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For the complete documentation index, see llms.txt. This page is also available as Markdown.

15.3 Boot Managers and UEFI Firmware

The Unified Extensible Firmware Interface (UEFI) is a modern computer firmware interface standard designed to replace the traditional Basic Input/Output System (BIOS).

The UEFI specification defines the interface between the operating system and platform firmware, providing Boot Services and Runtime Services, as well as non-volatile storage for boot variables.

FreeBSD supports both the traditional MBR standard and GUID Partition Table (GPT) boot methods. GPT partitions typically appear on computers using UEFI firmware, but FreeBSD can also boot from GPT partitions on machines with only traditional BIOS through gptboot(8).

The UEFI boot process differs architecturally from the traditional BIOS boot process.

In traditional BIOS systems, the firmware reads and executes the boot code from the Master Boot Record (MBR).

In UEFI systems, the firmware directly loads an EFI application from the FAT32 file system on the EFI System Partition (ESP). ESP is a dedicated partition with partition type GUID C12A7328-F81F-11D2-BA4B-00A0C93EC93B, typically mounted at /boot/efi. The UEFI boot loader is loader.efi. It can be loaded in two ways: directly by the firmware when configured through efibootmgr(8) or placed as the default boot program; when loader.efi resides within a UFS or ZFS file system, the firmware first loads boot1.efi, which then loads loader.efi. For systems installed with bsdinstall(8), loader.efi is loaded directly by the firmware.

UEFI System Detection Method

efibootmgr is a tool in the FreeBSD base system for viewing and managing EFI boot entries, interacting with UEFI firmware to manipulate boot entry configuration.

Running efibootmgr in a non-UEFI environment will produce the error efi variables not supported on this system.

# efibootmgr
efibootmgr: efi variables not supported on this system. root? kldload efirt?

If the current system is UEFI, efibootmgr will output something like the following:

# efibootmgr
Boot to FW : false
BootCurrent: 0004
BootOrder  : 0004, 0000, 0001, 0002, 0003
+Boot0004* FreeBSD
Boot0000* EFI VMware Virtual SCSI Hard Drive (0.0)
Boot0001* EFI VMware Virtual IDE CDROM Drive (IDE 1:0)
Boot0002* EFI Network
Boot0003* EFI Internal Shell (Unsupported option)

UEFI and efibootmgr

  • View current boot entries:

Tip

Use efibootmgr -v to view detailed information.

Set rEFInd to boot with priority (this does not set it as the default boot entry, but only changes the boot order in BIOS/UEFI):

Set the EFI boot order to 0000, 0001, 0002, 0003:

Warning

You should not use efibootmgr -o 0000 to directly specify the boot order, as this would set BootOrder to contain only 0000, causing other boot entries to be excluded from the boot order (the boot entries themselves still exist, but will not be attempted by the firmware for booting).

UEFI Operation Example

In multi-disk systems, it is sometimes necessary to merge scattered EFI partitions into a single partition for management to simplify boot configuration. The following example demonstrates how to unify EFI configuration files from two disks into one disk's EFI partition.

The directory structure of the EFI partition is as follows:

This example removes the EFI partition generated by the FreeBSD installation on nda0 and migrates FreeBSD's boot files to the EFI partition on the ada0 disk.

First disable Windows fast startup with the command powercfg /h off (if you can enter the BIOS setup interface, this is not necessary).

Then shut down and reboot into the FreeBSD system, creating a mount point:

Check whether ada0p1 (the first partition on the disk) is the EFI partition to be mounted by entering the command:

If the above command outputs ntfs, it means the partition is not an EFI partition;

Then check the second partition:

Output msdosfs indicates this is the EFI partition on the Windows disk.

Next, mount the EFI partition on the ada0 disk to FreeBSD's /mnt/efi:

Create a directory for the FreeBSD boot entry under the EFI path:

Copy the FreeBSD boot files to this path:

Create an EFI boot entry "FreeBSD 15.0" pointing to FreeBSD's boot program:

Reboot into Windows and use EasyUEFI to activate the FreeBSD 15.0 boot entry.

After confirming FreeBSD can boot normally, you can use DiskGenius or other partition tools to delete the EFI partition and its files on the nda0 disk.

