Differences between revisions 14 and 15
Revision 14 as of 2006-03-21 23:58:33
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Comment: Both -net nic and -net user should be used...
Revision 15 as of 2006-06-23 19:35:25
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Editor: JoeyHess
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option, valid up to qemu-0.7.x option, valid up to qemu-0.7.x. qemu-0.8.1 does not need any net options,
it defaults to user-mode networking.


[http://fabrice.bellard.free.fr/qemu/ Official page]



#qemu IRC channel on irc.freenode.net


Qemu can be used to simulate various hardware configurations and to easily test the debian installer in various conditions; it's great for testing "delicate" things like a partitioner, since disk devices are usually represented by files.

It can be used also to emulate other architectures: I tested amd64 and powerpc versions on the installer on my i386 host machine. At the moment (qemu-0.8.0) sparc and ARM are being worked on and have some basic support.

Here some possible d-i boot configurations:

  • floppy installs
  • install over serial console
  • installs from USB (??)
  • lowmem installs

Basic setup

First of all, you need to create a file which will acts as an hard disk for the virtual machine:

$ qemu-img create hd_img.img 500M

You can then download an iso image of the installer, or create one yourself; you can then run a g-i session by running the following command:

$ qemu -net nic -net user -cdrom mini.iso -hda hd_img.img -boot d

note that "-net user" has to be used with qemu-0.8.0 in place of the "-user-net" option, valid up to qemu-0.7.x. qemu-0.8.1 does not need any net options, it defaults to user-mode networking.

Qemu monitor

Qemu has a "monitor" (ctrl-alt-2) which can be used to access various funcionalities such as:

  • "screendump" which can be used to take a screenshot of the VM screen
  • "sendkey" is very useful when you want to switch to VT2 during a g-i vession ("sendkey ctrl-alt-f2)
  • "gdbserver" is useful for attaching gdb to a process running inside the VM
  • "loadmem/savemem" used to save/restore the state of the VM, saves you a lot of time when you have performed all the steps needed to reproduce a bug

Communicating with the VM

You often need to copy file from the VM to the host (i.e. log files), or you need to copy files from the host to the VM (i.e. some udebs).

There are various ways of achieving this; if you have an ssh client inside the VM, for example, you can scp files from/to the host. When you boot a (standard) g-i image, it takes a few steps before you can have the ssh client into the VM, so you might find useful doing the following:

wget can be used to copy files from your host (or somewhere on the net); note that the wget command is always included in the mini.iso

netcat can be use to export files from the VM to the host: you first need open a listening connection on the host

  $ nc -l -p 1111 > vm.log

then, you can run the following command to export a file from the VM:

  # cat logfile.txt | nc IPADDR_HOST 1111

you should find the file vm.log on you host, with the content of logfile.txt Obviously networking inside the VM has to up before being able to do this.

Floppy install

To test an installation from the floppy images, you first need to grab [http://people.debian.org/~joeyh/d-i/images/daily/floppy/boot.img boot.img] and [http://people.debian.org/~joeyh/d-i/images/daily/floppy/root.img root.img] and use the files as if they were floppy disks:

$ qemu -user-net -fda boot.img -hda hd_image.img -boot a

once you're asked to insert the root disk, just switch to "monitor" (ctrl-alt-2) and

(qemu) change fda root.img

switch back to d-i (ctrl-alt-1) and press ENTER

install over serial console

you can easily test an installation over a serial console by passing the following string at the boot prompt:

install console=ttyS0,9600,n8

you can then reach the serial console by pressing ctrl-alt-3