Featured image of post Multi-System Boot Loader Configuration
Software

Multi-System Boot Loader Configuration

This article introduces the configuration of multi-system boot loader, including the settings of boot loader, EFI/Grub/rEFInd, and how to customize the theme of multi-system boot loader.

Motivation

I have installed dual or multiple systems on my computer before, but I have always been confused about the boot entries of multiple systems, often encountering problems such as missing boot entries and duplicate boot entries. This time I plan to study the configuration of multi-system boot entries in depth, including the settings of boot loaders, EFI/Grub/rEFInd, and how to customize the theme of multi-system boot loaders.

Operating System Boot Process

The computer boot process is mainly divided into 4 steps: 1. Power on; 2. BIOS/UEFI boot; 3. Load boot entries; 4. Operating system boot. Steps 1 and 4 generally do not require user intervention, while steps 2 and 3 require user configuration. So here we mainly introduce the content of steps 2 and 3.

Computer Boot Process

BIOS/UEFI Boot

BIOS (Basic Input/Output System) and UEFI (Unified Extensible Firmware Interface) are the firmware of the computer, responsible for booting the computer and loading the operating system. BIOS is the old boot method, and UEFI is the new boot method, UEFI has more functions and better performance than BIOS. Whether UEFI or BIOS, they are firmware on the motherboard.

BIOS Boot Process

BIOS is generally used on older computers, and its boot process is relatively fixed, with low user customization. It is mainly divided into the following steps:

  1. BIOS POST (Power-On Self-Test) self-test

  2. BIOS reads the boot program in the MBR (Master Boot Record)

  3. The boot program reads the partition table and finds the active partition

  4. The boot program reads the boot sector of the active partition and loads the operating system

The location of the MBR is fixed, generally in the first sector of the hard disk, with a size of 512 bytes. The MBR contains the partition table and the boot program, the partition table records the partition information of the hard disk, and the boot program is responsible for loading the operating system.

UEFI Boot Process

UEFI is also a kind of BIOS, generally used on newer computers. Its boot process is more flexible, with more functions and higher user customization. Although UEFI has more functions, its process is more unified, mainly divided into the following steps:

  1. UEFI POST (Power-On Self-Test) self-test

  2. UEFI reads the boot program in the EFI partition

  3. The boot program reads the boot file in the EFI partition and loads the operating system

UEFI Interface of ASUS Motherboard

Compared with BIOS, UEFI uses the EFI partition, and the location of the EFI partition is not fixed, and there can even be multiple EFI partitions on one hard disk.

The boot program and boot file of UEFI are stored in the EFI partition, including the boot program, boot file, driver program, etc. As long as the boot file meets the UEFI specification, whether it is the boot program of Windows, Linux, or macOS, and no matter where the boot file is placed in the EFI partition, UEFI can find and load it.

Since UEFI is more flexible and updated, the following multi-system boot entry configuration is based on UEFI.

Concept Distinction: Boot Loader, Boot Entry, Boot File

Before discussing the configuration of multi-system boot entries, let’s first sort out the concepts of boot loader, boot entry, and boot file.

  1. Boot Loader: Responsible for loading the operating system’s boot program, each boot program is a boot entry. Common boot loaders include Grub (Grub2), rEFInd, Clover, etc.

  2. Boot Entry: Each operating system loaded by the boot loader is a boot entry, and each boot entry corresponds to an operating system. The boot entry contains the operating system’s boot file, kernel, driver program, etc.

  3. Boot File: The boot file in the boot entry is the boot program of the operating system, responsible for loading the operating system. The boot file of Windows is bootmgfw.efi, and the boot file of Linux is vmlinuz.

On this basis, let’s take a look at how UEFI starts the operating system.

  1. Each boot loader corresponds to a .efi file, and this .efi file is the boot file of the boot loader, responsible for loading the boot loader. After UEFI completes the self-test, it reads all .efi files in the EFI partition. If you enter the BIOS settings at this time, you will see the boot entries in the EFI partition. These boot entries have a priority sequence, and their order can be adjusted in the BIOS settings.

