Modern GRUBing: Difference between revisions
Created page with "Rocky Linux 9 does not use the /etc/default/grub and /boot/grub2/grub.cfg Files any longer. Instead the BLS (Boot Loader Specification) 'method' is used. If one reads the documentation from RedHat, it seems like thing got really messy (and confusing). ==== BLS (Boot Loader Specification) ==== /etc/fstab grub2-mkconfig -o /tmp/boot/grub2/grub.cfg --root-directory=/tmp/LV.ROOT ==== GRUB "Installation" for MBR / BIOS ==== Installs the Stage 1 Boot Code (program) in..." |
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Notes; | |||
*LVM on NVMe is the issue | |||
Rocky Linux 9 does not use the /etc/default/grub and /boot/grub2/grub.cfg Files any longer. Instead the BLS (Boot Loader Specification) 'method' is used. If one reads the documentation from RedHat, it seems like thing got really messy (and confusing). | Rocky Linux 9 does not use the /etc/default/grub and /boot/grub2/grub.cfg Files any longer. Instead the BLS (Boot Loader Specification) 'method' is used. If one reads the documentation from RedHat, it seems like thing got really messy (and confusing). | ||
====Quick D for Cloning, err, "Recreating" a drive from a BackUp (IE, the closest thing to Acronis that Linux seems to have)==== | |||
*Create a duplicate or functionally similar Partition layout to the original | |||
**CFDISK and "Logical Volume Commands" | |||
**Use Blivet from a Rocky 8 Live Boot Device<br /> | |||
====Rough D==== | |||
*Start from a 'Clean Slate': <code>wipefs -a /dev/sdX</code> (make dang sure the proper 'sdX' is chosen!) | |||
*Set the Partition Type (MBR or GPT): <code>cfdisk /dev/sdX</code>, (select DOS or GPT, save it (write) ) | |||
*Create Partitions: cfdisk | |||
**https://en.wikipedia.org/wiki/Partition_type | |||
**Linux EXT4: $83 (that's Commodore Speaky for 83h) | |||
**Linux LVM (and LVM2): $8E | |||
*LVM Stuff using Commands or BLIVET (sadly only Rocky Linux 8) | |||
**<code>pvcreate /dev/sdXy</code> | |||
**<code>vgcreate VG.NVMe.ROOT /dev/sdXy</code> | |||
***<code>vgrename WhatEverOldName WhatEverNewName</code> | |||
**<code>lvcreate -L 64G -n LV.ROOT VG.NVMe.ROOT</code> | |||
*Format Partitions | |||
**mkfs.vfat -F32 /dev/sdXy | |||
**<code>mkfs.ext4 -v -L ROOT.EXT4 /dev/sdXy ( -v = Verbose, -L = Label )</code> | |||
**<code>mkswap -L SWAP /dev/sdaXy</code> | |||
*MBR Stuff if desired | |||
*UEFI Stuff ("make" the grubx64.efi File) --- Best done from a UEFI system! | |||
**grub2-mkstandalone is a similar command | |||
**Make sure UEFI Stuff is installed (if cloning from an MBR / BIOS based system); | |||
***dnf install grub2-efi-x64 grub2-tools grub2-tools-efi grub2-tools-extra grub2-efi-x64-modules efibootmgr shim-x64 | |||
**<code>mkdir /mnt/efi</code> | |||
**<code>mount /dev/nvme0n1p1 /mnt/efi</code> | |||
**<code>grub2-install --target=x86_64-efi --efi-directory=/mnt/efi --bootloader-id=rocky --recheck --force --verbose --modules="part_gpt ext2 fat normal search search_fs_uuid search_fs_file configfile all_video gfxterm gzio" **--no-nvram** **--removable**</code> | |||
***--force = Do it on a supposedly 'non-secure' system | |||
***--no-nvram = Do it even if a target drive is being prepared as a UEFI Booted system even if the current OS is an MBR / BIOS system | |||
***--removable is optional and installs the 'generic' BOOTX64.EFI File. ) | |||
***--modules because apparently absolutely no modules are installed by default, even ext2! | |||
****...and if you've got loads of space, then load up grubx64.efi with everything: --modules="$(ls /boot/grub2/x86_64-efi/ | sed 's/\.mod//g' | tr '\n' ' ')" | |||
**Command to show information on how a system was booted (and can boot): <code>bootctl status</code> | |||
**Command for EFIBootMgr: <code>efibootmgr -v</code> | |||
*GRUB Menu stuff | |||
