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Wizumwalt
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 Posted: Fri May 21, 2010 12:47 am Post subject: boot same kernel as is on host OS using KVM |
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I've got a few questions about how to use KVM. I've got my host OS talking to the guest OS, but I haven't gotten it to work the other way around yet. But the issue I'd like to figure out is how to load the same custom kernel I'm running on my host OS for the guest OS instead of the livecd which I load above, it's loaded w/ stuff I don't want, too big, and it's way to slow to load.
Here's my cmd to start kvm.
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kvm -net nic,macaddr=52:54:00:12:34:56 -net tap,ifname=qtap0,script=no,downscript=no -hda ./gentoo-i386.img -cdrom ./livecd-amd64-installer-2008.0.iso -boot d -m 512
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I've been using the gentoo kvm page on the wiki to get this far. Any help much appreciated. |
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Sadako
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| Posted: Fri May 21, 2010 2:13 am Post subject: |
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So, what have you been doing, booting the livecd via kvm and chroot'ing to gentoo-i386.img?
With qemu you have two options for booting kernels, one is to do everything within the vm as an a real host, ie compile the kernel within the vm, install it to /boot (within the vm) and install a bootloader to the mbr of your virtual disk (ie grub within the vm).
The other rather nice option specific to qemu is the '-kernel' option, where you specify a kernel image residing on the host system to boot, a bzImage which you'd typically copy to /boot.
The only problem with this is modules, if you're using a bzImage you've compiled on the host you'll need to copy the modules to /lib/modules within the guest, but other than that it's fantastic.
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Wizumwalt
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| Posted: Sat May 22, 2010 6:19 pm Post subject: |
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I got it to boot the image on my hard drive which is what I wanted, but I'd just like for someone to check over this line to make sure I'm doing this right. When I booted my guest OS, it was checking my hard disk and seemed to do a lot of disk access that I didn't think it should be doing. I thought this would run as an "read-only" to my hard drive. It's mounted all my partitions as rw and run the same init scripts as my host OS.
I'm just trying to get the exact same kernel as is running on my host OS to run on the guest OS so that I can do kernel mod development and not risk anything on my host OS. Am I running this in a parallel way that is dangerous to my host OS?
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kvm -net nic,macaddr=52:54:00:12:34:56 -net tap,ifname=qtap0,script=no,downscript=no -kernel /boot/kernel-2.6.32-gentoo-r7 -hda /dev/sda -boot c -m 512
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Sadako
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| Posted: Sun May 23, 2010 1:52 pm Post subject: |
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That looks very dangerous to me, it might be okay if one of the two mounts are read-only, but otherwise I'd say it's almost as dangerous as running fsck on a mounted filesystem...
You were running from a disk image earlier, why stop now?
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Wizumwalt
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| Posted: Sun May 23, 2010 5:29 pm Post subject: |
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| Hopeless wrote: |
You were running from a disk image earlier, why stop now? |
Because I don't know how to do it. If you know, please help w/ the command line so I can see what you mean. |
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Sadako
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| Posted: Sun May 23, 2010 6:09 pm Post subject: |
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Given what you've posted, this is all you should need; | Code: | | kvm -net nic,macaddr=52:54:00:12:34:56 -net tap,ifname=qtap0,script=no,downscript=no -kernel /boot/kernel-2.6.32-gentoo-r7 -hda ./gentoo-i386.img -boot c -m 512 |
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Wizumwalt
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| Posted: Wed May 26, 2010 12:32 am Post subject: |
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Yeah, I've tried that very same line. Didn't work. I get these results.
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VFS: Cannot open root device "<NULL>" or unknown-block(8,3)
Please append a correct "root=" boot option; here are the available partitions:
0800 10485760 sda driver:sd
0b00 1048575 sr0 driver:sr
kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(8,3)
Pid: 1, comm: swapper Not tainted 2.6.31-gentoo-r6 #2
Call Trace:
[<ffffffffff815e611>] panic+0xa0/0x14b
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Then tried this line thinking I need a root= line like the error says, and even give it the cd image ...
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kvm -net nic,macaddr=52:54:00:12:34:56 -net tap,ifname=qtap0,script=no,downscript=no -kernel /boot/kernel-2.6.31-gentoo-r6 -hda ./gentoo-i386.img root=/dev/sda -boot c -m 512 -cdrom ./livecd-amd64-installer-2008.0.iso
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And I get the same results as above. |
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Sadako
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| Posted: Wed May 26, 2010 4:12 pm Post subject: |
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Try this; | Code: | | kvm -net nic,macaddr=52:54:00:12:34:56 -net tap,ifname=qtap0,script=no,downscript=no -kernel /boot/kernel-2.6.31-gentoo-r6 -append root=/dev/sda -hda ./gentoo-i386.img -boot c -m 512 |
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Wizumwalt
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| Posted: Wed May 26, 2010 4:30 pm Post subject: |
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So I tried ...
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ic,macaddr=52:54:00:12:34:56 -net tap,ifname=qtap0,script=no,downscript=no -kernel /boot/kernel-2.6.32-gentoo-r7 -append "root=/dev/sda" -hda ./gentoo-i386.img -boot c -m 512
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And got some only slightly different results, instead of "Cannot open root device", I get "No filesystem could mount root".
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...
List of all partitions:
0800 10485760 sda driver: sd
0b00 1048575 sr0 driver: sr
No filesystem could mount root, tried: ext3 ext2 vfat mdsod iso9660
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(8,0)
Pid: 1, comm: swapper Not tainted 2.6.32-gentoo-r7 #2
Call Trace
[<ffffffff81545eba>] panic+0xa0/0x152
...
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Sadako
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| Posted: Wed May 26, 2010 5:03 pm Post subject: |
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What filesystem did you create on gentoo-i386.img when you formatted via the livecd?
