smem | Linuxaria

How to measure memory usage in Linux

Mar 032014

Article by me, first published on Openlogic.com

Whether you are a system administrator or a developer, sometimes you need to consider the use of memory in GNU/Linux processes and programs. Memory is a critical resource, and limited memory plus processes that use a lot of RAM can cause a situation where the kernel goes out of memory (OOM). In this state Linux activates an OOM killer kernel process that attempts to recover the system by terminating one or more low-priority processes. Which processes the system kills is unpredictable, so though the OOM killer may keep the server from going down, it can cause problems in the delivery of services that should stay running.

In this article we’ll look at three utilities that report information about the memory used on a GNU/Linux system. Each has strengths and weaknesses, with accuracy being their Achilles’ heel. I’ll use CentOS 6.4 as my demo system, but these programs are available on any Linux distribution.

Linux Terminal: Check who uses all your memory with smem

Guides, Pills 6 Responses »

Oct 202013

As system administrator, or simple user that uses Linux on its desktop sometime you notice that something it’s eating all the memory of your system.
As first thing be sure to understand how Linux manage memory, I’ve be called too many time by scared users that did a free and were unable to read its output properly, in short, don’t worry if the Linux Kernel it’s using your memory to cache file.

< rant on >

To my “beloved” users:

Be assured that the Kernel developers can do a better job than you (and me) in find a good algorithm to cache file and free that memory area when a process need it, so please don’t ask me to put in cron some job that run something like that :

echo 3 > /proc/sys/vm/drop_caches

After that you’ll have more free memory available on the system, true, but the system will have to re-read all the files from the disk, so in terms of performance this is usually a bad move.

< /rant >

But now let’s take a look at a nice small program that can help us in find which process/users are using, for real, the memory of our systems.