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# <a name="Hurd_on_QEMU"> </a> Hurd on QEMU
... by the way, there is available an already prepared [disk image with an installation of the Debian distribution of GNU/Hurd](http://www.numenor.art.pl/balrog/hurd/) for QEMU.
## <a name="What_is_Needed"> What is Needed </a>
1. First thing is to install [[QEMU]].
2. [Debian grub boot disk package](ftp://ftp.debian.org/debian/pool/main/g/grub/) for the floppy disk image needed for booting. You should get the [0\.95 version](ftp://ftp.debian.org/debian/pool/main/g/grub/grub-disk_0.95+cvs20040624-17_all.deb) as anything later doesn't seem to work properly. The floppy boot image is called `grub-*-i386-pc.ext2fs.gz` and you will need to decompress this. I have renamed mine to `floppy.img`.
3. You will need a [Debian/Hurd installation CD](http://www.debian.org/ports/hurd/hurd-cd). I suggest using K9 as K10 seems to have some issues.
## <a name="Installing_Debian_Hurd_with_QEMU"> </a> Installing Debian/Hurd with QEMU
First off you will need to create a disk image using `qemu-img`. I have set mine to 2 gigabytes, although you should be able to get away with less.
$ qemu-img create hd0.img 2G
Next you will want to start up QEMU and begin the installation process. The first time you run it you will want to use the `-boot d` option to boot off the cdrom.
$ qemu -hda hd0.img -cdrom debian-K9-hurd-i386-CD1.iso -fda floppy.img -boot d
Now at his point do the regular install using `hd0` as your harddrive. Partition it and install the base system. Once you have finished installing the base system select the reboot option as this will ensure the disk is properly un-mounted. When the Debian CD menu comes up again simply close QEMU.
Now run your image with floppy booting and finish the install (`./native-install` .. etc).
**Important:** Notice the `-M isapc` option. This is needed for the version of gnumach that comes with K9 (or K10). Once you get your system running you can update to the latest version of gnumach which does not have this restriction.
**Important:** If you are running an older version of QEMU (less than 0.8) then you will need to use the `-isa` option instead of `-M isapc`.
$ qemu -hda hd0.img -cdrom debian-K9-hurd-i386-CD1.iso -fda floppy.img -boot a -M isapc
## <a name="Mounting_Disk_Image_on_Host"> Mounting Disk Image on Host </a>
You may wish to mount your disk image on your host system to transfer files. To do this you will first need to find the offset of the partition you wish to mount.
# fdisk -ul hd0.img
...
128 heads, 63 sectors/track, 0 cylinders, total 0 sectors
Units = sectors of 1 * 512 = 512 bytes
Device Boot Start End Blocks Id System
hd0.img1 * 63 3515903 1757920+ 83 Linux
hd0.img2 3515904 4193279 338688 82 Linux swap / Solaris
Now take the number of sectors for the beginning of the partition and multiply it by the sector size. My partition starts at sector 63 and I have a sector size of 512 therefor my offset is 32256.
# mount -o loop,offset=32256 hd0.img /mnt/diskimage
## <a name="Networking_in_QEMU"> </a> Networking in QEMU
If you just want to access the internet from within QEMU, you can setup pfinet for QEMU's user-networking:
# settrans -afgp /servers/socket/2 /hurd/pfinet -i eth0 -a 10.0.2.15 -g 10.0.2.2 -m 255.255.255.0
(See also <http://fabrice.bellard.free.fr/qemu/qemu-doc.html#SEC30>.)
Outgoing internet connections should just work then, although you might have to setup nameservers in `/etc/resolv.conf` as well.
If you want to connect from the host system to the Hurd system running in QEMU, you need to setup something more advanced, like bridged networking.
