compiling the 3.2 kernel

[mimosa]

I recently installed the current kernel (just for the hell of it really) and now I'm recompiling it. I have a practical and a theoretical question.

The practical question is that according to the Slackbook, I should back up the old files then copy the new kernel to /boot/vmlinuz, and the new system map to /boot/System.map. Those are symlinks so I presume the effect will be to overwrite the two corresponding files in /boot that I backed up. But what about /boot/config, another symlink to a file in /boot?

Then I just need to run lilo and reboot, I take it; and if it doesn't work I just put the backed up files back and run lilo again.

The theoretical question is if I'm just doing this for fun (I did select one or two config options to do with virtualisation, but I don't really understand what they will do), is it worth the bother? Will compiling the kernel locally attune it to my unglamorous Intel Atom CPU and make everything run faster?

[Shador]

The practical question is that according to the Slackbook, I should back up the old files then copy the new kernel to /boot/vmlinuz, and the new system map to /boot/System.map. Those are symlinks so I presume the effect will be to overwrite the two corresponding files in /boot that I backed up. But what about /boot/config, another symlink to a file in /boot?

From my /boot:

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lrwxrwxrwx 1 root root      37 Mai 27  2011 README.initrd -> /usr/doc/mkinitrd-1.4.6/README.initrd
lrwxrwxrwx 1 root root      24 Jun 17  2011 System.map -> System.map-huge-2.6.37.6
-rw-r--r-- 1 root root 3015272 Aug  4  2011 System.map-2.6.39.3-ice
-rw-r--r-- 1 root root 2706772 Apr 10  2011 System.map-huge-2.6.37.6
-rw-r--r-- 1 root root     512 Jul 14  2011 boot.0820
-rw-r--r-- 1 root root     312 Jan 22 18:35 boot_message.txt
lrwxrwxrwx 1 root root      20 Jun 17  2011 config -> config-huge-2.6.37.6
-rw-r--r-- 1 root root  117248 Aug  4  2011 config-2.6.39.3-ice
-rw-r--r-- 1 root root  112298 Apr 10  2011 config-huge-2.6.37.6
drwxr-xr-x 5 root root   12288 Feb 28 21:29 grub
-rw-r--r-- 1 root root  308278 Mär 27  2011 salix.bmp
lrwxrwxrwx 1 root root      21 Jun 17  2011 vmlinuz -> vmlinuz-huge-2.6.37.6
-rw-r--r-- 1 root root 5599280 Aug  4  2011 vmlinuz-2.6.39.3-ice
-rw-r--r-- 1 root root 5866144 Apr 10  2011 vmlinuz-huge-2.6.37.6

Then I just need to run lilo and reboot, I take it; and if it doesn't work I just put the backed up files back and run lilo again.

I recommend adding an entry for each kernel in your bootloader. That way you don't even need a rescue system or anything to recover. Actually with grub2 you can generate a configfile containing an entry for each kernel automatically. Usefull if switching, building and changing kernels a lot.

I did select one or two config options to do with virtualisation, but I don't really understand what they will do

Bad. In this case it shouldn't matter, but the kernel could become unbootable. No more, no less.
Regarding Virtualisation. There are two kinds of options. Those affecting virtualisation capabilities/performance when the kernel is used as host and those when the kernel is running as guest.
I think for all of the first modules are built by default. The latter is disabled, I think, - probably due to overhead - and offers only performance benefit when used as a guest.

Will compiling the kernel locally attune it to my unglamorous Intel Atom CPU and make everything run faster?

No, definitely not noticeably. Maybe some irrelevant µs. Only some options and patches like (BFS, BFQ, ...), may offer some noticable performance benefits. (Unless in very special use cases of course. When deploying embedded or other fixed hardware systems you might choose such tweaks too.)

I usually build kernels like this:

1. Obtain the kernel-sources, e.g. by copying /usr/src/linux-<ver> to your home
2. Patch and configure them as desired (Don't forget to add a local version)
3. Build the kernel
4. Put the files into /boot (I wrote a script for that purpose)
5. Install kernel modules: make modules_install
6. Update your bootloader, with grub2 it's as simple as update-grub or grub-mkconfig

The aforementioned script (to be called from the top directory of the kernel source):

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#!/bin/bash

if [ "$(whoami)" != "root" ]; then
  echo "Need root!"
  exit
fi

linvercode="$(grep 'LINUX_VERSION_CODE' include/linux/version.h | sed -e 's/.* \([0-9]\+\)/\1/')"
a="$(($linvercode >> 16))"
b="$(($linvercode >> 8 & 255))"
c="$(($linvercode & 255))"
probedver="$a.$b.$c.$(cat .version)"
probedlocalver="$(grep "CONFIG_LOCALVERSION=" .config | sed -e 's/[^"]*"\([^"]*\)"/\1/')"
kernelver=${1:-${probedver}}${probedlocalver}
if [ "$DRY" == "true" ]; then
   dry='echo'
fi

$dry cp -v arch/x86/boot/bzImage /boot/vmlinuz-$kernelver
$dry cp -v .config /boot/config-$kernelver
$dry cp -v System.map /boot/System.map-$kernelver

[mimosa]

Thanks Shador, that's very helpful. Incidentally, the Slackbook says to copy the new kernel to /vmlinuz, I assume that should be /boot/vmlinuz? That's what I did, anyway. The Slackbook doesn't mention any of those other files, either.

I went ahead and the kernel didn't boot, so I restored the backed up files and ran lilo again. All well!

[thenktor]

I usually build kernels like this:

1. Obtain the kernel-sources, e.g. by copying /usr/src/linux-<ver> to your home
2. Patch and configure them as desired (Don't forget to add a local version)
3. Build the kernel
4. Put the files into /boot (I wrote a script for that purpose)
5. Update your bootloader, with grub2 it's as simple as update-grub or grub-mkconfig

I'm doing the same, except for (5). I just add the new kernel to my lilo.conf

BTW: thanks for the script. It's a bit boring to copy the files by hand and add the kernel version to each file

[thenktor]

Shador, your script works fine, but I've forgotten to install the modules

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uname -a
Linux pinkfloyd 3.2.12-bfs-slayer #2 SMP Fri Mar 23 11:23:17 CET 2012 x86_64 AMD Athlon(tm) II X4 610e Processor AuthenticAMD GNU/Linux

[Shador]

Shador, your script works fine, but I've forgotten to install the modules

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uname -a
Linux pinkfloyd 3.2.12-bfs-slayer #2 SMP Fri Mar 23 11:23:17 CET 2012 x86_64 AMD Athlon(tm) II X4 610e Processor AuthenticAMD GNU/Linux

You're right. Wrote those steps by memory. Now corrected.

[thenktor]

Actually it was my fault, but I guess a script that installs the kernel could also install the modules And I've found a small issue: there is something wrong with the version renaming. My kernel files are named 3.2.12.2 instead of 3.2.12 in the boot folder.

[Shador]

It could, but I didn't want it to. After all it's just one simple command and just because it was more than that for the kernel installation, I wrote that script.

[thenktor]

Yes, it doesn't really matter