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Complete Method to Add systemd in Buildroot

Buildroot is a commonly used root filesystem build tool for embedded Linux, which defaults to using <span>busybox init</span> as the initialization system. The following is the process of adapting systemd for the BeagleBone Green (hereinafter referred to as BBG, which is part of my xboard project) development board.

• • Open-source hardware board BBG
• • U-Boot 2020.10
• • Kernel 5.15.173
• • Buildroot 2021.02
• • systemd 247.3

The main purpose of xboard is to give old boards a new look, that is, to update outdated ARM boards with the ARMv7 instruction architecture to run with a new kernel (5.15), while also studying the startup of popular development boards with ARMv8 instruction SoCs like RK3568/AM62x/iMX8M (mainly focusing on kernel 6.1). Currently, the ARMv7 part of this project is basically complete and will be released later.

1. Preliminary Preparation

• • Buildroot compilation environment installed (refer to the official Buildroot documentation: https://buildroot.org/downloads/manual/manual.html#requirement)
• • Configuration file for BBG compiled successfully ( <span>configs/xboard_bbg_defconfig</span>)

2. Step 1: Enable systemd through Buildroot Menu Configuration

1. Enter the Buildroot configuration interface

Execute the following command in the Buildroot root directory to open the graphical configuration menu (requires installation of <span>ncurses-dev</span> dependency:<span>sudo apt install libncurses5-dev</span>):

make O=bbg xboard_bbg_defconfig
make O=bbg menuconfig

O is a separate compilation directory for easier management

2. Select systemd as the initialization system

2.1 Switch the initialization system to systemd

Support for systemd is crucial

2.2 Configure the toolchain (systemd usually requires glibc)

systemd requires support from the glibc library

2.3 Enable optional features for systemd

Enter the systemd submenu to enable additional features, navigate to Target packages → System tools, enter systemd, find and enable the following configurations:

• • Key Note:<span>systemd</span> selected, Buildroot will automatically depend on components such as <span>dbus</span> and <span>libudev</span>, no need to enable them manually.
• 

Option Name	Main Function	Usage Scenario	Recommendation
Services for booting from initrd	Provides system services for initrd boot	Systems booting from initial RAM disk	Enable only when initrd boot is needed
install kernel-install and related files	Installs kernel installation tools and files	Systems requiring dynamic kernel installation and updates	Recommended to enable for easier kernel management
systemd-analyze	System boot performance analysis tool	Debugging boot time, service dependencies	Enable during development debugging, optional in production
enable journal remote tools	Remote log receiving and sending tools	Centralized log management, remote debugging	Enable when remote logging is needed
enable backlight support	Backlight control support	Laptops, embedded devices with displays	Enable for devices with backlight control
enable binfmt tool	Binary format registration support	Running executables of non-native architectures	Enable when running cross-architecture binaries
enable coredump hook	Core dump handling hook	Application crash debugging and analysis	Enable during development debugging
enable pstore support	Persistent storage support	Saving kernel crash logs and other diagnostic information	Recommended to enable for easier problem diagnosis
enable firstboot support	First boot initialization configuration	Factory settings for productized devices	Strongly recommended for productized devices
enable hibernation support	System hibernation support	Scenarios requiring saving system state to disk	Enable for devices with hibernation needs
enable hostname daemon	Hostname daemon	Dynamic hostname management	Recommended to enable
enable hwdb installation	Hardware database installation	Device identification and configuration	Recommended to enable
enable import daemon	System image import daemon	Container and virtual machine image management	Enable when containers/VMs are needed
enable locale daemon	Localization daemon	Multi-language support, keyboard layout management	Enable for internationalized devices
enable login daemon	Login daemon	User session and power management	Recommended to enable
enable machine daemon	Machine daemon	Container and virtual machine instance management	Enable when container functionality is needed
enable myhostname NSS plugin	Local hostname resolution plugin	Local hostname resolution service	Recommended to enable
enable network manager	Network manager	Network connection management and configuration	Enable when dynamic network management is needed
polkit support	Permission policy framework	Interaction between unprivileged and privileged processes	Enable when fine-grained permission control is needed
enable portable services	Portable services support	Containerized application deployment	Enable when portable services are needed
enable quotacheck tools	Disk quota check tools	Disk space management for multi-user systems	Enable for multi-user systems
enable random-seed support	Random seed support	Improving random number quality at boot	Recommended to enable for enhanced security
enable repart support	Partition adjustment support	Dynamic disk partition adjustment	Enable when automatic partition expansion is needed
enable resolve daemon	DNS resolution daemon	DNS resolution and caching service	Recommended to enable
enable rfkill tools	Wireless RF switch tools	Management of wireless devices like WiFi and Bluetooth	Enable for devices with wireless functionality
enable SMACK support	Simplified Mandatory Access Control	Enhancing system security	Enable for systems with high security requirements
enable sysusers support	System user management support	Dynamic creation of system users and groups	Recommended to enable for simplified user management
enable timedate daemon	Date and time daemon	System time and timezone management	Recommended to enable
enable timesync daemon	Time synchronization daemon	System time synchronization service	Recommended to enable
enable tmpfiles support	Temporary file management support	Creation and cleanup of temporary files and directories	Recommended to enable
enable userdb daemon	User database daemon	Dynamic user information query service	Enable when dynamic user management is needed
enable vconsole tool	Virtual console tool	Management of virtual terminal settings	Recommended to enable

