Essential Guide to the Df Command: Check Disk Space in Linux

Are you struggling to keep track of your Linux system's disk space? The df command is your go-to solution! This powerful utility helps you monitor disk usage effortlessly. In this comprehensive guide, we'll explore the df command, its options, and how to use it like a pro.

What is the Df Command?

The df command, short for "disk free," is a built-in Linux tool that reports file system disk space usage. It's an essential utility for both system administrators and regular users.

Basic Usage of Df Command

To get started, open your terminal and type:

df

This command displays a table with information about all mounted file systems, including:

• File system name
• Total size
• Used space
• Available space
• Percentage used
• Mount point

Df Command Options

Let's dive into some useful options to maximize the df command's potential:

1. Human-Readable Format (-h)

For sizes in a more readable format (KB, MB, GB), use:

df -h

2. Show Inodes (-i)

To check inode usage instead of block usage:

df -i

3. Display Specific File System (-T)

To show the file system type:

df -T

4. Exclude Certain File Systems (-x)

To exclude specific file systems, like tmpfs:

df -x tmpfs

5. Total Summary (-t)

To display a total for all listed file systems:

df -t

Practical Examples

Let's explore some real-world examples to help you master the df command:

Example 1: Check Available Space on Root Partition

df -h /

This command shows the disk usage of your root partition in a human-readable format.

Example 2: Display All File Systems, Including Pseudo and Duplicate

df -a

Use this to see all file systems, even those that are usually hidden.

Example 3: Check Disk Usage of a Specific Directory

df -h /home

This command shows the disk usage of the /home directory.

Example 4: Combine Multiple Options

df -hT --total

This command combines human-readable format (-h), file system type display (-T), and a total summary (--total).

Tips for Managing Disk Space

Now that you can check your disk space, here are some tips to manage it effectively:

1. Regularly clean up temporary files and cache
2. Uninstall unused applications
3. Use disk usage analyzers like du or ncdu for detailed breakdowns
4. Set up disk quotas for users to prevent overuse
5. Use compression tools for large files
6. Implement log rotation to manage growing log files
7. Use symbolic links to move large directories to other partitions

Troubleshooting Common Issues

Here are some common problems and solutions when using the df command:

Issue 1: Df Shows 100% Usage, But Space is Available

This can happen due to reserved space for the root user. Try:

df -h --total

to see if there's actually free space available.

Issue 2: Df Output Doesn't Update After Deleting Files

Some processes might still be holding onto deleted files. Try:

sudo lsof | grep deleted

to identify these processes, then restart them.

Advanced Df Usage

For power users, here are some advanced techniques:

Combine Df with Other Commands

Use df with grep to filter results:

df -h | grep /dev/sda

Create a Disk Space Alert Script

Here's a simple bash script to alert you when disk space is low:

#!/bin/bash
THRESHOLD=90
df -h | awk '{print $5 " " $6}' | while read output;
do
  usage=$(echo $output | awk '{print $1}' | cut -d'%' -f1)
  partition=$(echo $output | awk '{print $2}')
  if [ $usage -ge $THRESHOLD ]; then
    echo "WARNING: Partition $partition is ${usage}% full!"
  fi
done

Save this as disk_alert.sh, make it executable with chmod +x disk_alert.sh, and run it periodically using cron.

Monitoring Disk Space Over Time

To track disk space usage trends, you can create a simple logging script:

#!/bin/bash
LOG_FILE="/var/log/disk_usage.log"
DATE=$(date +"%Y-%m-%d %H:%M:%S")
df -h | grep -vE '^Filesystem|tmpfs|cdrom' | awk '{ print $5 " " $1 }' | while read output;
do
  usage=$(echo $output | awk '{print $1}' | cut -d'%' -f1)
  partition=$(echo $output | awk '{print $2}')
  echo "${DATE} - ${partition}: ${usage}%" >> $LOG_FILE
done

Run this script regularly to keep a log of disk usage over time.

Df Command in System Administration

System administrators can leverage the df command in various ways:

1. Capacity Planning: Regularly monitor disk usage to plan for upgrades or additional storage.
2. Troubleshooting: Quickly identify file systems that are running out of space.
3. Performance Optimization: Full disks can lead to system slowdowns. Use df to prevent this.
4. Automated Reporting: Incorporate df output into system health reports.

Df Command Alternatives

While df is powerful, there are other tools you might find useful:

1. du: Estimates file space usage
2. ncdu: NCurses Disk Usage, an interactive version of du
3. pydf: A Python-based version of df with color output
4. dfc: Displays file system space usage using graphs and colors

Conclusion

The df command is an indispensable tool for managing disk space in Linux. By mastering its options and usage, you can easily monitor your system's storage, prevent disk space issues, and keep your Linux machine running smoothly.

Remember to check your disk space regularly, clean up unnecessary files, and use the tips provided to maintain a healthy system. With the knowledge from this guide, you're now equipped to handle disk space management like a pro!

Happy disk space monitoring!