Master the free -h Command: Monitor Memory Usage in Linux

What is the free -h Command?

Picture free -h as your system’s memory gauge, showing how much RAM and swap space is used or available in a human-readable format (e.g., GB, MB). It’s key for diagnosing performance issues.

Why free -h is Essential

Syntax and Options

The free -h command displays memory usage:

free -h
        

Key options:

• -h: Human-readable sizes (e.g., GB, MB).
• -s: Continuous updates (seconds).
• -t: Show total for RAM and swap.
• -w: Wide output with buff/cache split.

Output columns: total, used, free, shared, buff/cache, available.

Real-World Examples

1. Check Memory Usage

View memory status:

free -h
        

Output: Shows RAM and swap (e.g., Mem: 16G 8G 4G 1G 4G).

2. Include Totals

Show combined RAM and swap:

free -h -t
        

Output: Adds a total row for combined memory.

3. Continuous Monitoring

Update every 5 seconds:

free -h -s 5
        

Output: Refreshes memory stats every 5 seconds.

4. Wide Output

Use wide format for detailed buff/cache:

free -h -w
        

Output: Splits buff/cache into separate columns.

5. Check Low Memory

Monitor available memory:

free -h | grep Mem | awk '{print $7}'
        

Output: Shows available memory (e.g., 4G).

Advanced Usage

Elevate free -h with these techniques:

• Scripting Alerts: Use in scripts to warn about low memory.
• Continuous Monitoring: Combine with watch for real-time updates.
• Compare with top: Cross-check memory usage with top.
• Extract Specific Metrics: Use awk to parse available memory.

Example: Alert for low memory:

free -h | grep Mem | awk '$7 < 1G {print "Low memory: " $7}'
        

Pro Tips

Check Available: Focus on available for usable memory.

Monitor Swap: High swap usage may indicate RAM shortages.

Automate: Use watch free -h for continuous monitoring.

Common Mistakes to Avoid

Avoid these pitfalls with free -h:

• Misreading Free: Focus on available, not free, for usable memory.
• Ignoring Swap: High swap usage can slow performance.
• Skipping -h: Use -h for readable units.

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