Disk Usage & File System Monitoring in Red Hat Linux

Welcome to Day 20 of the 30 Days of Linux Challenge!

Today I focused on disk usage and file system monitoring — a must-have skill for preventing crashes, outages, and silent failures in Linux systems.

If you've ever had a system fail because /var or /tmp filled up, you'll know why this topic is crucial.

📚 Table of Contents

• Why Disk Monitoring Matters
• Check Disk Space with df
• Analyze Directory Size with du
• View Block Devices with lsblk
• Mounted File Systems with mount
• Find Large Files
• Clean-Up Tips
• Try It Yourself
• Real-World Use Cases
• Why This Matters

Why Disk Monitoring Matters

Linux won't always alert you when:

• Disk space is about to run out
• Backups are failing due to full storage
• Logs are overwhelming /var

Without monitoring:

• Applications can crash
• Services may silently fail
• You risk total system instability

Check Disk Space with df

df -h

Flag Meaning
-h Human-readable (GB, MB, etc.)

Sample output:

Filesystem Size Used Avail Use% Mounted on
/dev/sda3 100G 75G 25G 75% /
tmpfs 16G 0 16G 0% /dev/shm

Analyze Directory Size with du

du -sh /var/log

Break down large folders:

du -h --max-depth=1 /home

Useful for finding:

• Disk-heavy users
• Log folders gone wild
• Forgotten downloads

View Block Devices with lsblk

lsblk

Visualizes:

• Disks
• Partitions
• Mount points
• LVM volumes

Example:

NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 100G 0 disk
├─sda1 8:1 0 1G 0 part /boot
└─sda2 8:2 0 99G 0 part /

Mounted File Systems with mount

mount | column -t

See:

• Devices
• Mount paths
• File system types

Alternative:

findmnt

Find Large Files

All files over 1 GB

find / -type f -size +1G 2>/dev/null

Sort by size:
ls -lhS /var/log

Interactive viewer:

sudo dnf install ncdu
sudo ncdu /

Clean-Up Tips

Clear package cache:

sudo dnf clean all

Truncate log files:
sudo truncate -s 0 /var/log/messages

Clear systemd journal logs:
sudo journalctl --vacuum-time=7d

Try It Yourself

-Check overall disk usage
df -h

-Identify large folders
du -h --max-depth=1 /var

-List block devices
lsblk

-Search large files
find / -type f -size +500M

-Check mount points
mount | column -t

Real-World Use Cases

Why This Matters

Running out of disk space can:

• Break services and applications
• Cause data loss
• Crash entire systems
• Monitoring and cleaning storage isn’t optional — it’s survival.