## <a name="Bridged_Networking"> Bridged Networking </a>
### <a name="What_is_Needed"> What is Needed </a>
1. Your Linux kernel will need 802.1d Ethernet Bridging support and TUN/TAP device driver support.
2. You will need to install [bridge-utils](http://bridge.sourceforge.net).
### <a name="Setting_Up_the_Host_Bridge"> Setting Up the Host Bridge </a>
You need to setup a bridge on the host first. This assumes `eth0` is down. I have modified my hosts network startup scripts to automatically setup a bridge, you may want to do this also.
# brctl addbr br0
# ifconfig eth0 0.0.0.0 promisc up
# brctl addif br0 eth0
At this point you will need to setup `br0` as you would normally `eth0` (`dhcpcd br0` for example).
### <a name="The_qemu_ifup_Script"> The qemu-ifup Script </a>
This script gets called when QEMU starts and will attach the tun device to the bridge. QEMU will look for this file at `/etc/qemu-ifup` and that is where I keep mine.
#!/bin/sh
sudo ifconfig $1 0.0.0.0 promisc up
sudo brctl addif br0 $1
### <a name="Setting_up_the_Network_in_the_Hu"> Setting up the Network in the Hurd </a>
Now it is time to start-up your QEMU Hurd system and get networking going in there.
**Important:** Remember you may need to use the `-M isapc` or `-isa` flag if using an older version of the gnumach package.
$ qemu -hda hd0.img -cdrom debian-K9-hurd-i386-CD1.iso -fda floppy.img -boot a -net nic -net tap
Once you have logged in as `root` run the `pfinet` translator with values that apply to your network. Think of your QEMU client as another computer in your network.
# settrans -fgap /servers/socket/2 /hurd/pfinet -i eth0 -a xxx.xxx.xxx.xxx -g xxx.xxx.xxx.xxx -m xxx.xxx.xxx.xxx
That should do it! Do not forget to edit/update `/etc/resolv.conf` to get DNS working.
## <a name="Related_Links"> Related Links </a>
These are links that users of [[HurdOnQEMU]] may find helpful.
[[DebianAfterInstall]] - good source of information pertaining to your system after installation.
[[Hurd/QemuImageForL4]] - a QEMU image for the Hurd/L4 project.
## <a name="TODO"> </a> TODO
[[Hurd/HurdIRC]], 2007-07-04.
<azeem-uni> so, is there a way to use a Debian GNU/Hurd partition (/dev/hda6) with qemu directly?
<tschwinge> Don't dare to do that, please.
<tschwinge> It will lead to inconsistencies.
<tschwinge> Because the Linux kernel thinks that it has complete control over the disk, or something.
<tschwinge> In theory you could run something like ``-hda /dev/hda'', having GRUB installed on there to offer you to boot your Hurd system from hda6 and that will even work, but then don't get the idea to stop qemu, mount that partition on your Linux system and restart qemu. That's where I got lots of inconsistencies then, afterwards.
<azeem-uni> it's probably the same problem as having that partition mounted, suspending to disk, booting into it in the Hurd, and resume Linux
<neal> right
<tschwinge> That's a different problem.
<tschwinge> Then the partitoon is still mounted.
<neal> no, I think it is basically the same problem
<tschwinge> The file system stuff is cached in the kernel.
<neal> you have data that has not been written to disk yet
<tschwinge> Right.
<neal> and neither is prepared for the resource to be shared
<tschwinge> In the azeem-uni scenarion the data is on the file system layer and in my scenarion it's some disk block caching inside the Linux kernel, I guess.
<azeem-uni> anyway, do you guys think if I use -hda /dev/hda and tell Grub to boot off /dev/hda6, that the rest of hda should be fine, right?
<azeem-uni> maybe adding -snapshot makes it totally safe
<neal> azeem: Should be fine.
<tschwinge> Yes.
The problem is actually that the linux block cache doesn't make any consistency between /dev/hda and /dev/hda6, so if you give /dev/hda to qemu, qemu writings won't be consistent with mounting /dev/hda6 in linux. You can give /dev/hda6 directly to qemu and it will be fine.
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