In today’s data-driven world, effective disk space management is crucial for maintaining system health and performance. Whether you’re a system administrator managing enterprise servers or a Linux enthusiast working on personal projects, knowing how to monitor, analyze, and optimize disk usage is an invaluable skill. This comprehensive guide explores the most powerful Linux commands for disk space management with practical examples you can implement immediately.
Understanding Your Disk Space
Before diving into specific commands, it’s important to understand your current disk usage. The foundation of disk space management starts with accurate measurements.
Checking Overall Disk Usage
The df (disk free) command provides a snapshot of your disk space usage across all mounted filesystems:
df -h
Real Example Output:
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 458G 279G 156G 65% /
/dev/sdb1 1.8T 1.2T 548G 69% /data
tmpfs 16G 24M 16G 1% /tmp
The -h flag presents the results in human-readable format (GB, MB), making it easier to interpret at a glance.
For a more focused view of specific filesystem types:
df -hT | grep -v tmpfs
Real Example Output:
Filesystem Type Size Used Avail Use% Mounted on
/dev/sda1 ext4 458G 279G 156G 65% /
/dev/sdb1 xfs 1.8T 1.2T 548G 69% /data
This command filters out temporary filesystems, showing only permanent storage devices.
Essential Commands for Disk Space Analysis
The Versatile du Command
The du (disk usage) command is your go-to tool for analyzing specific directories:
du -sh /home/user
Real Example Output:
24G /home/user
To see the breakdown of disk usage within a directory:
du -h --max-depth=1 /var | sort -hr
Real Example Output:
14G /var
9.2G /var/log
2.7G /var/cache
1.5G /var/lib
422M /var/tmp
124K /var/spool
This helps identify which subdirectories are consuming the most space.
Getting File Sizes in Gigabytes
For larger systems, viewing file sizes in gigabytes can be more practical:
du -h --block-size=G /var/log | sort -rn
Real Example Output:
9G /var/log
5G /var/log/journal
2G /var/log/apache2
1G /var/log/mysql
Finding and Managing Large Files
Large files are often the culprits behind disk space issues. Here’s how to track them down:
find /home -type f -size +100M -exec du -h {} \; | sort -rh
Real Example Output:
2.4G /home/user/Videos/conference-recording.mp4
1.2G /home/user/Downloads/ubuntu-22.04.iso
950M /home/user/Documents/database-backup.sql
To find large files and see their types:
find / -type f -size +500M -exec ls -lh {} \; 2>/dev/null | awk '{print $5, $9}' | sort -rh
Real Example Output:
4.2G /var/lib/mysql/database/table.ibd
3.7G /home/user/Videos/company-event.mp4
2.1G /opt/application/logs/debug.log
Identifying Recently Modified Large Files
To find large files that were recently modified (potential culprits for sudden disk space consumption):
find / -type f -size +100M -mtime -7 -exec ls -lh {} \; 2>/dev/null
Real Example Output:
-rw-r----- 1 mysql mysql 2.3G Mar 24 03:14 /var/lib/mysql/database/table.ibd
-rw-r--r-- 1 user user 1.5G Mar 25 14:22 /home/user/Downloads/backup.tar.gz
This command finds files larger than 100MB that were modified in the last 7 days.
Identifying Disk Space Hogs by Directory
To get a comprehensive view of directory sizes:
for dir in /*; do if [ -d "$dir" ]; then du -sh "$dir"; fi; done | sort -hr
Real Example Output:
240G /home
112G /var
45G /opt
28G /usr
5.2G /root
1.2G /etc
For a visual representation of disk usage, consider installing and using ncdu:
sudo apt-get install ncdu # Debian/Ubuntu
sudo dnf install ncdu # Fedora/RHEL
ncdu /
This interactive tool allows you to navigate through your filesystem and see disk usage in a more intuitive way.
