converting CSM (legacy) bootable ISOs to UEFI bootable ISOs

[paresh]

Is it possible to modify a CSM (legacy) bootable iso to a UEFI or CSM and UEFI bootable ISO for use with Ventoy?

If yes where can i find detailed instructions for the same?

Many Thanks

[Premiere]

Yes and it's not that difficult.
Although it's hard to find a clear explanation.
The source code this software contains code that I have just altered to do just this and solved a long gave up upon sought after method to make my ISO not use isolinux and still use grub instead. Look at the LiveCD source code.
When I perfect a script to do this automatically I will post it.

[paresh]

Please do let me know.

[Premiere]

Please do let me know.

Let me try and explan.

You need Linux, preferably an Ubuntu based 
You need to install xorriso 
I think that automatically installs mkisofs 
Hopefully you know a bit about boot files.
You need to look at the configuration files in the legacy 
Iso's .

If it's using isolinux or grub. 
for isolinux you will need to translate everything 
Into grub.cfg format, I wish there was a tool to do this,  I have yet to find one, it does seem like it would be hard to program one.

if your booting non free software this may be very difficult I haven't Done anything but windows 10. 

You should be able to just copy over the efi / EFI directory and the efi.img nomaly located in the grub folder from a similar iso to this rebuild  one you will need to make.

If not you will need to make one then build a fat image and c
REMEMBER TO KEEP THE FOLDER STRUCTURE THE SAME
Or it will not be able to find your configuration file.

You need to make a Folder with all contents of the ISO
You need to rebuild it with the xorriso utility.

example: Any questions.... Still working on a script. It can be made a lot more simple.
ISOLinux
xorriso -as mkisofs -volid "ZZZZ" -iso-level 3 -isohybrid-mbr /usr/lib/ISOLINUX/isohdpfx.bin -c isolinux/boot.cat -b isolinux/isolinux.bin -no-emul-boot -boot-load-size 4 -boot-info-table -eltorito-alt-boot -e boot/grub/efi.img -no-emul-boot -isohybrid-gpt-basdat -o /media/zorin/ToySSD/zorin-livecdISOlinux.iso ./ISO

GRUB2
xorriso -as mkisofs -volid "What should I BE Called" -iso-level 3 -b boot/grub/cdrom.img --grub2-boot-info --grub2-mbr ./GRUB/boot_hybrid.img -c boot/grub/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table -eltorito-alt-boot -e boot/grub/efi.img -no-emul-boot -append_partition 2 0xEF ./ISO/boot/grub/efi.img -o /YOUR.iso ./FOLDERwithISOfiles

This is in the source code They are commented out so they dont get executed . but they can be used to build a new EFI image : You still need to make a fat image and copy them
The lazy way is to remove the last line in the /LiveCd/livecd.sh so it does not remove the ISO_TMP the efi.img fat image will be in there also The embed.cfg points to the config file locatation.

The --prefix '/efi/boot' < your boot location is all that may need to be changed. this command can not be ran on its own needs the full lists of modules.
grub-mkimage -v --directory "$VT_DIR/GRUB2/INSTALL/lib/grub/x86_64-efi" -c "$VT_DIR/LiveCD/GRUB/embed.cfg" --prefix '/efi/boot' --output "$VT_DIR/LiveCD/GRUB/bootx64.efi" --format 'x86_64-efi' --compression 'auto' $all_modules_uefi 'fat' 'part_msdos'

grub-mkimage -v --directory "$VT_DIR/GRUB2/INSTALL/lib/grub/i386-pc" -c "$VT_DIR/LiveCD/GRUB/embed.cfg" --prefix '/boot/grub' --output "$VT_DIR/LiveCD/GRUB/cdrom.img" --format 'i386-pc-eltorito' --compression 'auto' $all_modules_legacy 'biosdisk' 'iso9660' 'fat' 'part_msdos'
rm -f $VT_DIR/LiveCD/GRUB/boot_hybrid.img
cp -a $VT_DIR/GRUB2/INSTALL/lib/grub/i386-pc/boot_hybrid.img $VT_DIR/LiveCD/GRUB/boot_hybrid.img

[paresh]

@Premiere Thank you so very much for such an elaborate reply.

[Premiere]

Your welcome
By the way if it's Linux stuff you can most likely combine two or more cds into one I boot off of a 9+Gb iso from ventoy. You can boot from a multi boot ios .

[paresh]

Your welcome
By the way if it's Linux stuff you can most likely combine two or more cds into one I boot off of a 9+Gb iso from ventoy. You can boot from a multi boot ios .

Thanks once again.

[perfection]

I always thought you could create a bootable UEFI USB drive (with say Rufus) and lift the image and use it in Ventoy....

Would that work?