Disk Usage Analysis with du Command

Overview

The du command (disk usage) is a fundamental Unix/Linux utility that displays the disk space used by files and directories. It recursively examines directory trees and reports space consumption, making it an essential tool for system administrators, developers, and users who need to monitor and manage disk space effectively.

Basic Syntax

`bash du [OPTIONS] [FILE/DIRECTORY] `

Core Functionality

The du command calculates and displays the disk usage of files and directories by examining their actual size on disk. Unlike the ls command which shows file sizes, du provides information about how much disk space is actually consumed, including the space used by subdirectories.

Essential Options and Flags

| Option | Long Form | Description | Example | |--------|-----------|-------------|---------| | -h | --human-readable | Display sizes in human readable format (K, M, G) | du -h /home | | -s | --summarize | Display only total for each argument | du -s /var/log | | -a | --all | Show sizes for all files, not just directories | du -a /etc | | -c | --total | Produce a grand total | du -c /home/* | | -d N | --max-depth=N | Limit recursion to N levels | du -d 2 /usr | | -x | --one-file-system | Skip directories on different file systems | du -x / | | -L | --dereference | Follow symbolic links | du -L /usr/bin | | -S | --separate-dirs | Don't include subdirectory sizes | du -S /home | | -k | --kilobytes | Display sizes in kilobytes | du -k /tmp | | -m | --megabytes | Display sizes in megabytes | du -m /var |

Advanced Options

| Option | Long Form | Description | Use Case | |--------|-----------|-------------|----------| | --apparent-size | --apparent-size | Show apparent sizes rather than disk usage | Comparing file sizes vs disk usage | | --exclude=PATTERN | --exclude=PATTERN | Exclude files matching PATTERN | du --exclude="*.log" /var | | --exclude-from=FILE | --exclude-from=FILE | Exclude files listed in FILE | Bulk exclusions from file | | --time | --time | Show time of last modification | du --time /home/user | | --time-style=STYLE | --time-style=STYLE | Show times using given style | du --time --time-style=iso | | -0 | --null | End each output line with NULL | Scripting with special filenames |

Basic Usage Examples

Simple Directory Analysis

`bash

Check current directory usage

Check specific directory

Human-readable format

Output Example: ` 4.0K /var/log/apt 12K /var/log/journal/a1b2c3d4e5f6 16K /var/log/journal 156K /var/log `

Summarized Usage

`bash

Get total size only

Output Example: ` 2.3G /home/username `

All Files and Directories

`bash

Show all files, not just directories

Output Example: ` 4.0K /etc/nginx/nginx.conf 2.0K /etc/nginx/mime.types 1.0K /etc/nginx/fastcgi_params 8.0K /etc/nginx `

Practical Use Cases

1. Finding Large Directories

`bash

Find largest directories in /home

Alternative with depth limit

Notes: - sort -hr sorts in human-readable format in reverse order - head -10 shows top 10 results - -d 1 limits depth to prevent deep recursion

2. Monitoring System Directories

`bash

Check system log usage

Monitor temporary files

Check package cache

Example Output: ` 45M /var/log/journal 12M /var/log/syslog 8.5M /var/log/kern.log 2.1M /var/log/auth.log `

3. Analyzing User Home Directories

`bash

Check all user directories

Detailed analysis of specific user

Advanced Usage Scenarios

Excluding Files and Patterns

`bash

Exclude log files

Exclude multiple patterns

Exclude from file

Cross-Filesystem Analysis

`bash

Stay within single filesystem

Compare with cross-filesystem

Note: The -x option prevents du from crossing filesystem boundaries, useful when you have multiple mounted filesystems.

Time-based Analysis

`bash

Show modification times

Specific time format

Output Example: ` 4.0K 2023-12-15 14:30 /var/log/apt 12K 2023-12-15 15:45 /var/log/alternatives.log `

Combining with Other Commands

Finding Largest Files

`bash

Combine with find for large files

Files larger than 100MB

Real-time Monitoring

`bash

Watch directory growth

Monitor multiple directories

Scripting Examples

`bash #!/bin/bash

Disk usage report script

echo "=== Disk Usage Report ===" echo "Generated: $(date)" echo

echo "Top 10 largest directories in /home:" du -h /home | sort -hr | head -10 echo

echo "System directory usage:" for dir in /var/log /var/cache /tmp /var/tmp; do if [ -d "$dir" ]; then echo "$(du -sh "$dir" | cut -f1): $dir" fi done `

Performance Considerations

Large Directory Trees

`bash

For very large directories, use depth limits

Or exclude problematic subdirectories

Network Filesystems

`bash

Be cautious with network mounts

Specific network filesystem analysis

Output Formatting and Parsing

Machine-Readable Output

`bash

Null-separated output for scripts

Bytes only (no units)

Custom Formatting

`bash

Kilobytes with totals

Apparent size vs disk usage comparison

Troubleshooting Common Issues

Permission Denied Errors

`bash

Run with appropriate privileges

Redirect errors to suppress them

Show errors separately

Symbolic Links

`bash

Default behavior (don't follow symlinks)

Follow symbolic links

Show difference

Sparse Files

`bash

Show apparent size (logical size)

Show actual disk usage

Comparison Table: du vs Other Tools

| Tool | Purpose | Output | Speed | Detail Level | |------|---------|--------|-------|--------------| | du | Directory/file disk usage | Hierarchical listing | Moderate | High | | df | Filesystem usage | Summary by filesystem | Fast | Low | | ls -l | File listing with sizes | File-by-file | Fast | Medium | | ncdu | Interactive disk usage | Curses interface | Slow | Very High | | tree | Directory structure | Tree format | Fast | Structure only |

Environment Variables

| Variable | Description | Example | |----------|-------------|---------| | DU_BLOCK_SIZE | Default block size | export DU_BLOCK_SIZE=1024 | | POSIXLY_CORRECT | POSIX compliance mode | export POSIXLY_CORRECT=1 | | TIME_STYLE | Default time format | export TIME_STYLE=iso |

Best Practices

Regular Monitoring

`bash

Create monitoring alias

Cron job for regular reports

Efficient Usage

`bash

Use depth limits for large filesystems

Combine with other tools effectively

System Administration

`bash

Check for rapid growth

Automated cleanup trigger

Integration with System Monitoring

Log Analysis

`bash

Monitor log growth

Historical comparison

Backup Planning

`bash

Calculate backup sizes

Estimate backup time (assuming 50MB/s)

Security Considerations

Sensitive Directory Analysis

`bash

Careful with sensitive directories

Audit user space usage

Access Control

`bash

Check accessible directories only

The du command is an indispensable tool for disk space management and system administration. Its flexibility in output formatting, depth control, and integration capabilities make it suitable for both interactive use and automated scripting. Understanding its various options and use cases enables efficient disk space monitoring and management across different scenarios, from personal file organization to enterprise system administration.