    For example, the highest priority boot entry in the figure below is rEFInd, followed by Windows Boot Manager, and finally ubuntu. When the computer starts, it will first try to load rEFInd, if rEFInd does not exist, it will try to load Windows Boot Manager, and so on.

    UEFI Boot Entries

  2. If rEFInd is successfully loaded, rEFInd will read the refind.conf configuration file in the EFI partition, generate a boot menu according to the configuration file, and display it on the screen. Each menu item corresponds to a boot entry, and boot entries are generally divided into two types: operating system kernel images and boot loaders.

    • Operating System Kernel Image: Corresponds to the operating system’s kernel file, such as Linux’s vmlinuz file, Windows’s bootmgfw.efi file.
    • Boot Loader: Corresponds to the .efi file of the boot loader, such as Grub2’s grubx64.efi file.

    Boot Entries Loaded by rEFInd

  3. After the user selects a menu item, rEFInd will load the corresponding boot entry. If the boot entry is an operating system kernel image, rEFInd will directly load the operating system; if the boot entry is a boot loader, rEFInd will load the boot loader, and the boot loader will load the operating system.

  4. If the boot loader wants to start a Linux system, it will first load the Linux kernel file vmlinuz-xxx, then load the Linux initial file system file initrd-xxx.img or initramfs-xxx.img, and finally load the Linux system. These two files are in the /boot directory of the Linux system.

Boot Entry Configuration During Multi-System Installation

As mentioned above, the boot files of multiple systems are stored in the same EFI partition, so when installing multiple systems, each system will create a boot file in the EFI partition, so there will be multiple boot files, each boot file corresponds to a system. In this way, you can start different systems by selecting different boot files.

When installing multiple operating systems, we can put the boot files of each system in the same EFI partition, or put the boot files of each system in different EFI partitions. Both methods have their advantages and disadvantages, and the specific choice depends on personal preferences.

  1. Same EFI Partition

    In this case, the hard disk partition structure is as follows:

    Same EFI Partition

    Advantages: Easy to manage, only one EFI partition is needed, no need for multiple EFI partitions. Easier to configure boot loaders.

    Disadvantages: All boot files are in one EFI partition. If the EFI partition is damaged, all systems will not be able to start.

    The specific operation of installing multiple systems is as follows:

    1. Hard Disk Partition: Divide an EFI partition on the hard disk, with a size of at least 1GB, and format it as FAT32. Other partitions can be determined according to the requirements of each operating system, for example, Windows generally requires at least 52GB of space, and Linux generally requires at least 20GB of space.
    2. Install Windows: If you are installing multiple operating systems with both Windows and Linux, it is recommended to install Windows first. Because the boot program of Windows will overwrite the boot program of other previously installed operating systems, causing the previously installed Linux to fail to start. When installing Windows, select the partition for Windows, and Windows will automatically create a boot file in the EFI partition.
    3. Install Each Linux: For each Linux system, when installing, select custom partitioning, manually mount the EFI partition to /boot/efi, and mount the partition prepared for Linux to /, and create a swap partition and /home partition if necessary. After installation, Linux will create a boot file in the EFI partition.
    4. Configure Boot Loader: After installing multiple operating systems, we need to configure the boot loader so that we can select the operating system to start. These contents will be detailed later.

  2. Different EFI Partitions

    In this case, the hard disk partition structure is as follows:

    Different EFI Partitions

    Advantages: Each system has its own EFI partition, which does not interfere with each other. If the EFI partition of one system is damaged, other systems are not affected.

    Disadvantages: Multiple EFI partitions are needed, which are more cumbersome to manage. The boot files of each system are in different EFI partitions, making it difficult to configure boot loaders.

