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16.2 Dual-Boot Installation (FreeBSD Installed Second)

This section uses FreeBSD-14.2-RELEASE-amd64-disc1.iso as an example to demonstrate installing FreeBSD as a dual-boot system on a UEFI device that already has Windows 11 24H2 pre-installed, with emphasis on ESP partition space and boot management.

Tip

The example in this section requires installing another operating system (such as Windows) first, then installing FreeBSD. Please follow this installation order.

Simple Installation Method

The following describes a relatively simple installation method.

Note

When installing FreeBSD using the method described in this section with ZFS, only the storage pool zroot (zpool) is created and directly mounted at /, without creating zroot/ROOT/default or other datasets. After installation, you can create datasets yourself and replace them; if you need the same initial layout as the automatic installation, please refer to the "Shell Partitioning" section of this chapter.

To install FreeBSD using the simple method, follow these steps.

First, you need to reserve space on the hard disk for FreeBSD. In a typical Windows installation, the last partition (in this example, nda0p4) is usually a recovery partition, which is not suitable for installing a system. The space reserved for FreeBSD does not need to be at the end of the hard disk; a middle position also works.

After partitioning, check the disk partition layout in FreeBSD, with the following results:

# gpart show
=>       34  419430333  nda0  GPT  (200G)
         34       2014        - free -  (1.0M)
       2048     204800     1  efi  (100M) # EFI partition
     206848      32768     2  ms-reserved  (16M) # MSR partition
     239616  207992832     3  ms-basic-data  (99G) # C drive (NTFS data partition), approximately 100G space reserved for FreeBSD
  417947648    1478656     4  ms-recovery  (722M) # Recovery partition
  419426304       4063        - free -  (100G)

You should disable Secure Boot and Fast Startup. Secure Boot prevents unsigned boot loaders from running, and FreeBSD's boot loader is not currently signed by Microsoft, so Secure Boot must be disabled. Fast Startup puts Windows into a special hibernation state when shutting down, which prevents other systems from properly accessing NTFS partitions. You can also use Windows Settings → System → Recovery → Advanced Startup to select booting from a USB device, then boot the FreeBSD installer normally until you reach the partition selection interface.

Partition selection interface

Select Manual here.

Tip

The partition editor interface used here is actually the same as the software sade (sysadmins disk editor, system administrator disk editor), and they share the same codebase. The diskmgmt module in bsdconfig directly calls sade.

Here you can view the hard disk partition layout. The image shows a single hard disk with a 300 MB EFI system partition, a 16 MB MSR partition, a 64 GB Windows system partition (i.e., C drive), and unshown free space. Select Create directly.

Hard disk partition layout

Here, enter the partition type on the first line (i.e., the Filesystem type listed below). If you need to add a swap partition, add it first in this step, because partitions are allocated from the beginning or end of the free space, and adding it later makes it difficult to control the partition size. Adding swap first allows better control of its position. When adding a UFS or ZFS partition, enter / in the Mountpoint field to mount this partition to the root directory. Label is FreeBSD's volume label (gptlabel) used to identify the partition; you can fill it in or leave it blank as needed. Here, ZFS is used without adding a swap partition, and the volume label zroot is entered.

Creating a partition

Use the Tab key to move the focus to OK, then press Enter to confirm.

Confirming partition creation

A warning will appear that the ZFS partition may not be bootable, but actual testing shows it can boot normally. This warning is a generic message from the installer and does not apply to UEFI configurations. Select Yes to dismiss this warning:

ZFS partition warning

Note

Set the mount point of the 300 MB EFI system partition created by Windows to /boot/efi, so that FreeBSD can correctly find and use the existing EFI partition, avoiding the confusion of creating multiple EFI partitions.

Select Finish

Finishing partition setup

Select Commit

Committing partition changes

After this, the normal installation process will proceed. After installation is complete, list all ZFS pools and their status in the system:

After entering the system, you can see there is only one root dataset. You can manually adjust the datasets to match the automatic installation layout, or refer to the Shell partitioning section below to partition during installation.

Shell Partitioning

At this point, still on the partition selection interface, select Shell:

Selecting Shell partitioning

You will then enter the terminal (TTY):

Shell terminal interface

Execute the following commands.

Loading the ZFS Kernel Module

ZFS support is not built into the kernel but is provided as a loadable module.

The default installation image may not have ZFS enabled, so you also need to load the ZFS kernel module:

You can verify the module is loaded successfully via kldstat.

Configuring ZFS Alignment (Only Affects Newly Created Disk Partitions)

Force the ZFS file system to use 4K alignment, which better adapts to the physical sector size of modern hard disks and improves read/write performance:

Tip

The parameter 12 represents a sector size of 2^12 = 4096 bytes (4 KB). The default parameter (which can be viewed with the command sysctl vfs.zfs.vdev.min_auto_ashift) is 9, meaning 2^9 = 512 bytes, which is the sector size of traditional hard disks.

Thought Exercise

When using NVMe hard disks, the default parameter for a new installation (UEFI+GPT, no freebsd-boot partition) is typically 12. But what exactly does 4K alignment align to? SSDs do not have the concept of physical sectors like traditional mechanical hard disks.

Creating a Swap Partition

Create a 4 GB, 4K-aligned FreeBSD swap partition on the nda0 disk and label it as swap:

Option descriptions:

Option
Description

-t

Specify partition type

-l

Specify volume label

-s

Specify partition size

-a

Specify alignment (e.g., 4k)

Please replace nda0 with the actual hard disk identifier as appropriate.

