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How To Interpret the Output of ‘free -m’ Command for Memory Usage

Ubuntu 13

In the world of Linux, understanding your system’s memory usage is crucial for monitoring system performance and troubleshooting issues. One of the most common commands for this purpose is free -m. In this article, we will delve into the interpretation of this command’s output.

Quick Answer

The ‘free -m’ command is used to check the memory usage in a Linux system. The output of this command provides information about the total memory, used memory, free memory, shared memory, buffers/cache, available memory, and swap memory. Understanding this output is crucial for monitoring system performance and troubleshooting memory-related issues.

Introduction to the ‘free -m’ Command

The free command in Linux is used to check the amount of free and used memory in the system. The -m option displays the information in megabytes. This command is beneficial when you want to have a quick overview of your system’s memory usage.

free -m

Understanding the Output

When you run the free -m command, you will typically see an output similar to the following:

 total used free shared buff/cache available
Mem: 595 482 112 0 63 501
-/+ buffers/cache: 93 501
Swap: 1023 0 1023

This output can be broken down into several parts.

Total Memory

The ‘total’ column shows the total physical memory available on the system. In this case, it is 595 MB.

Used Memory

The ‘used’ column can be a bit misleading. It shows the total amount of memory used by the system, which includes memory used by the kernel for caching and buffers. In this example, it’s 482 MB.

Free Memory

The ‘free’ column shows the amount of memory that is currently not used by anything, which is 112 MB in this case.

Shared Memory

The ‘shared’ column shows the memory used by tmpfs (temporary file storage in RAM).

Buffers/Cache

The ‘buff/cache’ column shows the memory used by the kernel for buffers and cache, which in this case is 63 MB. This memory can be freed up by the system when necessary.

Available Memory

The ‘available’ column shows how much memory is available for starting new applications, without swapping. Unlike the ‘free’ column, this field takes into account page cache and also that not all reclaimable memory slabs will be reclaimed due to items being in use.

The Second Line: ‘-/+ buffers/cache’

This line provides a more accurate representation of the memory usage on your system by showing the amount of memory actually used by processes (93 MB) and the amount of memory free for use by applications (501 MB).

Swap Memory

The last line shows the total, used, and free swap memory. Swap is the space on the hard disk that is used when the physical memory (RAM) is full. If the system needs more memory resources and the RAM is full, inactive pages in memory are moved to the swap space.

Conclusion

Understanding the output of the free -m command is essential for effectively monitoring and managing your system’s memory usage. Remember, the memory used for buffers and cache is not wasted — it’s being put to work to help your system run more efficiently. However, if needed, it can be freed up and used by applications.

For more information about the free command and its options, you can check the manual pages by running man free in your terminal.

What is the purpose of the `free -m` command?

The free -m command is used to check the amount of free and used memory in a Linux system. It provides an overview of the system’s memory usage in megabytes.

How do I interpret the “used” column in the `free -m` output?

The "used" column in the free -m output represents the total amount of memory used by the system, including memory used by the kernel for caching and buffers.

What does the “free” column indicate in the `free -m` output?

The "free" column shows the amount of memory that is currently not used by anything in the system.

What does the “buff/cache” column represent in the `free -m` output?

The "buff/cache" column in the free -m output shows the memory used by the kernel for buffers and cache. This memory can be freed up by the system when necessary.

How is the “available” memory different from the “free” memory in the `free -m` output?

The "available" memory in the free -m output represents how much memory is available for starting new applications without swapping. It takes into account page cache and the fact that not all reclaimable memory slabs will be reclaimed due to items being in use. The "free" memory, on the other hand, only indicates memory that is currently not used by anything.

What does the line “-/+ buffers/cache” indicate in the `free -m` output?

The line "-/+ buffers/cache" provides a more accurate representation of the memory usage on the system. It shows the amount of memory actually used by processes and the amount of memory free for use by applications.

What is swap memory and when is it used?

Swap memory is the space on the hard disk that is used when the physical memory (RAM) is full. If the system needs more memory resources and the RAM is full, inactive pages in memory are moved to the swap space.

Can the memory used for buffers and cache be freed up for use by applications?

Yes, the memory used for buffers and cache can be freed up by the system when necessary. It is not wasted memory and is being utilized to help the system run more efficiently, but if needed, it can be reclaimed and used by applications.

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