Monitoring disk space usage is a crucial task for both system administrators and everyday users in a Linux environment. Linux provides several tools that allow users to easily check how much disk space is used and how much is free. This article covers different methods to check disk usage, focusing on the commonly used commands df, du, and ncdu.

df Command: Basic Disk Usage Overview

The df (disk free) command is the most widely used tool for quickly checking available disk space. This tool provides an overview of how much space is used on a disk, how much is free, and which file system is in use.

To display the current disk space usage, you can use the following command:

df -h

The -h flag stands for "human-readable," which formats the output in easily understandable units like MB, GB, or TB. The output will look something like this:

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1        20G   15G  5.0G  75% /

Explanation of the output:

• Filesystem: The name of the file system or disk partition.
• Size: The total size of the disk or partition.
• Used: The amount of space that is currently used.
• Avail: The available free space.
• Use%: The percentage of space used.
• Mounted on: The mount point where the disk is attached in the system.

If you need to check the usage of a specific disk, you can add the disk name as an argument:

df -h /dev/sda1

du Command: Detailed Disk Usage Analysis

While df gives a general overview of total disk usage, the du (disk usage) command is ideal for a more detailed analysis. This is useful for finding out how much space individual directories and files are consuming.

To get a basic overview of the size of directories, use the following command:

du -h /path/to/directory

This command will display the size of all directories and files in the specified path in a human-readable format. If you only want a summary of the directory size, use the -s flag:

du -sh /path/to/directory

This will show just the total size of the directory without listing each file and subdirectory.

ncdu Command: Interactive Disk Usage Analysis

For an interactive and user-friendly way to visualize disk usage, the ncdu (NCurses Disk Usage) tool is highly recommended. This tool provides a text-based interface that makes it easy to find the largest files and directories on your system.

To install ncdu, use your distribution's package manager. For Debian-based distributions, the command would be:

sudo apt install ncdu

Once installed, you can launch the tool with:

ncdu /path/to/directory

This command will scan the directory and display an interactive list of files and folders sorted by size. Navigation is simple, using arrow keys, and you can easily identify and remove large files if necessary.

Checking Inode Usage

Inodes are data structures used by the file system to store metadata about files. If your system runs out of inodes, it may struggle to create new files, even if there is still free disk space. To check inode usage, use the following command:

df -i

This command will show information about how many inodes are used and available on each partition.

Automating Disk Space Monitoring

You can also set up automatic monitoring of disk space usage using cron jobs. These jobs can run commands like df or du at regular intervals and email the output to you. For example, to check disk usage once a day, add the following line to your crontab:

0 0 * * * df -h | mail -s "Disk Status" This email address is being protected from spambots. You need JavaScript enabled to view it.

Managing disk space is essential for maintaining system performance and avoiding downtime in Linux. Tools like df, du, and ncdu provide valuable information about disk status and allow detailed analysis of disk usage. Regular checks of inode usage and setting up automatic monitoring can help prevent potential issues and keep your system running smoothly.