    The specific operation of installing multiple systems is as follows:

    1. Hard Disk Partition: Divide a space for each system on the hard disk. Do not create an EFI partition first, the EFI partition will be created in each system’s partition when installing the system.
    2. Install Windows: When installing Windows, select the partition for Windows, and Windows will automatically create an EFI partition in that partition.
    3. Install Linux: For each Linux system, when installing, select the partition for this system, create an EFI partition of about 200MB in this partition, mount point is /boot/efi; mount the remaining space as a partition prepared for Linux, mount point is /; create a swap partition and /home partition if necessary.
    4. Configure Boot Loader: After installing multiple operating systems, we need to configure the boot loader so that we can select the operating system to start. These contents will be detailed later.

Boot Directory Structure

Let’s take a look at the structure of the boot directory and what files are created when installing an operating system. Here, it is assumed that the boot files of multiple operating systems are placed in the same EFI partition. We have installed 3 operating systems: Windows, Ubuntu, and Arch Linux. Ubuntu uses Grub2 as the boot loader, and Arch Linux uses systemd-boot as the boot loader. We also installed rEFInd as the boot loader in the Ubuntu system.

  1. EFI Partition

    The EFI partition is a FAT32 formatted independent partition, generally with a size of about 1GB. The EFI partition mainly contains the boot files of various boot loaders.

    The directory structure of the EFI partition is as follows:

     1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19

    EFI
├── Boot
│   └── bootx64.efi
├── Microsoft
│   └── Boot
│       ├── BCD
│       ├── BCD.LOG
│       ├── BCD.LOG1
│       ├── BCD.LOG2
│       ├── bootmgfw.efi
│       ├── bootmgr.efi
│       └── boot.stl
├── systemd
│   └── systemd-bootx64.efi
└── ubuntu
    ├── grub.cfg
    ├── grubx64.efi
    ├── mmx64.efi
    └── shimx64.efi
    • EFI/Boot/bootx64.efi: The default boot file of UEFI, generally points to the boot file of Windows EFI/Microsoft/Boot/bootmgfw.efi.
    • EFI/Microsoft/Boot/bootmgfw.efi: The boot file of Windows, responsible for loading the Windows operating system.
    • EFI/systemd/systemd-bootx64.efi: The boot file of systemd-boot, responsible for loading the Linux operating system.
    • EFI/ubuntu/grubx64.efi: The boot file of Grub2, responsible for loading the Linux operating system.
    • EFI/ubuntu/shimx64.efi: The boot file of Secure Boot, used to load Grub2.
    • EFI/ubuntu/mmx64.efi: The boot file of Grub2, used to load Grub2.
    • EFI/ubuntu/grub.cfg: The configuration file of Grub2, containing the configuration of each boot entry.

  2. Install Operating System

    When installing Ubuntu, select custom partitioning, manually mount the EFI partition to /boot/efi, and mount the partition prepared for Linux to /. After installation, Ubuntu will create the EFI/ubuntu directory in the EFI partition, which contains the boot files and configuration files of Grub2. Ubuntu will create two files in the /boot directory: vmlinuz and initrd.img, these two files are the kernel file and initial file system file of Linux. The boot file of Grub2 will recognize these two files and create boot entries, select the corresponding boot entry at startup, and load the Ubuntu system.

    In the Ubuntu system, you can enter /boot/efi/EFI to view the directory structure of the EFI partition.

    1
2
3
4
5
6
7
8
9

    /boot
├── efi
│   └── EFI
│       ├── Boot
│       ├── Microsoft
│       ├── systemd
│       └── ubuntu
├── vmlinuz
└── initrd.img

    Note that although /boot/efi/EFI is under /boot, the files in /boot/efi/EFI are in the EFI partition, while the other files in /boot are in the partition of the Ubuntu system. The files vmlinuz and initrd.img in /boot cannot be accessed in other systems, but if other systems also mount the EFI partition, then other systems can also access the files in /boot/efi/EFI.

    If you continue to install more operating systems, the operating system will generally ask you to choose a boot loader, you can choose to use Grub2, systemd-boot, or other boot loaders. The configuration of the boot loader is introduced below.

