du

Overview

The du (disk usage) command displays the amount of disk space used by files and directories. It’s essential for disk space management and finding large files or directories.

Syntax

du [options] [file/directory...]

Common Options

Option Description
-h Human-readable sizes (K, M, G)
-s Summary only (total for each argument)
-a Show all files, not just directories
-c Display grand total
-d depth Maximum depth to display
-x Stay on same filesystem
-L Follow symbolic links
-P Don’t follow symbolic links
-0 End lines with null character
--max-depth=n Limit directory depth
--exclude=pattern Exclude files matching pattern
--time Show modification time

Key Use Cases

  1. Find disk space usage
  2. Identify large directories
  3. Disk cleanup planning
  4. Storage analysis
  5. System monitoring

Examples with Explanations

Example 1: Current Directory Usage

du -h

Shows disk usage of current directory and subdirectories

Example 2: Summary Only

du -sh *

Shows total size of each item in current directory

Example 3: Specific Directory

du -h /var/log

Shows disk usage of /var/log directory

Example 4: Top-level Summary

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

Shows usage of immediate subdirectories only

Finding Large Files/Directories

  1. Largest directories:

    du -h | sort -hr | head -10

  2. Largest files and directories:

    du -ah | sort -hr | head -20

  3. Directories over 1GB:

    du -h | awk '$1 ~ /G/ {print}'

Common Usage Patterns

  1. Quick size check:

    du -sh directory_name

  2. Find space hogs:

    du -h --max-depth=2 / | sort -hr | head -20

  3. Exclude certain files:

    du -h --exclude="*.log" /var

Advanced Usage

  1. Show modification times:

    du -h --time /home/user

  2. Stay on filesystem:

    du -hx /

  3. Include all files:

    du -ah /etc | head -20

Performance Analysis

  • Can be slow on large filesystems
  • I/O intensive operation
  • Memory usage is minimal
  • Use –max-depth to limit scope
  • Consider excluding network mounts

Best Practices

  1. Use human-readable format (-h)
  2. Limit depth for large directories
  3. Exclude temporary files when needed
  4. Use summary mode for quick checks
  5. Combine with sort for analysis

Disk Cleanup Strategies

  1. Find old large files:

    find /home -size +100M -mtime +30 -exec du -h {} \;

  2. Analyze log directories:

    du -h /var/log/* | sort -hr

  3. Check user directories:

    du -sh /home/* | sort -hr

Scripting Applications

  1. Disk usage monitoring:

    #!/bin/bash
THRESHOLD=80
USAGE=$(du -s /home | awk '{print $1}')
TOTAL=$(df /home | awk 'NR==2 {print $2}')
PERCENT=$((USAGE * 100 / TOTAL))

if [ $PERCENT -gt $THRESHOLD ]; then
    echo "Disk usage warning: ${PERCENT}%"
fi

  2. Cleanup automation:

    cleanup_large_files() {
    du -ah /tmp | awk '$1 ~ /[0-9]+G/ {print $2}' | \
    while read file; do
        echo "Large file found: $file"
        # Add cleanup logic
    done
}

Integration Examples

  1. With find for targeted analysis:

    find /var -name "*.log" -exec du -h {} \; | sort -hr

  2. System health check:

    echo "Top 10 largest directories:"
du -h --max-depth=2 / 2>/dev/null | sort -hr | head -10

  3. User quota monitoring:

    for user in $(ls /home); do
    echo "$user: $(du -sh /home/$user 2>/dev/null | cut -f1)"
done

Output Formatting

  1. Custom format with awk:

    du -h | awk '{printf "%-10s %s\n", $1, $2}'

  2. CSV output:

    du -sb * | awk '{printf "%s,%s\n", $1, $2}'

  3. JSON-like format:

    du -sh * | awk '{printf "{\"size\":\"%s\",\"path\":\"%s\"}\n", $1, $2}'

Troubleshooting

  1. Permission denied errors
  2. Slow performance on large directories
  3. Network filesystem timeouts
  4. Symbolic link loops
  5. Filesystem crossing issues

Security Considerations

  1. May reveal directory structure
  2. Can be resource intensive
  3. Consider access permissions
  4. Monitor for unusual disk usage
  5. Protect sensitive directory information