Essential System Administrator Commands in Ubuntu

1. ls – List Directory Contents

The ls command is used to list the contents of a directory. Here are some example usages:

• ls: List files and directories in the current directory.
• ls /path/to/directory: List files and directories in the specified directory.

2. cd – Change Directory

The cd command is used to change the current working directory. Example usage:

• cd /path/to/directory: Change the current directory to the specified directory.

3. pwd – Print Working Directory

The pwd command prints the current working directory. Example usage:

• pwd: Print the current working directory.

4. mkdir – Make Directory

The mkdir command is used to create directories. Example usage:

• mkdir directory_name: Create a directory with the specified name.

5. rm – Remove

The rm command is used to remove files and directories. Example usage:

• rm file_name: Remove the specified file.
• rm -r directory_name: Remove the specified directory and its contents recursively.

6. cp – Copy

The cp command is used to copy files and directories. Example usage:

• cp file1 file2: Copy file1 to file2.
• cp -r directory1 directory2: Copy directory1 and its contents recursively to directory2.

7. mv – Move

The mv command is used to move or rename files and directories. Example usage:

• mv file1 file2: Move file1 to file2 or rename file1 to file2.
• mv file1 /path/to/directory: Move file1 to the specified directory.

8. touch – Create Empty File

The touch command is used to create an empty file or update the timestamp of an existing file. Example usage:

• touch file_name: Create an empty file with the specified name.

9. cat – Concatenate and Display

The cat command is used to concatenate files and display their contents. Example usage:

• cat file1 file2: Concatenate and display the contents of file1 and file2.
• cat file_name: Display the contents of the specified file.

10. nano – Text Editor

The nano command is a simple text editor used for editing files in the terminal. Example usage:

• nano file_name: Open the specified file in the nano text editor.

11. grep – Search

The grep command is used to search for patterns in text files. Example usage:

• grep pattern file_name: Search for the specified pattern in the specified file.
• grep -r pattern directory: Search for the specified pattern recursively in the specified directory.

12. sudo – Superuser Do

The sudo command is used to execute commands with superuser privileges. Example usage:

• sudo command: Execute the specified command with superuser privileges.

13. apt-get – Package Manager

The apt-get command is used to manage packages on Ubuntu. Example usage:

• sudo apt-get update: Update the package lists for available upgrades.
• sudo apt-get install package_name: Install the specified package.
• sudo apt-get remove package_name: Remove the specified package.

14. dpkg – Package Manager

The dpkg command is used to install, remove, and manage individual packages. Example usage:

• sudo dpkg -i package_file.deb: Install the specified package from a .deb file.
• sudo dpkg -r package_name: Remove the specified package.

15. chmod – Change Mode

The chmod command is used to change the permissions of files and directories. Example usage:

• chmod permissions file_name: Change the permissions of the specified file.
• chmod permissions directory_name: Change the permissions of the specified directory.

16. chown – Change Owner

The chown command is used to change the owner of files and directories. Example usage:

• chown new_owner file_name: Change the owner of the specified file.
• chown new_owner:new_group file_name: Change the owner and group of the specified file.

17. tar – Tape Archive

The tar command is used to archive and extract files. Example usage:

• tar -cvf archive_name.tar files: Create a new archive file.
• tar -xvf archive_name.tar: Extract files from an archive.

18. uname – Print System Information

The uname command prints system information. Example usage:

• uname -a: Print all system information.
• uname -r: Print the kernel release.

19. date – Display Date and Time

The date command is used to display the current date and time. Example usage:

• date: Display the current date and time.
• date "+%Y-%m-%d": Display the current date in YYYY-MM-DD format.

20. shutdown – Shutdown or Restart System

The shutdown command is used to shutdown or restart the system. Example usage:

• sudo shutdown now: Shutdown the system immediately.
• sudo shutdown -r now: Restart the system immediately.

21. ps – Process Status

The ps command is used to display information about active processes. Example usage:

• ps: Display information about active processes.
• ps aux | grep process_name: Display information about processes matching the specified name.

22. top – Display System Activity

The top command is used to display real-time system activity. Example usage:

• top: Display real-time system activity.
• top -u username: Display system activity for the specified user.

23. du – Disk Usage

The du command is used to display disk usage. Example usage:

• du: Display disk usage of the current directory.
• du -h: Display disk usage in human-readable format.

24. df – Disk Free

The df command is used to display disk space usage. Example usage:

• df: Display disk space usage of all mounted filesystems.
• df -h: Display disk space usage in human-readable format.

Automatically Mount a Linux Partition at Boot

Step 1: Identify the Partition UUID

Run the following command in the terminal to get the UUID of your partition:

lsblk -f

Example output:

nvme0n1p5 ext4   PhD  f0e5cddf-907a-4670-880e-2ee175bd1588  ...  /media/saurabh/PhD
  

Step 2: Choose a Mount Point

Recommended options:

• /mnt/phd – for system-wide use
• /home/yourname/phd_drive – for personal use

sudo mkdir -p /mnt/phd

Step 3: Add to /etc/fstab

Edit the /etc/fstab file:

sudo nano /etc/fstab

Add the following line at the end:

UUID=f0e5cddf-907a-4670-880e-2ee175bd1588  /mnt/phd  ext4  defaults  0  2

Step 4: Test the Configuration

sudo mount -a

If no errors occur, it's working!

Step 5: Set Ownership (Optional)

Give your user access to the mount point:

sudo chown yourusername:yourusername /mnt/phd

Using /media/saurabh/PhD as Mount Point

You can use it, but it’s not recommended. Issues include:

• May not exist at boot time
• Can conflict with desktop auto-mounters
• May auto-unmount on logout

If you still want to use it:

sudo mkdir -p /media/saurabh/PhD
sudo chown saurabh:saurabh /media/saurabh/PhD
# Add this to /etc/fstab instead:
UUID=f0e5cddf-907a-4670-880e-2ee175bd1588  /media/saurabh/PhD  ext4  defaults  0  2
  

Understanding Symbolic Links in Linux

🔗 What is a Symbolic Link?

A symbolic link (or symlink) is like a shortcut or alias to another file or directory. It allows access to files across different locations without duplicating data.

📂 Example Use Case

You started Jupyter Lab in ~/Downloads, but want to access files in ~/Documents. Create a symlink:

ln -s ~/Documents ~/Downloads/my_docs

This creates a folder my_docs inside Downloads that points to Documents.

📌 How to Create a Symlink

Basic syntax:

ln -s <target_path> <link_name>

Example:

ln -s /home/saurabh/PhD /mnt/phd

✅ Confirm the Link

ls -l

Output:

lrwxrwxrwx 1 saurabh saurabh  12 May 19 11:11 phd -> /home/saurabh/PhD

🛠 Common Options

• -s: create a symbolic (soft) link instead of a hard link
• -f: force overwrite if the link name already exists

📎 Hard Link vs Symbolic Link

• Hard link: another name for the same file (not recommended for directories)
• Symbolic link: points to the file path (can span partitions and directories)

🧹 How to Remove a Symlink

To remove:

rm <link_name>

This only deletes the link, not the original file or directory.

📁 Jupyter Lab Tip

To access ~/PhD in Jupyter Lab started in ~/Downloads:

ln -s ~/PhD ~/Downloads/phd_link

Now Jupyter can access the phd_link as if it were inside Downloads.