Boot Loader

The boot loader (Boot Loader) is responsible for loading the operating system’s boot program, and each boot program is a boot entry (Boot Entry). Common boot loaders include Grub (Grub2), rEFInd, Clover, etc. Here we mainly introduce Grub2 and rEFInd.

Grub2

Grub2 (GNU GRand Unified Bootloader 2) is a commonly used boot loader on Linux systems, powerful, and supports multi-system boot. Grub2’s configuration file is /boot/grub/grub.cfg, generally generated by the grub-mkconfig command.

Grub2’s configuration file is relatively complex but powerful, and can customize various boot entries. Grub2’s theme can also be customized, but it is relatively complex.

Grub2 Configuration

  1. Configuration File

    Grub2’s main configuration file is /boot/grub/grub.cfg, which can be edited to configure Grub2’s boot entries.

    1

    sudo vim /boot/grub/grub.cfg

    However, it is generally not recommended to edit the grub.cfg file directly because this file is generated by the grub-mkconfig command. If you edit the grub.cfg file directly, it will be overwritten when updating Grub2 next time. It is recommended to configure Grub2 through the /etc/default/grub file and the configuration files in the /etc/grub.d/ directory.

  2. Boot Entry Configuration

    Grub2’s boot entry configuration is relatively complex, for example:

    1
2
3
4
5

    GRUB_DEFAULT=0
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX=""
    • GRUB_DEFAULT: The number of the default boot entry, starting from 0.
    • GRUB_TIMEOUT: The time the boot menu is displayed, in seconds.
    • GRUB_DISTRIBUTOR: The system’s distributor.
    • GRUB_CMDLINE_LINUX_DEFAULT: The default boot parameters of the Linux kernel.
    • GRUB_CMDLINE_LINUX: The boot parameters of the Linux kernel.

  3. Customize Theme

    Grub2’s theme can be customized, you can put the desired theme files in the /boot/grub/themes directory. The theme directory contains theme files, font files, background images, etc., and a configuration file named theme.txt that can configure various properties of the theme.

    You can specify the theme file in the configuration file /etc/default/grub:

    1

    GRUB_THEME="/boot/grub/themes/theme-name/theme.txt"

More Grub2 configurations can be found at Grub2 Configuration.

rEFInd

rEFInd is a UEFI-based boot loader, powerful, and supports multi-system boot. rEFInd’s configuration file is /boot/efi/EFI/refind/refind.conf, generally generated by the refind-install command.

rEFInd’s configuration file is relatively simple but powerful, and can customize various boot entries. rEFInd’s theme can also be customized, relatively simple.

rEFInd Installation

rEFInd installation is relatively simple, you can directly download the rEFInd installation package, unzip it to the EFI partition. You can also install rEFInd using the refind-install command.

1

refind-install

After installation, rEFInd will create the EFI/refind directory in the EFI partition, which contains rEFInd’s boot files and configuration files.

rEFInd Configuration

rEFInd’s configuration file is /boot/efi/EFI/refind/refind.conf, you can edit this file to configure rEFInd’s boot entries.

1

sudo vim /boot/efi/EFI/refind/refind.conf

  1. Boot Entry Configuration

    rEFInd’s boot entry configuration is relatively simple, for example:

    1
2
3

    timeout 5
hideui singleuser
scanfor manual,external
    • timeout: The time the boot menu is displayed, in seconds.
    • hideui: Hide the boot menu and only display single-user mode.
    • scanfor: The way to scan boot entries, you can scan manually configured boot entries, or scan boot entries on external devices.

  2. Customize Theme

    rEFInd’s theme can be customized, you can put the desired theme files in the /boot/efi/EFI/refind/theme directory. The theme file is a CSS file, you can modify the color, font, background, etc.

