System.map purpose?

Richard Lightman richard at nezumi.plus.com
Fri Nov 1 17:34:38 PST 2002


* David C <david at desolateonline.com> [2002-11-02 01:20]:
> 
> What is the System.map file in the /boot directory for? The reason I ask 
> is because I have been using my hosts' LILO so far, simply because I 
> like the nice graphical menu RH uses for it. Now I'm going to use the 
> 'LILO Beautified' hint to attempt to mimic this and hopefully improve 
> upon it within LFS. This will mean switching over to booting from LFS's 
> LILO and /boot directory, which has it's own System.map file.
> 
> In the past, I'm pretty sure I've used LFS' System.map for both LFS and 
> RH with no ill effects apparent, but I am wondering if they truly are 
> interchangeable, and just what exactly they are for anyway.
> 
> I know they are not identical because the file size is different by a 
> sizeable amount.
> 
> I assume they must be at least somewhat interchangeable, since when 
> booting multiple kernels I've never seen mention of requiring multiple 
> System.maps...
> 
The System.map is used to convert addresses (meaningless numbers) into
symbol names. This is only important when something has gone badly
wrong in the kernel, and you want to find out what.

You can find all the gory details in man klogd.

The important bit is that klogd will look for the system map in these
places, unless you tell it otherwise:

/boot/System.map
/System.map
/usr/src/linux/System.map

These are all really stupid places to put the system map. If you have
more than one kernel, the file will only be correct for one.

A more sensible place to put the map is:
/lib/modules/$(uname -r)/System.map

You can tell klogd to use the correct map by adding:
 -k /lib/modules/$(uname -r)/System.map

to its command line in the init scripts. Modutils already knows about
this file, and will not mistake it for a module.


Richard



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