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Free Command in Linux
The free command is one of the most essential Linux system administration tools used to display memory usage information. It provides real-time statistics about physical RAM, swap space, buffers, and cache usage, making it invaluable for system monitoring and troubleshooting memory-related issues.
What is the Free Command?
The free command displays the total amount of free and used physical memory and swap space in the system, as well as the buffers and cache used by the kernel. It reads information from /proc/meminfo and presents it in a human-readable tabular format.
Syntax
free [options]
Key Options
| Option | Description | Example |
|---|---|---|
-b |
Display output in bytes | free -b |
-k |
Display output in kilobytes (default) | free -k |
-m |
Display output in megabytes | free -m |
-g |
Display output in gigabytes | free -g |
-h |
Human-readable format (auto-scales units) | free -h |
-t |
Display totals row | free -t |
-s <interval> |
Update every N seconds | free -s 5 |
Understanding the Output
The output contains three main rows
Mem Physical RAM usage statistics
Swap Virtual memory (swap space) usage
Available Memory available for starting new applications (modern systems)
Examples
Basic Usage
free
total used free shared buff/cache available
Mem: 2048000 1024000 512000 8000 512000 1536000
Swap: 1048576 0 1048576
Human-Readable Format
free -h
total used free shared buff/cache available
Mem: 2.0G 1.0G 500M 8.0M 500M 1.5G
Swap: 1.0G 0B 1.0G
Display in Megabytes with Totals
free -mt
total used free shared buff/cache available
Mem: 2000 1000 500 8 500 1500
Swap: 1024 0 1024
Total: 3024 1000 1524
Continuous Monitoring
free -h -s 3
This command updates the memory information every 3 seconds, useful for monitoring memory usage in real-time.
Key Fields Explained
total Total installed memory
used Memory currently in use by processes
free Completely unused memory
shared Memory used by tmpfs filesystems
buff/cache Memory used for buffers and cache
available Memory available for new applications without swapping
Common Use Cases
System monitoring Quick memory health check
Performance tuning Identifying memory bottlenecks
Script automation Memory threshold alerts
Troubleshooting Diagnosing out-of-memory issues
Conclusion
The free command is an indispensable tool for Linux system administrators and users who need to monitor memory usage. Its simple syntax and comprehensive output make it perfect for both quick checks and continuous monitoring. Understanding memory statistics helps optimize system performance and prevent memory-related issues.
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