Matt-J.co.uk : Ramblings

Runs with xenblk loaded
Originally uploaded by TrX07

Following on from my last post, I finally got the centos 5.1 install running as a guest VM under solaris xVM.

The problem (as expected in the last post), was the initrd-xen ramdisk that was created when I installed the centos kernel-xen package did not have the xennet or xenblk kernel modules needed to run as a xen guest.

However, installing the kernel-xen package HAD installed the needed arch and version specific modules, just had not put them into the xen initrd (I think centos5.1 expects to be run as a dom0).

So, once chrooted into your centos5.1 filesystem, and after installing the kernel-xen package (yum install kernel-xen)

Unpack the initrd image:
gzip -cd < /boot/initrd-2.6.18-53.1.4.el5xen-img | cpio -iv
(would suggest running this in an empty folder, as it makes including the right files when rebuilding the initrd easier]

Next, find the modules needed in the centos filesystem:
find /lib/ | grep xenblk
/lib/modules/2.6.18-53.1.4.el5xen/kernel/drivers/xen/blkfront/xenblk.ko

find /lib/ | grep xennet
/lib/modules/2.6.18-53.1.4.el5xen/kernel/drivers/xen/netfront/xennet.ko

Then add these to the unpacked initrd (under lib dir):
cp /lib/modules/rest_of_path/xennet.ko \
/wherever/extracted/initrd/is/lib/.
cp /lib/modules/rest_of_path/xenblk.ko \
/wherever/extracted/initrd/is/lib/.

Finally, we need to tell the init script of the initrd to load the modules at boot, and re-pack the initrd.
(Im using vi as my editor, you could use nano, emacs etc)

vi /path_to_your_extracted_initrd/init

add 'insmod /lib/xenblk.ko'
and 'insmod /lib/xennet.ko'

before all the other ‘insmod’ lines, and save

Now re-pack your initrd:
cd /path_to_extracted_initrd
find . | cpio -c -o -v | gzip -9 -n > ../newinitrd-xen.img

This will have placed a file called newinitrd-xen.img, one folder back up your directory tree. Now make your xVM / Xen config file point to this .img file for the ‘ramdisk=’ option… and boot!

voila! away it goes!
(as you can see from the image, it does not crap out anymore at the ’switchroot’ stage, and you can see further up my xennet and xenblk modules being loaded)

Anyway, that’s all for now, hope someone finds this useful!
–Matt