Creating a ZFS Partition

Create a 4K-aligned FreeBSD ZFS partition on the nda0 disk and label it as zroot:

The above setting will use all remaining free space. Please replace nda0 with the actual hard disk identifier.

Viewing Partition Layout

Display the system disk partition layout:

Mounting a Temporary File System to Prepare for Installation

Mount a temporary file system (tmpfs) so that files needed during the installation process can be temporarily stored in memory, avoiding frequent disk writes:

Creating a ZFS Pool

Create the ZFS pool zroot:

This command sets the mount point of the zroot pool to /mnt, enables LZ4 compression to save space and improve read/write performance, and disables access time recording to reduce disk writes.

Option descriptions are as follows:

Option
Description

-o altroot=/mnt

Temporarily mount it at /mnt

-O compress=lz4

Enable lz4 compression (can be changed to zstd, etc.)

-O atime=off

Disable access time recording

-m none

Do not set a mount point

/dev/gpt/zroot

The partition just created

You can verify the pool's health status via zpool status zroot.

Creating ZFS Datasets

The following dataset settings are created with reference to usr.sbin/bsdinstall/scripts/zfsboot in the FreeBSD source code. FreeBSD itself continues to evolve, and ZFS datasets may differ between versions. If readers want to create the same dataset structure as the default installation, they should refer to the usr.sbin/bsdinstall/scripts/zfsboot file of the corresponding branch.

  • Create the root dataset

This creates the dataset zroot/ROOT without setting a mount point (mountpoint=none).

Such datasets without a specific mount point typically serve as containers for the system root dataset, under which sub-datasets for actual mounting or exclusion purposes will be created.

  • Create the default root dataset

This creates the dataset zroot/ROOT/default and mounts it at the root directory /. This dataset will serve as the system's default root file system.

  • Create the /home dataset

This creates the dataset zroot/home and mounts it at /home, typically used for storing user home directories.

  • Create the /tmp dataset

This creates the dataset zroot/tmp and mounts it at /tmp, allowing file execution (exec=on) but disabling setuid (setuid=off) to prevent files in this directory from using setuid to escalate privileges.

  • Create the zroot/usr dataset

This creates the zroot/usr dataset with canmount=off, which prevents automatic mounting. This allows related sub-datasets to be organized together without this parent dataset being mounted separately.

  • Create the /usr/ports dataset

This creates the /usr/ports dataset with setuid disabled (setuid=off).

  • Create the /usr/src dataset

This creates the /usr/src dataset.

  • Create the /var dataset

This creates the /var dataset with canmount=off, meaning it will not be automatically mounted.

  • Create the /var/audit dataset

This creates the /var/audit dataset with execution disabled (exec=off) and setuid disabled (setuid=off).

  • Create the /var/crash dataset

This creates the /var/crash dataset with execution disabled (exec=off) and setuid disabled (setuid=off).

  • Create the /var/log dataset

This creates the /var/log dataset with execution disabled (exec=off) and setuid disabled (setuid=off).

  • Create the /var/tmp dataset

This creates the /var/tmp dataset with setuid disabled (setuid=off).

  • Create the /var/mail dataset

This creates the zroot/var/mail dataset with access time recording enabled (atime=on), typically used for storing mail data because mail programs may need to know the last access time of files.

Tip

The above parameters are referenced from the default configuration of bsdinstall(8). After installation, you can also view related properties with the command zfs get exec,setuid,mountpoint. The specific code is located at usr.sbin/bsdinstall/scripts/zfsboot.

Related file structure:

Modifying Directory Permissions

Set the permissions of /mnt/tmp and /mnt/var/tmp to 1777 (sticky bit) to ensure correct temporary directory permissions, allowing any user to create files in these directories but only delete files they created:

Configuring the Swap Partition in fstab

Add the swap partition /dev/nda0p5 to the temporary fstab file so that the system can automatically mount this swap partition at boot:

Note: replace /dev/nda0p5 with the actual swap partition device name, which can be confirmed using the gpart show nda0 command.

Tip

\t is the escape character for a tab (i.e., the character corresponding to the Tab key), used for aligning fields. Using spaces can achieve the same effect. You can also use the ee /tmp/bsdinstall_etc/fstab command to manually edit this file and write a line in the following format:

The same applies below.

Setting Up Boot Entries and UEFI

  • Set the boot file system (bootfs) of the ZFS pool to zroot/ROOT/default, so the system will automatically boot from this dataset at startup:

  • Require the system to enable the ZFS service at boot.

\n represents the newline character in Unix/Linux systems.

Windows text files typically use \r\n (carriage return + line feed) for line endings.

This command has the same effect as using ee /tmp/bsdinstall_etc/rc.conf to edit the file and add the line zfs_enable="YES".

  • Mount the existing EFI system partition so that FreeBSD boot files can be added to it:

Note: replace /dev/nda0p1 with the actual EFI partition device name.

  • Create a boot directory for FreeBSD in the EFI system partition

  • Copy the FreeBSD EFI boot file to the boot directory

  • Use the efibootmgr tool to add a boot entry named FreeBSD to the motherboard UEFI firmware. After adding, the FreeBSD option will appear in the UEFI boot menu at startup.

  • Unmount the EFI system partition

Directory structure:

  • Exit the Shell

The installer will automatically continue with the remaining process.

Completion

At this point, a set of ZFS dataset structure essentially the same as the automatic installer has been manually created (the automatic installation typically also creates a separate /home/username dataset, which is not included here).

Display the ZFS file system status of the installed system:

References

Previous16.1 Dual-Boot Installation (FreeBSD Installed First)Next16.3 Installing FreeBSD on Tencent Cloud Lighthouse (Legacy Boot/MBR)

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