USB ISO For CentOS 8

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I did the dd of the ISO to a 16G USB device.

the second partition is FAT so I can edit it – I want to make a custom menu entry. I edited the grub.cfg – but that did not work – my menu option does not show.

Then I think I need to change BOOT.cfg and generate the grub.cfg – but I
dont know in this case how to generate for the USB device.

What command do I use for that ?
Thanks,

Jerry

4 thoughts on - USB ISO For CentOS 8

  • You will want to follow the instructions for creating a custom .iso

    https://access.redhat.com/solutions/60959
    ^^^ Requires a Red Hat account, or Red Hat Developer Account.

    The keys are to modify both:

    – /isolinux/isolinux.cfg – for legacy BIOS boot
    – /EFI/BOOT/grub.cfg – for UEFI boot

    Make sure not to change the Volume Label, as this can mess up the UEFI boot

    Then generate the .iso:

    # cd /tmp/rhel7/
    # mkisofs -o /tmp/rhel7test.iso -b isolinux/isolinux.bin -J -R -l -c isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table -eltorito-alt-boot -e images/efiboot.img -no-emul-boot -graft-points -V “RHEL-7.7 Server.x86_64” .

    ^^^ Change the “-V” label accordingly for CentOS 8 to match the CentOS 8 disk label.

    And the critical command for USB drive booting:

    # isohybrid –uefi /tmp/rhel7test.iso

    Gregory Young

    —–Original Message—

  • If you boot via UEFI, you need to edit differnt grub.cfg, EFI/BOOT/grub.cfg not isolinux/grub.cfg

  • isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table
    -eltorito-alt-boot -e images/efiboot.img -no-emul->boot -graft-points -V
    “RHEL-7.7 Server.x86_64” .

    disk label.

    I was “thinking” all that was not needed – the second partition is
    “editable” – I change the file – I just need to regenerate grub right – not the whole ISO. I was hoping that is why they split this out into two partitions – for just such an occasion? Just want to add a menu option.

    THanks,

    Jerry

  • Nope, that editable FAT partition is actually the EFI boot partition. IIRC, the grub config in that partition isn’t actually used, only the EFI bootstrap files. Once it can access the config on the main .iso partition it loads everything from there.

    Gregory Young

    —–Original Message—