[fedora-virt] How can we pass kernel arguments(e.g:ks=hd:/dev/..) to a cdrom-based guest install?

[Dor Laor]

On 02/08/2010 01:03 PM, Dor Laor wrote:
> On 02/04/2010 03:51 PM, James Laska wrote:
>> On Thu, 2010-02-04 at 10:38 +0000, Daniel P. Berrange wrote:
>>> On Thu, Feb 04, 2010 at 10:45:37AM +0800, Li Ming wrote:
>>>> Hi,
>>>>       How can I pass the ks argument to a guest during install? I am
>>>> writing an auto install python script,I can use virt-install --location
>>>> install_tree --extra-args ks=...., but this will active the network, we
>>>> want to mirror a true DVD install. If use virt-install --cdrom will
>>>> solve this issue, we have a bad way to pass ks argument,uncompress the
>>>> ISO,update the syslinux kernel args,then build the ISO again,but this
>>>> will consume big resource,not a good way. Does someone have good
>>>> suggestion for me to pass ks arg to kernel while using virt-install
>>>> --cdrom in python script?
>>>
>>> It is only posible to pass kernel boot args when booting off kernel/initrd
>>> direction (ie --location).  With --cdrom the BIOS is in charge. So if you
>>> need to pass args, then you'll have to modify your ISO image to include
>>> them directly.
>>
>> We can certainly try modifying the ISO image itself, but we'd prefer
>> leaving the ISO image pristine if possible.
>>
>> Does the KVM autotest suite have any workarounds or example methods for
>> modifying the boot args when booting an ISO image?  Perhaps running
>
> KVM autotest uses qemu directly and there is no issue there, -cdrom do
> tell the bios where to boot from but -kernel still has the right effect.

Here is Lucas's answer (CCed) about how it works with kvm autotest, note 
that it's different and the ks parameters go through pxe config:

"
Here is how autotest works to perform CD based unattended installs:

  Linux guests/kickstart:
   * qemu boots over the network in usermode, using the pxelinux boot
loader, which is served on qemu builtin tftp server.

There is a preparation script, called unattended.py, that picks vmlinux
and initrd.img from the CD and puts them under the tftp server
directory, also writing a pxe boot entry config

         pxe_config = open(pxe_config_path, 'w')
         pxe_config.write('DEFAULT pxeboot\n')
         pxe_config.write('TIMEOUT 20\n')
         pxe_config.write('PROMPT 0\n')
         pxe_config.write('LABEL pxeboot\n')
         pxe_config.write('     KERNEL vmlinuz\n')
         pxe_config.write('     KERNEL vmlinuz\n')
         pxe_config.write('     APPEND initrd=initrd.img %s\n' %
                          self.kernel_args)

The pxelinux boot entry informs kernel params, in those params we inform
that a kickstart is going to be used, and that kickstart resides on the
floppy:

02/07 22:49:50 DEBUG| utils:0105| [stdout] kernel_args: ks=floppy 
nicdelay=60

Command line looks like:

/usr/local/autotest/tests/kvm/qemu -name 'vm1' -monitor 
unix:/tmp/monitor-20100207-221920-Q1pS,server,nowait -drive 
file=/tmp/kvm_autotest_root/images/rhel5-64.qcow2,if=ide -net 
nic,vlan=0,model=rtl8139,macaddr=52:54:00:12:36:40 -net user,vlan=0 -m 
1024 -smp 2 -drive 
file=/tmp/kvm_autotest_root/isos/linux/RHEL-5.4-x86_64-DVD.iso,index=2,media=cdrom 
-fda /usr/local/autotest/tests/kvm/images/floppy.img -tftp 
/usr/local/autotest/tests/kvm/images/tftpboot -boot d -bootp /pxelinux.0 
-boot n -redir tcp:5000::22 -vnc :0

The kickstart in its turn specifies the cdrom as the source for the
installation.

So yes, in this case, both floppy and cdrom parameters are just
providing a IDE cdrom and a floppy, the vm is not booting from there,
but rather from the network.

Windows guests/answer files:
  * qemu boots over the cd, and windows cds will look for floppies during
the boot process, if they find floppies then they will look for an
answer file, if they find it, they proceed with automated installation.

Bottom line, we used a slightly convoluted system to specify a kickstart
in the floppy, mostly because I wanted to keep the same mechanism
(unattended file in the floppy for both windows and linux).

So this could be a suggestion for the guy wanting to specify the kernel
arguments.

Let me know if that explanation was good enough and if you want me to
lend a hand on this,

Lucas
"
>
>> virt-viewer and _somehow_ issuing keyboard events to adjust the boot
>> args appropriately?  Or, can an ISO be mounted as a disk in the guest
>> and modified somehow using libguestfs?
>>
>> Thanks,
>> James
>>
>>
>>
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