Mastering Ncdu: A Comprehensive Guide

Nov 8, 2025 by Admin 38 views

ncdu is a powerful, disk usage analyzer that helps you identify which files and directories are consuming the most space on your system. Unlike graphical tools, ncdu operates in the terminal, making it incredibly efficient and versatile, especially for remote servers or systems without a graphical interface. This comprehensive guide will walk you through everything you need to know to effectively use ncdu, from installation to advanced usage scenarios. So, if you're tired of guessing where all your disk space went, stick around, and let's dive into the world of ncdu!

What is ncdu?

At its core, ncdu (NCurses Disk Usage) is a command-line utility that scans your file system and presents a navigable interface showing directory sizes. The beauty of ncdu lies in its simplicity and speed. It quickly indexes files and directories, allowing you to drill down into specific areas to pinpoint space hogs. For system administrators and developers, ncdu is an invaluable tool for maintaining optimal disk usage, especially on servers where graphical interfaces are unavailable or impractical.

Why should you care about disk usage analysis? Well, running out of disk space can lead to a multitude of problems, including system crashes, application failures, and data loss. Regularly monitoring disk usage and identifying large, unnecessary files or directories can prevent these issues and keep your system running smoothly. Ncdu provides a straightforward way to accomplish this, even for those who are not command-line gurus.

Think of ncdu as your friendly neighborhood disk detective. It efficiently investigates your file system, uncovers hidden space wasters, and presents the information in an easy-to-understand format. Whether you're a seasoned Linux veteran or a newcomer to the command line, ncdu is a tool that can significantly improve your system administration toolkit.

Installation

Before you can start using ncdu, you'll need to install it. The installation process is straightforward and typically involves using your system's package manager. Here's how to install ncdu on various operating systems:

Debian/Ubuntu:

sudo apt update
sudo apt install ncdu

This command first updates the package lists and then installs the ncdu package. Once the installation is complete, you can run ncdu from your terminal.

CentOS/RHEL/Fedora:

sudo yum install ncdu

Alternatively, if you're using Fedora or a newer version of CentOS/RHEL with dnf, you can use:

sudo dnf install ncdu

These commands install ncdu from the system's default repositories. Ensure your system is up-to-date before running the installation.

macOS:

If you're on macOS, you can use Homebrew to install ncdu:

brew install ncdu

If you don't have Homebrew installed, you can get it from brew.sh. Homebrew simplifies the installation of many command-line tools on macOS.

Windows:

While ncdu is primarily a Linux/Unix tool, you can use it on Windows via the Windows Subsystem for Linux (WSL). First, enable WSL and install a Linux distribution (like Ubuntu) from the Microsoft Store. Then, follow the Debian/Ubuntu installation instructions above.

Once installed, verify the installation by running ncdu --version in your terminal. This will display the installed version of ncdu, confirming that the installation was successful. If you encounter any issues during installation, consult your system's package manager documentation or search online for solutions specific to your operating system. With ncdu successfully installed, you're ready to start analyzing your disk usage!

Basic Usage

Now that you have ncdu installed, let's explore the basic commands and options to get you started. The simplest way to use ncdu is to run it without any arguments. This will scan the current directory and display the disk usage information.

Scanning the Current Directory:

To scan the current directory, simply type ncdu in your terminal and press Enter:

ncdu

This will initiate a scan of the current directory and its subdirectories. Once the scan is complete, ncdu will display an interactive interface showing the size of each directory and file. You can then navigate through the directories using the arrow keys.

Scanning a Specific Directory:

To scan a specific directory, provide the directory path as an argument to the ncdu command:

ncdu /path/to/directory

Replace /path/to/directory with the actual path to the directory you want to scan. For example, to scan the /var/log directory, you would use:

ncdu /var/log

This is particularly useful when you want to focus on a specific area of your file system, such as a user's home directory or a log directory.

Navigating the Interface:

Once ncdu has scanned the directory, you can navigate the interface using the following keys:

Up/Down Arrow Keys: Move up and down the list of files and directories.
Enter: Open a directory to view its contents.
Left Arrow Key or h: Go back to the parent directory.
n: Sort by name (alphabetical order).
s: Sort by size.
C: Sort by items (number of files/directories).
d: Delete the selected file or directory (use with caution!).
i: Show information about the selected file or directory.
q: Quit ncdu.

The interface displays the size of each file and directory, as well as a graphical representation of its relative size. This allows you to quickly identify the largest consumers of disk space. The interactive nature of ncdu makes it easy to drill down into specific areas and pinpoint the exact files or directories that are taking up the most space.

Advanced Usage

While the basic usage of ncdu is straightforward, its advanced features provide even more flexibility and control. Let's explore some advanced options that can help you fine-tune your disk usage analysis.