Managing Disk Space in Real-time
Cleaning Package Caches
On Debian/Ubuntu systems:
sudo apt-get clean
sudo apt-get autoremove
On Fedora/RHEL systems:
sudo dnf clean all
sudo dnf autoremove
Clearing Log Files Safely
To truncate large log files without deleting them (preserving file permissions and processes):
sudo truncate -s 0 /var/log/large-log-file.log
For a more systematic approach to log rotation:
sudo logrotate -f /etc/logrotate.conf
Finding and Removing Duplicate Files
Install and use fdupes to identify duplicate files:
sudo apt-get install fdupes # Debian/Ubuntu
sudo dnf install fdupes # Fedora/RHEL
fdupes -r /home/user
Real Example Output:
/home/user/Documents/report.pdf
/home/user/Downloads/report-copy.pdf
/home/user/Pictures/vacation/beach.jpg
/home/user/Pictures/vacation/backup/beach.jpg
/home/user/Pictures/vacation/backup2/beach.jpg
To delete duplicates interactively:
fdupes -rd /home/user
Automating Disk Space Maintenance
Creating a Simple Disk Space Monitor Script
#!/bin/bash
# disk-monitor.sh - Monitor disk space and send alerts
THRESHOLD=90
EMAIL="[email protected]"
USAGE=$(df -h | grep '/dev/sda1' | awk '{print $5}' | cut -d'%' -f1)
if [ "$USAGE" -gt "$THRESHOLD" ]; then
echo "ALERT: Disk space usage is at $USAGE% on $(hostname)" |
mail -s "Disk Space Alert" $EMAIL
fi
Add this to your crontab to run daily:
0 9 * * * /path/to/disk-monitor.sh
Setting Up Automatic Log Rotation
Create or modify log rotation configuration:
sudo nano /etc/logrotate.d/custom-app
Add this configuration:
/var/log/custom-app/*.log {
daily
rotate 7
compress
delaycompress
missingok
notifempty
create 0640 www-data www-data
}
Advanced Techniques for System Administrators
Using iotop to Monitor Disk I/O
Install and use iotop to identify processes with high disk activity:
sudo apt-get install iotop # Debian/Ubuntu
sudo dnf install iotop # Fedora/RHEL
sudo iotop
Managing Docker Disk Space
For systems running Docker:
# Check Docker disk usage
docker system df
# Clean up unused Docker resources
docker system prune -a
Real Example Output:
TYPE TOTAL ACTIVE SIZE RECLAIMABLE
Images 15 10 3.5GB 1.2GB (34%)
Containers 5 3 256MB 86.5MB (33%)
Local Volumes 12 8 5.7GB 2.1GB (36%)
LVM Resizing for Flexible Space Management
Extend a logical volume to use more space:
# Add 10GB to the logical volume
sudo lvextend -L +10G /dev/vg0/lv_home
# Resize the filesystem to use the new space
sudo resize2fs /dev/vg0/lv_home
Troubleshooting Common Disk Space Issues
When df and du Disagree
If df shows less free space than expected based on du results:
# Find open but deleted files
sudo lsof | grep -E '(deleted)'
Real Example Output:
mysqld 1234 mysql 12u REG 253,0 5242880 4194302 /var/lib/mysql/ib_logfile0 (deleted)
These files are still held open by running processes but have been deleted, causing the discrepancy.
Dealing with Disk Full Errors
Quick emergency steps when facing “No space left on device” errors:
# Find and remove old temporary files
sudo find /tmp -type f -atime +10 -delete
# Clean journal logs (for systemd systems)
sudo journalctl --vacuum-time=3d
Best Practices for Disk Space Management
- Regular Monitoring: Set up automated alerts before space becomes critical
- Proactive Log Management: Configure proper log rotation for all applications
- Use Quotas: Implement user and group quotas to prevent space abuse
- Strategic Partitioning: Separate system and data partitions to prevent system failures due to filled disks
- Document Growth Patterns: Keep records of disk space usage trends to predict future needs
To implement user quotas:
# Enable quotas on filesystem
sudo apt-get install quota
sudo nano /etc/fstab
# Add usrquota to the mount options
# After remounting, initialize quotas
sudo quotacheck -cum /home
sudo quotaon /home
# Set quota for a user (100GB soft limit, 110GB hard limit)
sudo setquota -u username 102400000 112640000 0 0 /home
Conclusion
Effective disk space management is an ongoing process that requires vigilance, the right tools, and proper planning. By mastering the commands and techniques described in this guide, you’ll be well-equipped to handle disk space challenges proactively before they impact your systems and users.
Remember that the best approach combines automated monitoring, regular maintenance, and having a solid understanding of your specific environment’s disk usage patterns. With these skills, you can ensure your Linux systems remain healthy and performant even as data volumes continue to grow.
Start implementing these practices today, and transform disk space management from a reactive emergency task to a smooth, routine aspect of your system administration.