Thanks for the detail Pascal.
On Tue, Sep 15, 2015 at 2:00 AM, Pascal Hambourg <pas...@plouf.fr.eu.org> wrote: > Muhammad Yousuf Khan a écrit : > > command "grub-install --modules=part_gpt /dev/sdc" resolved the issue for > > me. > > Glad to hear it. > > > however i also wanted to know that how it actually works. > > what is the difference. i can understand i am mentioning gpt module in > > the command but what is the theoretical story behind this to work. or > > what is the difference b/w grub-install /dev/sdc and grub-install > > --modules=part_gpt /dev/sdc > > A typical GRUB boot loader comes in 2 or 3 parts : > 1) A "boot image" installed in the boot sector of a disk (MBR) or a > partition (PBR). Not used for EFI boot. > 2) A "core image" installed either in a special place outside a > filesystem (gap between the MBR and 1st partition in a MSDOS format > disk, BIOS boot partition in a GPT format disk) or as a regular file in > a filesystem, /boot/grub/core.img or /boot/grub/i386-pc/core.img for PC > BIOS, or /boot/efi/EFI/debian/grubx64.efi for UEFI. > 3) Various files in /boot/grub/, including the config file grub.cfg and > modules. > > The BIOS firmware loads the boot image which loads the core image, or > the EFI firmware loads directly the core image. Then the core image > reads files in /boot/grub to display the boot menu, then reads files in > /boot/grub and other locations to boot the selected entry. > > The boot image uses block lists to load the core image, so it does not > have to understand partition tables, filesystems or whatever. But the > core image read files, so it has to understand the filesystem, partition > table, RAID array or LVM volume these files reside in. GRUB modules are > just like Linux kernel modules : they provide loadable capabilities to > the core image (~ GRUB kernel) to read filesystems such as ext2/3/4, > btrfs, NTFS, FAT, containers such as LVM or RAID, partition tables such > as GPT or MSDOS and so on. The purpose of this modular design is to keep > the core image small, otherwise it may not fit into the post-MBR gap > (previously 31 KiB, now 1 MiB). But modules are files, and the core > image must be able to load them before it can use their capabilities. So > the required modules to read files in /boot/grub must be embedded into > the core image. grub-install is supposed to auto-detect all needed > modules and include them when building the core image. However, it seems > that in your case it didn't. Maybe it was confused by the presence of > both MSDOS and GPT partition tables. The --modules option instructed > grub-install to include the module providing the missing capability to > read GPT partition tables. > >
