System.map ???

theonebeyond · 09-08-2004, 06:12 AM

Hi there!

I compiled one of my first kernels with openMosix patch relatively successfully ... nearly worked all right... just the sound isn't working ... but that's not so worse...

I added an entry for my new Kernel in /etc/lilo.conf ... now, I wonder what the System.map - file is all about and if I can add a line in lilo.conf to tell the System.map for a section without having to change the links in /boot

So, my questions are:
1) What is System.map? What does it do? Is it know to cause problems if used with other kernels?

2) Can I tell lilo to use a different System.map for every entry or do I have to change the link in /boot ?

Thanks a lot, Sascha

chakkerz · 09-08-2004, 06:59 AM

ok, last time i answered a question about this i got it wrong ... let me see if i can find the link ... here we go : http://www.linuxquestions.org/questi...669#post381669

I have as yet, never had an issue with System map, even when i go back to an older kernel. The bigger issue i've seen when doing this is that the modules are screwed up. But what i generally do is copy the new System.map file to the /boot directory and append the filename with the same string as the vmlinuz file/

As for the defining a separate System map via lilo ... no idea. (edit -> not necessary - check the last link).

for a bit of a gander ... do a
less /boot/System.map

(while root)
sorta interesting really, it looks like it starts with crc signatures, and moves on to addresses ...

For indepth stuff (including a detailed explanation of what System.map is) check out http://www.dirac.org/linux/systemmap.html/

Bruce Hill · 09-08-2004, 07:01 AM

For new kernels I name them and the new System map accordingly. Look at this ->

Code:

mingdao@paul:~$ ls -alc /boot/
total 4129
drwxr-xr-x   3 root root     432 2004-09-04 22:02 ./
drwxr-xr-x  22 root root    1784 2004-09-08 17:32 ../
lrwxrwxrwx   1 root root      37 2004-09-02 03:03 README.initrd -> /usr/doc/mkinitrd-1.0.1/README.initrd
lrwxrwxrwx   1 root root      21 2004-09-02 03:03 System.map -> System.map-ide-2.4.26
-rw-r--r--   1 root root  620999 2004-09-02 03:03 System.map-ide-2.4.26
-rw-r--r--   1 root root  662387 2004-09-04 22:01 System.map-new
-rw-r--r--   1 root root     512 2004-09-02 03:18 boot.0300
lrwxrwxrwx   1 root root      17 2004-09-02 03:03 config -> config-ide-2.4.26
-rw-r--r--   1 root root   41017 2004-09-02 03:03 config-ide-2.4.26
-rw-r--r--   1 root root    5032 2004-09-02 03:03 diag1.img
-rw-------   1 root root   46592 2004-09-04 22:02 map
lrwxrwxrwx   1 root root      18 2004-09-02 03:03 vmlinuz -> vmlinuz-ide-2.4.26
-rw-r--r--   1 root root 1248111 2004-09-02 03:03 vmlinuz-ide-2.4.26
-rw-r--r--   1 root root 1580910 2004-09-04 21:59 vmlinuz-new

amf57 · 09-08-2004, 06:19 PM

The idea behind the system map is that your root file system is usually located on a file system that is known about via a module. The real root file system can not be mounted if the kernel knows nothing about the file system. That is where a initial ramdisk is used. The system map is a map of consecutive blocks where the kernel is located. It is read by the bios which is allowed to execute code that is in the 1st 256 blocks of a hard drive. Thus your bios reads the block address (system map) which loads the kernel and that initial ram disk.
The initial ram disk typically has a command interpreter named nash, the commands insmod and modprobe, and the modules such as ext.o or scsi.o or lvm.o. The modules get loaded and now the kernel in memory knows about the file system on the hard drive and mounts the "real" root file system.