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[Qemu-devel] Re: No useful documentation.

From: Emmanuel Charpentier
Subject: [Qemu-devel] Re: No useful documentation.
Date: Sun, 09 Jul 2006 09:26:41 -0000
User-agent: Thunderbird (X11/20060615)

Dear Daniel,

Daniel Carrera a écrit :

I write here because there doesn't seem to be a Bugzilla for qemu and
whoever is responsible for the qemu documentation must be here.

The documentation is quite worthless.

I cannot agree. Qemu doc is (more or less) adequate *for people already familiar with coping with bare hardware*. Read along

I'm sure you don't like hearing that, but consider that it doesn't
actually show the user how get qemu to do what qemu is supposed to di
(ie. run a host OS). Ok, it tells me how to create a blank disk image,
that's great, but how do I create a disk image with something bootable
on it? Sorry, no information on that. I expect that the most typical use
case for qemu is running Windows under Linux, so you'd expect to see
some documentation for that, right? Nope, none. Sure, there are
trouble-shooting tips, but what use are trouble-shooting tips if you
can't even get started?

The information you're lacking seems not to be how to use QEMU, but rather how to install an OS on a bare ("virgin") system. This is not QUEM related. This was universal knowledge back in early PCs day (PC-XT, to be precise) ; the quasi-universal dissemination of preinstalled OSes (thanks to Microsoft's and Apple's grip on the market), made this knowledge unuseful for most of users, therefore more and more a nerd's knowledge.

In short : in order to install an OS on bare hardware, you have to boot this hardware on something coming in removable media, then use this installer to install the OS.

In olden days of yore, you booted on diskettes (or even on a tape (yuck !)), ad used the resulting running mini-OS to read another support (diskettes or tape(s) again) to install its content on the hardware hard disk. Nowadays, the boot medium and the OS distribution medium are merged in a common CDROM. So you boot an installer from the (first) installation CDROM and use this installer to install the OS on the disk. Since booting and installing come from the same medium, the distinction became more and more blurred, thanks to the willingness of distribution creators more and more willing to "help" "unskilled" end-users. Hence the confusion...

With QEMU, the process is the same in principle, but slightly different in realization, due to the difference between real and simulated hardware.

You have to have an installation medium for your target OS, either physical (e. g. a cd-rom) or virttual (e. g. a cd-rom ISO image).
You start  by creating a *virgin* hard disk image (with qcow).
You then boot qemy by pointing it to your newly-created hard disk image as your first hard disk (e. g. -hda myharddisk.qcow), to your distribution medium or medium image as a cdrom (e. g. -cdrom /dev/cdrom, or -cdrom mymediumimage.iso), and telling qemu to boot on the distribution medium (image) with -boot d.

The installer boots on the emulated system and hand-helds you to install the target OS on what it thinks is the primary hard disk. At the end of installation, you will be prompted to reboot your system on yournewly-installed OS. At this stage, you should terminate QEMU and restarting it with the sames options as before, *except for the -boot option,*, which you change to "-boot c". This directs QEMU to boot on your newly-loaded hard disk.

I've looked at qemu several times over the past several years. Every
time I get excited at the prospect of migrating people to GNU/Linux by
letting them run the one windows app they need...

For many cases (but not all, by a long way !), wine is a better solution to run a couple of "irreplacable" (??) Windows apps. Installing a full virtual machine and OS to run one app is a bit like using a sledgehammar to swat a fly...

                                                   and every time I hit a
brick wall, as qemu fails to actually do anything useful.

Try to take this approach: You are writing to a technically competent
user (perhaps a sysadmin) who wants to run Windows under Linux with qemu
(perhaps to migrate some of the company computers). He has a Windows
install CD, he has qemu installed, and is ready to go. Please write
something that this person can use to get Windows running under qemu.

I have to point out that any sysadmin worth his salt would have serious knowledge of system installation procedures, much more than what I've sketched above. This is ultrabasic knowledge to a sysadmin...

                                        Emmanuel Charpentier
                                Remembering way more CP/M, TRSDOS
                                VMS, MS-DOS, Unix, Windows and Linux
                                installations than he wishes to
                                acknowledge... Shit, I even remember
                                how to boot a Mini-6 (a nice Bull mini
                                from the 70's) !

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