    You can specify the theme file in the configuration file /boot/efi/EFI/refind/refind.conf:

    1

    include themes/theme-name/theme.conf

  3. Hide Boot Entries

    Sometimes rEFInd will scan many unnecessary boot entries, for example, if you choose to use Grub2 as the boot loader when installing the system (Deepin, Fedora, etc. systems will install Grub2 by default, and it seems that you can’t cancel it during installation), then rEFInd will scan Grub2’s boot entries. You can hide these boot entries by configuring the file /boot/efi/EFI/refind/refind.conf. rEFInd can choose to ignore certain files (dont_scan_files), tools (dont_scan_tools), directories (dont_scan_dirs), and volumes (dont_scan_volumes).

    1
2

    dont_scan_files shim.efi,mmx64.efi
dont_scan_dirs ESP:/EFI/ubuntu,EFI/deepin,EFI/fedora

Troubleshooting

  1. Install System on SD Card or USB Drive

    • If your computer has an SD card slot, you can choose to install the system on the SD card.
    • Similar to the method of installing multiple operating systems mentioned above, there are two EFI partition methods for installing the system on the SD card, one is to create an EFI partition on the SD card, and the other is to mount the EFI partition on the hard disk to /boot/efi when installing the system.
    • For the /boot partition, you can choose to create it directly on the SD card, or you can create a 500M ext4 partition on the hard disk first, and then mount it to /boot when installing the system. The /boot partition mainly stores kernel files and boot files, generally about 200M of space is enough, but if you choose to back up multiple kernels, you will need more space. Fedora system will limit the /boot partition to no less than 512M.
    • If you choose to put the /boot partition on the SD card, you may encounter some security restrictions, for example, Secure Boot may prevent booting from the SD card. You need to register the registration key or disable Secure Boot.
    • I generally choose to put the EFI partition and /boot partition on the hard disk.

    I haven’t tried installing the system on a USB drive yet, but the principle should be the same as installing it on an SD card.

  2. Fedora Fails to Boot

    After installing Fedora on the SD card, I encountered a problem that the system could not boot. rEFInd can scan Fedora’s kernel files vmlinuz-xxx and initramfs-xxx.img, but it will hang halfway through the boot process, reporting:

    1
2
3
4
5
6
7

    Failed to switch root: Specified switch root path /sysroot does not seem to be an OS tree. os-release file is missing.
initrd-switch-root.service: Main process exited, code=exited, status=1/FAILURE
initrd-switch-root.service: Failed with result 'exit-code'.
Failed to start initrd-switch-root.service: Switch Root.
Startup finished in 1.073s (kernel) + 1.000s (initrd) + 1.000s (userspace) = 3.073s.
initrd-switch-root.service: Triggering OnFailure= dependencies.
Started emergency.service - Emergency Shell.

    After checking in the Emergency Shell, I found that the /sysroot directory was empty, with no files. Normally, the /sysroot directory should contain the files of the operating system after loading the kernel and initializing the file system.

    So this problem is because the SD card is not correctly mounted when starting the kernel and initializing the file system. You can manually mount the SD card in the Emergency Shell, then exit to exit the Emergency Shell, and the system can start normally.

    1
2

    mount /dev/sda1 /sysroot
exit

    However, this is obviously not a good solution because you need to manually mount the SD card every time you start it. So the correct solution is to let rEFInd correctly mount the SD card when starting the kernel, which requires adding a root parameter to the boot options. You can add a menu item with an options parameter in the rEFInd configuration file /boot/efi/EFI/refind/refind.conf.

    1
2
3
4
5
6

    menuentry "Fedora" {
    volume "SD-boot"
    loader /vmlinuz-xxx
    initrd /initramfs-xxx.img
    options "root=/dev/sda1"
}

    However, this solution is not very good because

    • After each kernel update, you need to manually modify the rEFInd configuration file.
    • If you have multiple kernels, this menu item cannot generate submenus automatically, you need to manually add menu items for each kernel.

    So a better solution is to let the entire boot partition use the root option. The correct way is to create a refind_linux.conf file in the root directory of the /boot partition, and then add a root parameter in the rEFInd configuration file /boot/efi/EFI/refind/refind.conf.

    1

    "Boot with standard options" "root=/dev/sda1"

    The problem is finally solved!

comments powered by Disqus