How to Check Memory Usage on Linux: Simple Commands

To check memory usage on Linux, use the free command to see total, used, and available memory. You can also use top or vmstat for real-time memory stats and detailed system info.

Syntax

The basic commands to check memory usage are:

• free -h: Shows memory usage in human-readable format.
• top: Displays real-time system processes and memory usage.
• vmstat 1 5: Shows memory and system stats every second for 5 times.

bash

free -h

top

vmstat 1 5

Example

This example uses free -h to display memory usage in a clear, readable way. It shows total, used, free, shared, buff/cache, and available memory.

bash

free -h

Output

              total        used        free      shared  buff/cache   available
Mem:           7.7Gi       2.1Gi       3.2Gi       150Mi       2.4Gi       5.0Gi
Swap:          2.0Gi          0B       2.0Gi

Common Pitfalls

Many users mistake used memory as the only important value, but Linux uses free memory for cache and buffers to speed up the system. The available memory is a better indicator of how much memory is free for new applications.

Also, running top without understanding its columns can confuse beginners. Focus on the RES (resident memory) column for actual memory used by processes.

bash

free

# Wrong: Assuming 'used' means memory is low
# Right: Check 'available' for free memory

Quick Reference

Command	Description
free -h	Show memory usage in human-readable format
top	Display real-time processes and memory usage
vmstat 1 5	Show memory and system stats every second for 5 times
cat /proc/meminfo	Detailed memory info from system file

Key Takeaways

Use free -h for a quick, clear memory usage summary.

Check the available memory, not just used, to understand free memory.

Use top for real-time memory and process monitoring.

Avoid confusing cache/buffer memory with used memory.

Use vmstat for detailed periodic memory stats.