Re: EFI PXE boot using grubx64.efi - Large images

[Randy Goldenberg]

Disclaimer: For PXE booting I use iPXE, not grub. I successfully EFI booted the 
CentOS 7.4 LiveCD using the procedure outlined below, and iPXE.  I would not 
expect PXE booting with grub to be substantially different.

I found a CentOS 7 LiveCD that appears to be the one you're trying to boot, on 
a CentOS mirror at 
centos/7.4.1708/isos/x86_64/CentOS-7-x86_64-LiveGNOME-1708.iso.  This is the 
image used.  For preparing your PXE booting setup, mount the ISO.

The initrd inside the ISO at isolinux/ does not support booting over the 
network.  Various attempts to inject the needed drivers using dracut were 
unsuccessful.  Instead of the kernel and initrd in the ISO, I used the kernel 
and initrd available on CentOS mirrors at 
centos/7.4.1708/os/x86_64/images/pxeboot.  Put these files wherever you put 
stuff to be loaded by grub; probably your tftp directory (iPXE can access these 
using http, much faster).

The ISO contains a squashfs archive of the root file system used for live 
booting, in the "LiveOS" directory.  Copy the LiveOS directory to your http 
server.

The ISO has a boot menu at isolinux/isolinux.cfg.  This was the model for the 
iPXE boot entry below, tweaked a bit for loading the root file system over 
http.  It has also been tweaked for EFI booting, by adding the name of the 
kernel and a definition of an initrd variable to the boot environment.  For 
details on the boot options, consult the dracut manual.  I would expect 
adjusting it to fit the conventions of grub PXE booting to be trivial:

kernel ${boot-url}CentOS-7-x86_64-LiveGNOME-1708/vmlinuz
initrd ${boot-url}CentOS-7-x86_64-LiveGNOME-1708/initrd.img
imgargs vmlinuz initrd=initrd.img ip=dhcp 
root=live:${boot-url}CentOS-7-x86_64-LiveGNOME-1708/squashfs.img 
rootfstype=auto ro rd.live.image quiet  rhgb rd.luks=0 rd.md=0 rd.dm=0

"${boot-url}" is defined elsewhere.  Replace it with the URL for the files on 
your http or tftp server, as appropriate.

Please let me know if you have any questions.

Thanks,

Randy

On Thursday December 28, 2017, Locane wrote: 

> I know that the files exist and are accessible, since they are the same files
> that regular legacy PXE references.  That root= parameter is in the legacy PXE
> menu entry too.
>
> Here's the legacy PXE menu entry that works if you're curious:
>
> LABEL LiveCD
>         kernel /images/LiveCD/vmlinuz
>         MENU LABEL ^LiveCD
>         append initrd=/images/LiveCD/initrd.img ksdevice=bootif root=live:/
> boot.iso kssendmac text  ks=http://<SERVER IP>/cblr/svc/op/ks/profile/LiveCD
>         ipappend 2
>
> On Thu, Dec 28, 2017 at 12:12 PM, Locane <address@hidden> wrote:
>
>    The grub entry looks like this currently:
>
>    menuentry 'Do not use broken livecd' {
>       linuxefi images/LiveCD/vmlinuz initrd=images/LiveCD/initrd.img ksdevice=
>    bootif lang=  root=live:/boot.iso kssendmac text  ks=http://<SERVER IP>/
>    cblr/svc/op/ks/profile/LiveCD
>       initrdefi images/LiveCD/initrd.img
>    }
>
>    On Thu, Dec 28, 2017 at 12:09 PM, Randy Goldenberg <
>    address@hidden> wrote:
>
>        On Wednesday December 27, 2017, Locane wrote:
>
>            Hello all!  I hope this is the appropriate list for Grub2
>            questions, if not
>            please let me know.
>
>            As a self-taught DevOps person, I'm missing some knowledge.
>
>            At the moment, I'm trying to boot a 1.2 gigabyte CentOS 7.4 livecd
>            from an
>            EFI PXE menu using grubx64.efi, and I'm running in to the error
>            "Cannot
>            allocate initrd".
>
>
>        How have you configured grub for booting the live CD?
>
>        Thanks,
>
>        Randy
>
>        _______________________________________________
>        Help-grub mailing list
>        address@hidden
>        https://lists.gnu.org/mailman/listinfo/help-grub