I'm presuming you formatted the entire thing rather than partitioning?
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Wizumwalt
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| Posted: Wed May 26, 2010 5:53 pm Post subject: |
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I followed this howto ... http://en.gentoo-wiki.com/wiki/KVM
I'm a bit confused on your question. I used this command from the mentioned page to create a virtual disk image, gentoo-i386.img
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qemu-img create -f qcow2 gentoo-i386.img 10G
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But didn't format a livecd or see where in that page it mentioned to. I just downloaded the livecd image.
Could I be having problems because I'm trying to use a recent kernel (2.6.32) with an older livecd (livecd-amd64-installer-2008.0.iso).
I thought by giving the -kernel option, it would boot the kernel on the host os and override the kernel in the livecd. |
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bbgermany
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| Posted: Wed May 26, 2010 5:57 pm Post subject: |
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No, it would override the kernel on the system you want to boot inside your qcow image. You should mount the image and create a gentoo installation inside the image (basic stage3 should be fine). then boot with the following command. it should work then:
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kvm -net nic,macaddr=52:54:00:12:34:56 -net tap,ifname=qtap0,script=no,downscript=no -kernel /boot/kernel-2.6.31-gentoo-r6 -append root=/dev/sda -hda ./gentoo-i386.img -boot c -m 512
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it will boot the host kernel and changes into the system inside the ".img" file then.
bb
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Wizumwalt
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| Posted: Wed May 26, 2010 6:56 pm Post subject: |
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| bbgermany wrote: | | No, it would override the kernel on the system you want to boot inside your qcow image. |
yeah, sorry, I mispoke, that's what I meant.
And if I understood you correctly ... you mean just create a directory with a complete gentoo installation where I'd chroot into and finish off as a stage 3, just like in the docs? Then step out of that, mount it, and run kvm as you stated? Then where on that command line does it know where the mounted installation is? |
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bbgermany
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| Posted: Wed May 26, 2010 7:03 pm Post subject: |
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Yeah, kinda. You have created a qcow image. You need to run losetup and format it with a filesystem. Then you mount the image and extract a stage3 archive where you have mounted it. Then set a passwort for root, edit /etc/fstab for your root device (/dev/sda) and dont forget to set the right networkdevice. You will need a driver for this (virtio_net is doing fine for me, since i justed tested it right now). Then unmount the file and remove the loop device. Now you should be able to boot the system and start configuring your virtual gentoo.
if you need further help (especially the needed commands for this setup) just lemme know. Ill post it then.
bb
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Wizumwalt
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| Posted: Thu May 27, 2010 1:04 am Post subject: |
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| bbgermany wrote: |
if you need further help (especially the needed commands for this setup) just lemme know. Ill post it then.
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I'm definetly running into trouble with this. If you do happen to have those commands available, that would be a big help. |
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bbgermany
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| Posted: Thu May 27, 2010 12:06 pm Post subject: |
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Hi,
after you created your qcow image:
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losetup /dev/loop0 gentoo-i386.img
mkfs.ext3 /dev/loop0
mount /dev/loop0 /mnt
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now get the stage3 and maybe the portage-tree from the internet and continue with the installation doc at chapter 5: http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?part=1&chap=5 When you have finished installing up to the kernel, leave the chroot environment unmount the image and remove the loop device with the following commands and try starting with the kvm command from the previous posts:
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umount /dev/loop0
losetup -d /dev/loop0
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bb
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Wizumwalt
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| Posted: Fri May 28, 2010 1:18 am Post subject: |
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After mounting /dev/loop0 to /mnt/loop, I downloaded the stage3-amd64-xxx.tar.bz2 and tried to copy it to /mnt/loop, but I didn't have the space on /mnt/loop to hold it.
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$ sudo cp stage3-amd64-20100514.tar.bz2 /mnt/loop/
cp: writing `/mnt/loop/stage3-amd64-20100514.tar.bz2': No space left on device
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Should I have used something like the following w/ the size of both the portage tree and the stage3...bz2?
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$ losetup --sizelimit NNN /dev/loop0
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Or am I missing something?
Here's the results of when I made this fs and shows it's size.
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$ sudo mkfs.ext3 /dev/loop0
mke2fs 1.41.9 (22-Aug-2009)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
32 inodes, 256 blocks
12 blocks (4.69%) reserved for the super user
First data block=1
1 block group
8192 blocks per group, 8192 fragments per group
32 inodes per group
Writing inode tables: done
Filesystem too small for a journal
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 29 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.
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bbgermany
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| Posted: Sun May 30, 2010 4:55 pm Post subject: |
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Whats "df -h" showing for /mnt/loop?
May be your image is a bit small at all.
bb
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Wizumwalt
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| Posted: Thu Oct 07, 2010 9:39 pm Post subject: |
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Ok, so I've got my qcow2 image created ...
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qemu-img create -f qcow2 gentoo-i386.img 10G
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Then I ran losetup and formated it with a filesystem.
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$ losetup /dev/loop0 ./gentoo-i386.img
$ mkfs.ext3 /dev/loop0
$ losetup -a
/dev/loop0: [0811]:14655814 (/home/winky/kvm/gentoo-i386.img)
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This has caused some confusion for me. My understanding is that I can't use a qcow2 image like a normal raw image and mkfs on top of it because the qcow2 structure would be destroyed.
I was able to create a larger loop device by running it with the --sizelimit 10000000 param.
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$ mount /dev/loop0 /mnt/loop
$ mount
...
/dev/loop0 on /mnt/loop type ext2 (rw)
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I am now able to copy a stage3 file from the gentoo installation of chapt. 5 from the handbook. But I am still confused on what I just did by mkfs.ext3 over a qcow2 formatted loop device.
Can anyone help clarify this here? |
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