metadata including permissions, inode, timestamps and ownership. The file command determines the actual file type instead of relying on the filename extension.

$ stat /etc/hostname
  File: /etc/hostname
  Size: 12        	Blocks: 8          IO Block: 4096   regular file
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)

$ file /bin/ls
/bin/ls: ELF 64-bit LSB pie executable, x86-64, ...

19. Disk Usage Commands (df, du)

Use df -h to check free and used space on mounted filesystems. Use du -sh to determine which directories consume the most storage.

$ df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1        50G   32G   16G  67% /

$ du -sh /var/log
248M	/var/log

$ du -sh /var/log/* | sort -h | tail -5
 12M	/var/log/journal
 80M	/var/log/syslog