**Edit: /etc/default/grub | |||
**Make the grub.cfg file: grub2-mkconfig -o /boot/grub2/grub.cfg | |||
**Seemingly useless command (as a text editor would work, no matter the 'threats' in the file): grub2-editenv | |||
***Wait, spoke too soon. If this error is encountered: grub2-editenv: error: environment block too small. when using kernel-install it indicates the grubenv file isn't 1024 bytes. Seems like the grub2-editenv tool pads the file with ###### symbols to make it exactly 1024 Bytes (and we know how important it is to have a file equal to exactly 1024 Bytes!) | |||
**grub2-probe: General information, simple | |||
*Kernel Stuff (initramfs, vmlinuz, bootloader entries, etc.): kernel-install | |||
**to 'redo' VMLinuz Stuff: dracut | |||
*Edit / Register the entry in the Hardwares UEFI Storage space | |||
**efibootmgr --create --disk /dev/nvme0n1 --part 1 --loader '\EFI\rocky\grubx64.efi' --label "Custom GRUB" --bootorder 0001 | |||
*Edit the BLS (Boot Loader System) Entries, etc. | |||
**GRUBBY | |||
*Restore BOOT and ROOT File Systems | |||
**f | |||
**f | |||
*Modify Entries in; | |||
**/boot/loader/entries (wherever mounted) | |||
**/etc/fstab (wherever mounted) | |||
*...and the tribulations continue as the below command won't work from an MBR / BIOS system or theoretically from any system that isn't the one being booted, run from etc.; | |||
**Entry for Hardware Firmware (AKA BIOS Settings): efibootmgr --create --disk /dev/sdb --part 1 --loader /EFI/rocky/grubx64.efi --label "Rocky Linux" --verbose | |||
**Work Around: | |||
==== BLS (Boot Loader Specification) ==== | ====BLS (Boot Loader Specification)==== | ||
Nope, not anymore (sort of): /etc/fstab | |||
/ | Nope, not anymore (sort of): grub2-mkconfig -o /tmp/boot/grub2/grub.cfg --root-directory=/tmp/LV.ROOT | ||
Look in /boot/loader/entries and / or use GRUBBY | |||
...see below for key information on /etc/default/grub and BLS | |||
==== GRUB "Installation" for MBR / BIOS ==== | ====GRUB "Installation" for MBR / BIOS==== | ||
Installs the Stage 1 Boot Code (program) in the MBR and Stage 1.5 Boot Code (program) in the "MBR Gap": grub2-install --target=i386-pc /dev/sdd | Installs the Stage 1 Boot Code (program) in the MBR and Stage 1.5 Boot Code (program) in the "MBR Gap": grub2-install --target=i386-pc /dev/sdd | ||
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Use DD to clone the Boot Partition | Use DD to clone the Boot Partition | ||
==== Sources ==== | ====Sources==== | ||
https://www.baeldung.com/linux/grub-menu-management | https://www.baeldung.com/linux/grub-menu-management | ||
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https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/9/html/managing_monitoring_and_updating_the_kernel/configuring-kernel-command-line-parameters_managing-monitoring-and-updating-the-kernel | https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/9/html/managing_monitoring_and_updating_the_kernel/configuring-kernel-command-line-parameters_managing-monitoring-and-updating-the-kernel | ||
==== ChatGPT's Opinion ==== | ====ChatGPT's Opinion==== | ||
===== GRUB "Installation" ('''What Does <code>grub2-install</code> Do?)''' ===== | =====GRUB "Installation" ('''What Does <code>grub2-install</code> Do?)'''===== | ||
The <code>grub2-install</code> command is used to '''install''' the '''GRUB bootloader''' onto a disk or partition. It places the necessary GRUB '''boot code''' onto the target disk and copies GRUB modules required for booting. | The <code>grub2-install</code> command is used to '''install''' the '''GRUB bootloader''' onto a disk or partition. It places the necessary GRUB '''boot code''' onto the target disk and copies GRUB modules required for booting. | ||
====== '''How <code>grub2-install</code> Works''' ====== | ======'''How <code>grub2-install</code> Works'''====== | ||
When executed, <code>grub2-install</code> performs the following actions: | When executed, <code>grub2-install</code> performs the following actions: | ||
