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Understanding Memory Usage with `free`
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Understanding Memory Usage with the free
Command in Linux
If you’ve ever found yourself wondering how much memory your server or desktop has available, the free
command in Linux is an indispensable tool. It provides a clear snapshot of the system's memory usage, including RAM and swap space. Understanding the output of the free
command can help you monitor your system’s health and make informed decisions about resource allocation. In this article, we'll break down how to use the free
command and interpret its output effectively.
What is the free
Command?
The free
command is a terminal-based tool in Unix-like operating systems such as Linux. It displays the total amount of free and used physical memory (RAM) and swap space on your system. This command can also show how much of the RAM is being utilized by the kernel for caching.
How to Use the free
Command
Using the free
command is straightforward. Open your terminal, and simply type free
. By default, the output is shown in kilobytes. You can make the free
command output more readable by using the -h
option, which will display the values in human-readable formats (e.g., KB, MB, GB).
free -h
Interpreting the free
Command Output
When you run the free
command, it typically displays several columns. Here's what each column represents:
total: indicates the total amount of memory installed on your system.
used: shows the amount of memory currently being used.
free: displays the amount of memory that is not being used at all.
shared: indicates memory used (mostly) by tmpfs (temporary file storage space).
buff/cache: shows memory used by the kernel buffers and cache.
available: estimates how much memory is available for starting new applications, without swapping.
An example output might look like this:
total used free shared buff/cache available
Mem: 16G 5.3G 580M 1.1G 10G 9.4G
Swap: 2.0G 256M 1.7G
Key Takeaways
Used vs Free: 'Used' memory includes memory used by programs and the system, whereas 'Free' memory is completely unused and ready for programs that might need it.
Buffer and Cache: Linux uses available memory for buffers and caching to speed up the system. This memory can be reclaimed if an application needs it. Hence, the 'Used' memory can seem high, but a lot of it could be in 'buff/cache'.
Available Memory: This is a crucial metric as it gives a more realistic picture of what is actually available for new applications.
Why is Monitoring Memory Important?
Monitoring memory usage is key to ensuring that your Linux system performs well. High memory utilization could mean that your applications are being slowed down, which could potentially cause system hangs or crashes if all memory and swap space are exhausted.
Tools and Tips for Memory Management
Watch and vmstat: These are utilities for monitoring your system's performance in real-time.
Check for memory leaks: Occasionally, applications may have memory leaks. If you notice an application is continually increasing its memory usage, it might need a deeper look.
Optimise your applications: Sometimes, tuning the memory usage settings of certain applications can prevent excessive memory consumption.
Understanding the free
command and how to interpret its outputs can significantly help in managing and troubleshooting Linux systems. By keeping a close eye on the health of your system's memory, you can ensure smooth operations and efficient performance. Whether you're a system administrator, a developer, or just a Linux enthusiast, mastering this tool is an invaluable skill in your toolkit.