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Kristi Jorgji
Asked: 2019-12-16 12:57:48 +0800 CST

How is possible that free memory goes down and used memory is not going up?

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I am collecting the results of free -m command on an ubuntu server every 5 seconds, and preparing a time series graph based on the values of free and used columns.

free -m
              total        used        free      shared  buff/cache   available
Mem:            992          43         709           5         238         791
Swap:           979

Sometimes the server that I am monitoring has a pattern like below: graph

I do not understand how the free memory can go down and used memory stay constant. Can it be some swap happening or something else ?

linux

1 Answers

  1. Free memory means unused memory. Since this is a waste of resources the Linux kernel uses it to cache/buffer files: access to memory is much faster than access to disks.

    In the output of free the total memory is divided into:

    • free memory,
    • used memory,
    • buff/cache.

    The available memory is what the system can use without killing applications or swapping.

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