'''1. Determines the Installation Target''' | '''1. Determines the Installation Target''' | ||
* If given a disk (e.g., <code>/dev/sda</code>), it installs '''GRUB to the MBR or GPT boot partition'''. | *If given a disk (e.g., <code>/dev/sda</code>), it installs '''GRUB to the MBR or GPT boot partition'''. | ||
* If given a partition (e.g., <code>/dev/sda1</code>), it may fail or install to the '''partition's boot sector''' (not recommended). | *If given a partition (e.g., <code>/dev/sda1</code>), it may fail or install to the '''partition's boot sector''' (not recommended). | ||
* If on a '''BIOS system''', it installs the <code>i386-pc</code> GRUB bootloader. | *If on a '''BIOS system''', it installs the <code>i386-pc</code> GRUB bootloader. | ||
* If on a '''UEFI system''', it installs <code>x86_64-efi</code> and places EFI files in the EFI system partition. | *If on a '''UEFI system''', it installs <code>x86_64-efi</code> and places EFI files in the EFI system partition. | ||
'''2. Copies GRUB Core to the Correct Location''' | '''2. Copies GRUB Core to the Correct Location''' | ||
* On '''BIOS/MBR systems''', GRUB places its '''boot code''' in the MBR and additional code in the '''post-MBR gap''' (sectors after the MBR). | *On '''BIOS/MBR systems''', GRUB places its '''boot code''' in the MBR and additional code in the '''post-MBR gap''' (sectors after the MBR). | ||
* On '''GPT systems using BIOS (BIOS-GPT)''', it places GRUB in the '''BIOS Boot Partition'''. | *On '''GPT systems using BIOS (BIOS-GPT)''', it places GRUB in the '''BIOS Boot Partition'''. | ||
* On '''UEFI systems''', it installs the <code>grubx64.efi</code> file into the '''EFI System Partition (ESP)'''. | *On '''UEFI systems''', it installs the <code>grubx64.efi</code> file into the '''EFI System Partition (ESP)'''. | ||
'''3. Selects the Correct GRUB Modules''' | '''3. Selects the Correct GRUB Modules''' | ||
* <code>grub2-install</code> determines which GRUB modules are needed based on the filesystem, partition layout, and system firmware. | *<code>grub2-install</code> determines which GRUB modules are needed based on the filesystem, partition layout, and system firmware. | ||
* It installs these modules into <code>/boot/grub2/</code> (BIOS) or <code>/boot/efi/EFI/</code> (UEFI). | *It installs these modules into <code>/boot/grub2/</code> (BIOS) or <code>/boot/efi/EFI/</code> (UEFI). | ||
'''4. Writes GRUB Boot Code''' | '''4. Writes GRUB Boot Code''' | ||
* '''BIOS (MBR) Installation:''' | *'''BIOS (MBR) Installation:''' | ||
** The '''Stage 1 boot code''' is written into the MBR. | **The '''Stage 1 boot code''' is written into the MBR. | ||
** The '''Stage 1.5 boot code''' is stored in the post-MBR gap (if available). | **The '''Stage 1.5 boot code''' is stored in the post-MBR gap (if available). | ||
** The '''Stage 2 boot code''' (GRUB core modules) is stored in <code>/boot/grub2/</code>. | **The '''Stage 2 boot code''' (GRUB core modules) is stored in <code>/boot/grub2/</code>. | ||
* '''UEFI Installation:''' | *'''UEFI Installation:''' | ||
** The <code>grubx64.efi</code> file is copied to the EFI System Partition. | **The <code>grubx64.efi</code> file is copied to the EFI System Partition. | ||
** GRUB is registered as a boot entry with the system's UEFI firmware. | **GRUB is registered as a boot entry with the system's UEFI firmware. | ||
'''5. Registers the Bootloader (If UEFI)''' | '''5. Registers the Bootloader (If UEFI)''' | ||
* On '''UEFI systems''', <code>grub2-install</code> registers <code>grubx64.efi</code> with the UEFI boot manager using <code>efibootmgr</code>. | *On '''UEFI systems''', <code>grub2-install</code> registers <code>grubx64.efi</code> with the UEFI boot manager using <code>efibootmgr</code>. | ||
===More from ChatGPT on "GRUBing"=== | |||
