Efficient memory management is crucial for Linux system administrators, especially when working with virtual machines (VMs) or servers. On Linux, understanding the difference between free memory and available memory is key to optimizing system performance.
This guide explains how Linux uses memory, how to interpret the free command output, and why “unused” memory is not necessarily wasted.
How Linux Handles Memory
Linux treats free memory as an opportunity to improve system performance. The kernel dynamically allocates unused memory to buffers and caches, which store frequently accessed data. By doing so, Linux ensures faster data access and better overall efficiency.
Unused RAM is not actively utilized by processes, but it is leveraged by the kernel for temporary storage, improving system responsiveness.
Using the free Command to Monitor Memory
To check memory usage on a Linux system, use the free command-line utility. This tool helps differentiate between free and available memory.
Run the following command:
free -m
Here’s an example output of the free command:
total used free shared buff/cache available
Mem: 63886 57123 1307 123 5456 6222
Breaking Down the Output
The free command provides several important metrics. Here’s what each column means:
- Total: The total installed memory (RAM) on your system.
- Used: Memory currently being utilized by processes, including memory allocated to buffers and caches.
- Free: Unused memory that is not allocated to any process or buffer.
- Shared: Memory shared by
tmpfs(temporary file systems). - Buff/Cache: Memory used by buffers and caches to store frequently accessed data.
- Available: An estimate of memory available for starting new applications without swapping.
Key Difference: Free vs Available Memory
- Free Memory: Represents memory not allocated to any process or buffer. While this memory is technically “unused,” it is considered wasted in Linux because it is not actively contributing to system performance.
- Available Memory: Includes free memory plus memory allocated to buffers and caches that can be freed when needed. This is a more accurate representation of how much memory is ready for new processes.
Memory Calculation Formula
To calculate memory usage:
Used Memory = Total - (Free + Buffers + Cache)
The available memory column is calculated by summing the free memory and portions of the buffers and caches that can be released immediately.
Summary
Unused RAM is not wasted RAM on Linux systems. Instead, the kernel uses it to store buffers and caches, improving system efficiency. The available memory metric provides a realistic estimate of how much memory is ready for new applications or processes.
By understanding the output of the free command, system administrators can better manage resources and optimize performance.
Practical Example
If you’re running a database server or any high-memory workload, monitoring the available memory is critical to ensure applications have enough resources to run efficiently.
For example:
free -m
If the available memory drops below a certain threshold, you may need to investigate memory usage by processes or adjust system configurations.
Helpful Resources
For more detailed insights into memory management, visit the following resources: