Re: How to boot ISO using grub on SLES 11 SP4

[Glenn Washburn]

On Mon, 31 Aug 2020 19:14:53 +0530
Sac Isilia <udaypratap.singh65@gmail.com> wrote:

> Hi Team,
> 
> I am currently facing an issue that currently SUSE itself is not
> providing the support. Below is the case scenario description
> 
> We have one SLES 11 SP4 machine in our environment that is hosted on
> Azure. We need to upgrade the machine to SLES 12 SP5 latest service
> pack since SLES 11 SP4 is now EOL. Earlier we used to simply attach
> the ISO to VmWare vsphere and do the upgrade , but since now our
> machine sits in azure and there is no way to attach the ISO to do the
> upgrade.
> 
> I thought of another way of doing it but I dont know the technical
> details to do it. I am thinking of copying the ISO to our server and
> mount it. The server is using grub as the boot loader. Now i dont
> know what changes I need to make in grub on SLES 11 SP4 so that if I
> restart I get the SLES 12 SP5 ISO boot prompt from where I can
> proceed with my upgrade.

Another option is to skip Grub altogether by using kexec, assuming your
current install supports kexec.  Also, the iso will need to support
loopback mounting (I think all major distros do).

So this would look something like:
1. Understand what kernel parameters grub uses to boot into upgrade iso
2. Loopback mount iso
3. kexec -l <iso kernel> --append="<kernel parameters>
iso-scan/filename=<path to iso from root of device>" --initrd="<iso
initrd>"
4. profit!

This has the added benefit that by cutting out grub, you eliminate a
potential point of failure (eg. grub may not support reading the device
the ISO is on).

Glenn