Excluding Files and Directories:

Sometimes, you may want to exclude certain files or directories from the scan. This can be useful for ignoring temporary files, cache directories, or other areas that you know are not relevant to your analysis. You can use the -x option to exclude directories on a different filesystem and --exclude to specify patterns of files/directories to exclude.

ncdu --exclude /path/to/exclude /path/to/scan

For example, to exclude the /tmp directory from the scan, you would use:

ncdu --exclude /tmp /

You can also use wildcards to exclude multiple files or directories based on a pattern. For instance, to exclude all files ending with .log, you can use:

ncdu --exclude '*.log' /

Read-Only Mode:

To prevent accidental deletions, you can run ncdu in read-only mode using the -r option:

ncdu -r /path/to/scan

In read-only mode, the d key for deleting files and directories will be disabled. This is a good practice, especially when running ncdu on critical systems.

Exporting and Importing Scans:

Ncdu allows you to export scan results to a file, which can then be imported later. This is useful for analyzing disk usage on a remote server without a graphical interface, or for comparing disk usage over time. To export a scan, use the -o option:

ncdu -o scan.txt /path/to/scan

This will save the scan results to the scan.txt file. To import the scan later, use the -i option:

ncdu -i scan.txt

Adjusting Display Options:

Ncdu provides several options to customize the display. For example, you can use the -g option to show sizes in human-readable format (e.g., KB, MB, GB):

ncdu -g /path/to/scan

This makes it easier to interpret the sizes of files and directories. You can also use the -B option to specify the block size:

ncdu -B 4096 /path/to/scan

Adjusting the block size can affect the accuracy of the disk usage calculation, especially on systems with large files or directories.

Combining Options:

You can combine multiple options to create powerful and customized scans. For example, to exclude the /tmp directory, show sizes in human-readable format, and run in read-only mode, you can use:

ncdu -r -g --exclude /tmp /

Experiment with different combinations of options to find the settings that work best for your specific needs.

Practical Examples

To illustrate the power of ncdu, let's look at some practical examples of how you can use it to solve common disk usage problems.

Finding Large Files in Your Home Directory:

To find the largest files in your home directory, simply run:

ncdu ~/

Navigate the interface to identify the files and directories that are consuming the most space. You can then decide whether to delete, move, or compress these files to free up disk space.

Analyzing Log Files:

Log files can often grow to be quite large, especially on busy servers. To analyze the size of log files in the /var/log directory, use:

ncdu /var/log

Sort by size using the s key to quickly identify the largest log files. You can then investigate these files to determine if they can be rotated, compressed, or deleted.

Identifying Space Hogs in a Web Server Directory:

If you're managing a web server, you may want to analyze the disk usage in the web server's document root directory. For example, if your document root is /var/www/html, you can use:

ncdu /var/www/html

This can help you identify large images, videos, or other files that are consuming excessive disk space. You can then optimize these files or move them to a different storage location.

Monitoring Disk Usage Over Time:

To monitor disk usage over time, you can export scan results to a file and compare them later. First, export the initial scan:

ncdu -o initial_scan.txt /

Then, after some time has passed, export another scan:

ncdu -o current_scan.txt /

You can then use a tool like diff to compare the two scan files and identify changes in disk usage:

diff initial_scan.txt current_scan.txt

This can help you track down which files or directories have grown the most over time.

Tips and Tricks

Here are some additional tips and tricks to help you get the most out of ncdu:

Use -x to stay on one filesystem: When scanning a directory, the -x option ensures that ncdu only scans files and directories on the same filesystem. This is useful for avoiding scanning mounted network shares or other filesystems that may be irrelevant to your analysis.
Regularly clean up temporary files: Temporary files can accumulate over time and consume significant disk space. Use ncdu to identify and remove unnecessary temporary files in directories like /tmp.
Compress large files: If you have large files that you don't need to access frequently, consider compressing them using tools like gzip or bzip2. This can significantly reduce their disk space usage.
Automate disk usage analysis: You can create a cron job to automatically run ncdu and generate reports on a regular basis. This can help you proactively monitor disk usage and identify potential problems before they cause issues.
Be careful when deleting files: Always double-check before deleting files or directories using ncdu. Once a file is deleted, it may be difficult or impossible to recover.

Conclusion

ncdu is an indispensable tool for anyone who needs to manage disk space efficiently. Its simple interface, powerful features, and versatility make it a must-have for system administrators, developers, and anyone who wants to keep their systems running smoothly. By mastering the techniques outlined in this guide, you can quickly identify space hogs, optimize disk usage, and prevent potential problems. So, go ahead, give ncdu a try, and take control of your disk space today!