Friday, January 15, 2010

dmesg Command in Linux

This article serves as an introduction , to one of the rarely known UNIX commands to general under-graduate students , the "dmesg" command .

Definition :
dmesg - print or control the kernel ring buffer  .

What do we mean by the term Kernel Ring Buffer ?

In simplest terms it is a log which contains messages from the kernel .

For example we can try a simple command :

[root@localhost]#dmesg | grep Memory 
[    0.000000] Memory: 371348k/393152k available (4565k kernel code, 21120k reserved, 2143k data, 540k init, 0k highmem) 

This command gives certain information about the memory reserved by the kernel at boot time .

Uses of dmesg command:

1) Useful to extract information , about the functioning of various kernel modules basically the device drivers.

Therefore , this message was  logged in by the kernel at the time of file system mounting and can be extracted using the dmesg utility .

Useful Links :
1 ) 
Offers a simple and an effective example .

2) For more advanced usage of dmesg command refer :
 The link mentioned , also provides the answer to the general query of what is a Ring Buffer.

 For those interested to see the file from which we can see the input file to the dmesg command ,
open the file /var/log/dmesg with any standard text editor.

Hope this solves some of your queries.

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