='''Comprehensive Guide to Installing GRUB on Rocky Linux (UEFI & BIOS)'''= | |||
This guide covers: | |||
*'''UEFI bootloader installation''' on a target drive. | |||
*'''Legacy BIOS (MBR) bootloader installation'''. | |||
*'''BLS (Boot Loader Specification) and its effect on <code>grub2-mkconfig</code>.''' | |||
*'''GRUB Boot Stages Explanation (Stage 1, Stage 1.5, Stage 2).''' | |||
*'''How to properly configure bootloader entries and verify installation.''' | |||
---- | |||
=='''1. Understanding GRUB Boot Stages'''== | |||
{| class="wikitable" | |||
!'''GRUB Stage''' | |||
!'''Description''' | |||
!'''Applies To''' | |||
|- | |||
|'''Stage 1''' | |||
|'''MBR code''' (first 512 bytes of disk) loads Stage 1.5 or Stage 2. | |||
|'''Legacy BIOS (MBR) Only''' | |||
|- | |||
|'''Stage 1.5''' | |||
|Located in the first 30KB after MBR, it helps find <code>/boot/grub2</code>. | |||
|'''Legacy BIOS (MBR) Only''' | |||
|- | |||
|'''Stage 2''' | |||
|Loads the GRUB menu, kernel, and initrd. | |||
|'''Both UEFI and BIOS''' | |||
|- | |||
|'''UEFI Firmware Boot''' | |||
|Uses the '''EFI System Partition (ESP)''' instead of MBR. Loads <code>grubx64.efi</code>. | |||
|'''UEFI Only''' | |||
|} | |||
---- | |||
=='''2. Installing GRUB for UEFI Booting'''== | |||
==='''A. Identify the Target Drive'''=== | |||
List available drives and partitions: | |||
Look for the '''EFI System Partition (ESP)''', usually '''formatted as FAT32 (<code>vfat</code>)'''. | |||
Example: If the target drive is <code>/dev/sdb</code>, and the EFI partition is <code>/dev/sdb1</code>, mount it: | |||
==='''B. Bind System Directories (for Chroot)'''=== | |||
If configuring an external system: | |||
==='''C. Install Required UEFI GRUB Packages'''=== | |||
==='''D. Install GRUB to the Target Drive'''=== | |||
*<code>--target=x86_64-efi</code> → Specifies '''UEFI mode'''. | |||
*<code>--efi-directory=/boot/efi</code> → Ensures GRUB is installed in the EFI partition. | |||
*<code>--bootloader-id=rocky</code> → Labels the boot entry as '''"Rocky"'''. | |||
*<code>--recheck</code> → Forces a re-scan of the drive layout. | |||
==='''E. Generate the GRUB Configuration'''=== | |||
⚠ '''However, Rocky Linux follows BLS, which makes this step less critical''' (explained in Section 4). | |||
---- | |||
=='''3. Installing GRUB for Legacy BIOS (MBR Boot)'''== | |||
==='''A. Mount the Target Drive's Root Partition'''=== | |||
If the system has a separate <code>/boot</code> partition: | |||
==='''B. Chroot into the Target System'''=== | |||
==='''C. Install Required BIOS GRUB Packages'''=== | |||
==='''D. Install GRUB to the MBR of the Target Drive'''=== | |||
*<code>--target=i386-pc</code> → '''Required for Legacy BIOS (MBR) booting'''. | |||
*<code>/dev/sdb</code> → '''Must be the whole disk (not a partition like <code>/dev/sdb1</code>)'''. | |||
*<code>--recheck</code> → Forces a disk layout rescan. | |||
==='''E. Generate the GRUB Configuration'''=== | |||
⚠ '''But due to BLS, <code>grub.cfg</code> is no longer the main configuration source.''' | |||
---- | |||
=='''4. Understanding BLS (Boot Loader Specification)'''== | |||
Rocky Linux follows '''BLS (Boot Loader Specification)''', meaning '''boot entries are controlled by systemd-boot entries, not <code>grub2-mkconfig</code>'''. | |||
==='''How to Manually Manage BLS Entries'''=== | |||
#'''List Existing Boot Entries:''' | |||
#'''Manually Create a BLS Entry:''' | |||
#'''Example BLS Entry (<code>rocky.conf</code>)''' | |||
#'''Enable BLS Support in GRUB (if needed)''' | |||
==='''Why BLS Makes <code>grub2-mkconfig</code> Less Relevant'''=== | |||
*'''Traditional GRUB entries are no longer used''' in Rocky Linux. | |||
*The '''bootloader reads BLS entries instead'''. | |||
*'''<code>grub.cfg</code> is still used for bootloader settings''', but '''kernel entries are controlled by BLS'''. | |||
---- | |||
=='''5. Verify Installation'''== | |||
