Monday, April 20, 2009

Increase Swap Memory in Linux


Linux Free Command
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The Linux Free Command
Getting started

The linux free command allows us to check free/used memory on the system The output below is the result of running free -m on my system (-m means output is in MB):

total used free shared buffers cached
Mem: 3856 1121 2735 0 17 180
-/+ buffers/cache: 923 2933
Swap: 2533 1044 1489

Output explained

The first line starting with Mem: gives us the following information:

* total - is the total avaialble RAM (== Physical Memory) after subtracting the amount used by the kernel! In my case I have 4GB RAM and the total displays less than this.
* used - is the part of the RAM that currently has information in it that can be of use to the system (remember: unused RAM is useless, try to maximise this value)
* free - is just total-used
* shared - is the amount of memory shared between processes
* buffers and cached - the cached data and buffers for IO

The second line starting with -/+ buffers/cache: tells us how much of the memory in the buffers/cache is used by the applications and how much is free. Keep in mind that in general the cache is filled with disk IO cached data. The cache can be very easily reclaimed by the OS for applications. Let BUFFERS + CACHED from first line be value X.

X subtracted from the USED memory from the first line gives how much RAM is used by applications (USED value on second line)

X added to the FREE memory on the first line gives how much RAM applications can still request from the OS.

While the first line handles the values of currently used RAM, including applications and caches (but excluding kernel), the second line gives info on application related memory: how much is currently in use and how much is there still available for the applications.