Grub

Testing shows that in UEFI + ZFS environments, GRUB has compatibility issues when directly booting the FreeBSD kernel; it is generally recommended to use the chainload mechanism (such as configuring chainloader +1) for indirect booting. In traditional BIOS boot + UFS root file system environments, GRUB can directly boot the FreeBSD kernel using the kfreebsd command.

Troubleshooting

Current configuration errors (grub2-efi FreeBSD 15.0):

Adding the -vvv parameter shows detailed error information; the output is lengthy and can be viewed at https://gist.github.com/ykla/9b6de6c8d4eee524840acb9981bf850a.

rEFInd Boot Manager (Multi-System Boot Management)

In a multi-system environment, frequently entering the BIOS firmware interface to switch operating systems is inconvenient. You can use rEFInd to achieve a visual boot menu effect similar to Clover, allowing intuitive selection of the operating system to enter at boot time.

rEFInd is derived from rEFIt; its name can be understood as a combination of "re-find" (meaning "rediscover") and "EFI" (Extensible Firmware Interface), primarily used for managing UEFI boot, providing a graphical interface and flexible configuration options.

First, you need to download the rEFInd software. Open the download page Getting rEFInd from Sourceforge and click the A binary zip file link to start downloading. The version used when writing this section is refind-bin-0.14.2.zip.

Of the downloaded archive, only some files are required boot files. You only need to keep the refind folder; the remaining files are not needed.

Within the refind folder, only some boot files are needed. All files containing aa64 or ia32 in their names can be deleted (typically only the x64 version is kept).

The final files to keep are shown in the figure below.

rEFInd File Structure

Copy the refind.conf-sample file and rename it to refind.conf.

Typically, no manual configuration is needed. However, if existing operating systems cannot be automatically detected, manually add boot entries as follows:

Open the refind.conf file and add the following configuration in any blank area:

Directory structure:

Use DiskGenius to copy the processed refind folder to the EFI directory on the EFI System Partition (ESP).

Copy rEFInd to EFI Partition

Adding a Boot Entry

Use DiskGenius to add a UEFI boot entry.

Add UEFI Boot Entry

Click "Tools" in the menu bar and select "Set UEFI BIOS Boot Entry".

Set UEFI BIOS Boot Entry

In the new window, click "Add", then browse and select the refind_x64.efi file within the refind folder.

Select rEFInd Boot File

Move this boot entry to the top of the list to set it as the first boot entry. Save the settings and restart the computer to test.

Move Boot Entry to Top
rEFInd Boot Interface

After restarting, select any operating system option in the rEFInd interface to enter the corresponding system.

Appendix: rEFInd Themes

rEFInd supports various graphical themes.

This example uses the Matrix-rEFInd theme (inspired by the movie "The Matrix") for illustration.

The project address is: Matrix-rEFInd

Download the project archive Matrix-rEFInd-master.zip and extract it. Rename the extracted folder Matrix-rEFInd-master to Matrix-rEFInd.

Create a new local directory themes and place the renamed Matrix-rEFInd folder into it.

Copy this entire themes directory to the *EFI\refind* directory on the EFI System Partition.

Edit the refind.conf file (if you cannot edit directly on the ESP, copy it to the desktop, modify it, and overwrite the original file), adding the following line at the end of the file:

This will invoke the Matrix-rEFInd theme.

Observe the effect after reboot:

rEFInd Matrix Theme

Tip

If operating in a virtual machine (such as VMware, VirtualBox), due to the screen resolution limitations of their UEFI firmware, the rEFInd interface may not be able to display all operating system options simultaneously; you need to use arrow keys to switch views, which may differ from the effect shown in the figure above.

References

Exercises

  1. Test the multi-stage FreeBSD boot process under UEFI firmware in QEMU, verifying each stage of the EFI loader, loader.efi, and kernel loading.

  2. Attempt to compile the Clover boot manager on FreeBSD, documenting platform adaptation issues encountered during the compilation process.

  3. When installing FreeBSD, create separate EFI and freebsd-boot partitions, and compare the differences in system boot logs between the two boot methods.

Previous15.2 Boot Messages (dmesg)Next15.4 Processes and Daemons

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