==='''Check EFI Boot Entries (For UEFI Only)'''=== | |||
==='''Check GRUB Installation'''=== | |||
==='''Check BLS Entries'''=== | |||
==='''Reboot and Test'''=== | |||
---- | |||
=='''6. Summary'''== | |||
{| class="wikitable" | |||
!'''Boot Mode''' | |||
!'''Target Option for GRUB''' | |||
!'''Install Command''' | |||
!'''Config Location''' | |||
|- | |||
|'''UEFI''' | |||
|<code>x86_64-efi</code> | |||
|<code>grub2-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=rocky</code> | |||
|<code>/boot/efi/EFI/rocky/grub.cfg</code> | |||
|- | |||
|'''BIOS (MBR)''' | |||
|<code>i386-pc</code> | |||
|<code>grub2-install --target=i386-pc /dev/sdb</code> | |||
|<code>/boot/grub2/grub.cfg</code> | |||
|- | |||
|'''BLS (Rocky Linux Default)''' | |||
|<code>systemd-boot controlled</code> | |||
|<code>bootctl list</code> | |||
|<code>/boot/loader/entries/</code> | |||
|} | |||
<br /> | <br /> | ||
=='''1. The Presence (or Absence) of <code>/boot/grub2/grub.cfg</code>'''== | |||
*If '''<code>grub.cfg</code> exists''', GRUB will parse it. | |||
*If '''<code>grub.cfg</code> does NOT exist''', GRUB will attempt to '''read the BLS entries directly''' instead. | |||
This means: | |||
✔ '''Deleting <code>grub.cfg</code> forces GRUB to rely entirely on BLS.''' | |||
✔ '''Regenerating <code>grub.cfg</code> (<code>grub2-mkconfig</code>) puts GRUB back into a "hybrid mode" where it may still reference BLS but also maintain compatibility with legacy boot setups.''' | |||
---- | |||
=='''2. GRUB’s Bootloader Installation (<code>grub2-install</code>)'''== | |||
The actual bootloader installed to the disk controls whether it defaults to '''BLS mode or <code>grub.cfg</code> mode'''. | |||
When GRUB is installed with: | |||
(''where <code>/dev/sdX</code> is your boot disk, like <code>/dev/sda</code> or <code>/dev/nvme0n1</code>''), it does the following: | |||
*Sets up '''GRUB’s core image''' (<code>/boot/grub2/i386-pc/core.img</code> for BIOS systems or <code>/boot/efi/EFI/rocky/grubx64.efi</code> for UEFI systems). | |||
*Embeds the logic for '''how GRUB will find and load boot entries'''. | |||
*If BLS is active, it instructs GRUB to '''skip parsing <code>grub.cfg</code> and go directly to BLS entries'''. | |||
This means: ✔ If GRUB was installed '''with BLS enabled''', even if <code>grub.cfg</code> exists, it may not be used. | |||
✔ If GRUB was installed '''without BLS support''', it will fall back to <code>grub.cfg</code>. | |||
---- | |||
=='''How to Explicitly Switch Between BLS and <code>grub.cfg</code>'''== | |||
==='''To Force BLS Mode (and Ignore <code>grub.cfg</code> Completely)'''=== | |||
#'''Ensure BLS entries exist''': If this folder is empty, something is broken. | |||
#'''Delete <code>grub.cfg</code>''' (this ensures GRUB won’t use it): | |||
#'''Ensure GRUB is installed with BLS support''': ''(For UEFI systems; adjust for BIOS if needed.)'' | |||
#'''Reboot''' and verify that <code>grub.cfg</code> is no longer in use. | |||
---- | |||
==='''To Force Legacy <code>grub.cfg</code> Mode (and Ignore BLS)'''=== | |||
#'''Ensure <code>grub.cfg</code> is present''': | |||
#'''Reinstall GRUB to disable BLS mode''': ''(The <code>--no-bootloader-spec</code> flag explicitly prevents GRUB from using BLS.)'' | |||
#'''Reboot''' and verify that <code>grub.cfg</code> is being used. | |||
---- | |||
==='''Final Answer'''=== | |||
✔ '''The real switch between BLS and <code>grub.cfg</code> is NOT in <code>/etc/default/grub</code>—it's controlled by how GRUB is installed and configured.''' | |||
✔ '''Deleting <code>grub.cfg</code> forces BLS mode, provided GRUB was installed with BLS support.''' | |||
✔ '''Reinstalling GRUB with <code>--no-bootloader-spec</code> forces it to use <code>grub.cfg</code> instead of BLS.''' | |||
✔ '''To change modes, you must either delete <code>grub.cfg</code> (to force BLS) or reinstall GRUB (to force legacy mode).''' | |||