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Talaat Etman
Asked: 2024-07-28 05:26:58 +0800 CST

how to solve the USB flash drive grub files without reinstalling the grub bootloader?

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The problem:

The USB flash drive takes alot of time to install grub bootloader, now the grub bootloader is installed in the MBR, but the /boot/grub/* files may be missed or corrupted or deleted acdently, and may be a solution that is used as useful way without the need to reinstall the bootloader.

The aim:

Regenerate /boot/grub/* files.

The question:

What are the commands needed to regenerate /boot/grub/i386-pc/* files and /boot/grub/grubenv except grub.cfg file in a fatest fashion?

boot

1 Answers

  1. Best Answer

    Solve the USB flash drive grub files without reinstalling the grub bootloader

    GRUB comes with boot images, which are normally put in the directory /usr/lib/grub/<cpu>-<platform> (for BIOS-based machines /usr/lib/grub/i386-pc). Hereafter, the directory where GRUB images are initially placed (normally /usr/lib/grub/<cpu>-<platform>) will be called the image directory, and the directory where the boot loader needs to find them (usually /boot) will be called the boot directory.

    To regenerate a new image directory (/boot/grub/i386-pc), we assume that the USB flash drive takes /dev/sdc1 and this commands will be applied:

    sudo mount /dev/sdc1 /mnt/sdc1
sudo mv /mnt/sdc1/boot/grub /mnt/sdc1/boot/grub.old
sudo cp -a /usr/lib/grub/i386-pc /mnt/sdc1/boot/grub/i386-pc

    After these commands are applied, the USB flash drive was mmounted in /mnt/sdc1, the existing /boot/grub directory in the USB flash drive was renamed to /boot/grub.old, and the overall /usr/lib/grub/i386-pc directory was copied to /boot/grub/i386-pc directory of the USB flash drive. We don't need all of the files included in the directory, but the directory will have a small amount of size. the most important thing is we still need to generate the missed file /i386-pc/core.img.

    core.img, this is the core image of GRUB. It is built dynamically from the kernel image and an arbitrary list of modules by the grub-mkimage program. Usually, it contains enough modules to access /boot/grub, and loads everything else (including menu handling, the ability to load target operating systems, and so on) from the file system at run-time. The modular design allows the core image to be kept small, since the areas of disk where it must be installed are often as small as 32KB.

    To generate /i386-pc/core.img the following command will be applied:

    sudo grub-mkimage --output=/tmp/core.img --prefix=/dev/sdc1/boot/grub --format=i386-pc biosdisk part_msdos NTFS

    Now the /core.img is placed in /tmp directory. if this command is not worked, try the following instead:

    sudo grub-mkimage --output=/tmp/core.img --prefix=/mnt/sdc1/boot/grub --format=i386-pc biosdisk part_msdos NTFS

    Copy the /tmp/core.img to /i386-pc/core.img in the USB flash drive:

    sudo cp -R /tmp/core.img /mnt/sdc1/i386-pc/core.img

    The latest file is /boot/grub/grubenv.

    The GRUB environment block, it is often useful to be able to remember a small amount of information from one boot to the next. For example, you might want to set the default menu entry based on what was selected the last time. GRUB deliberately does not implement support for writing files in order to minimise the possibility of the boot loader being responsible for file system corruption, so a GRUB configuration file cannot just create a file in the ordinary way. However, GRUB provides an “environment block” which can be used to save a small amount of state.

    The environment block is a preallocated 1024-byte file, which normally lives in /boot/grub/grubenv (although you should not assume this). At boot time, the load_env command (see load_env) loads environment variables from it, and the save_env (see save_env) command saves environment variables to it. From a running system, the grub-editenv utility can be used to edit the environment block.

    For safety reasons, this storage is only available when installed on a plain disk (no LVM or RAID), using a non-checksumming filesystem (no ZFS), and using BIOS or EFI functions (no ATA, USB or IEEE1275).

    The command needed is:

    sudo grub-editenv /mnt/sdc1/boot/grub/grubenv create

    this command while create an emptygrubenv file, and allow you to continue without the error:

    Error: invalid environment block.
press any key to continue....

    The latest thing to do is copy grub.cfg file from /grub.old directory, or create a new one, and reboot to test the USB flash drive boot process.

    GNU GRUB Manual 2.12

    How to Move, Copy, and Rename a Directory in Linux

    GRUB Error 'invalid environment block' on booting & updating Ubuntu

    Generate core.img file

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