2.4 Configure the filesystem image format

The format of the device filesystem, supporting the latest ext4 format

Step 3: Configure the Linux Kernel

Systemd has specific requirements for the kernel. We need to ensure that the kernel includes the necessary options. Use Buildroot’s kernel menu (recommended)

make O=bbg linux-menuconfig

In the pop-up Linux kernel configuration window, use the search function (press <span>/</span> key) to ensure the following options are enabled (<span>=y</span> or <span>=m</span>):

1. 1. Search for <span>CONFIG_CGROUPS</span>

• • Ensure <span>General setup -> Control Group support</span> is enabled.
• • In its submenu, typically need to enable <span>... -> Memory controller</span> and <span>... -> CPU controller</span>, etc.

2. Search for <span>CONFIG_AUTOFS4_FS</span>

• • Ensure <span>File systems -> Network File Systems -> Kernel automounter version 4 support (also supports v3)</span> is enabled.

3. Search for <span>CONFIG_TMPFS_POSIX_ACL</span>

• • Ensure <span>File systems -> Pseudo filesystems -> Tmpfs POSIX Access Control Lists</span> is enabled.

4. Search for <span>CONFIG_TMPFS_XATTR</span>

• • Ensure <span>File systems -> Pseudo filesystems -> Tmpfs extended attributes</span> is enabled.

Other potentially required options:

• • <span>CONFIG_DEVTMPFS</span> and <span>CONFIG_DEVTMPFS_MOUNT</span> (usually enabled by default, crucial for managing <span>/dev</span>)
• • <span>CONFIG_FANOTIFY</span> (for file monitoring)
• • <span>CONFIG_SECCOMP</span> (system call filtering)

Step 4: Clean and Compile

Since core system components (C library and Init) have been changed, it is recommended to perform a clean rebuild.

# Full clean (safest but time-consuming)
make clean

# Alternatively, if you do not want to fully clean, you can try to force rebuild systemd and related packages
# make systemd-dirclean
# make busybox-dirclean # because we want to replace it

# Start compilation
make

The compilation process will take a long time (from tens of minutes to several hours, depending on your network and computer performance).

Step 5: Prepare the SD Card and Test

After compilation is complete, the output files are in the <span>bbg/output/images/</span> directory.

1. 1. Insert the SD card into the computer, find the SD card device (usually <span>/dev/sdb</span>, be careful not to select the wrong disk!)
2. 2. Use the <span>dd</span> command to write the image (if <span>sdcard.img</span> is generated)

   sudo dd if=output/images/sdcard.img of=/dev/sdb bs=1M status=progress

3. 3. Or, prepare manually (if <span>zImage</span>, <span>*.dtb</span>, and <span>rootfs.tar</span> are generated):

• • Partition the SD card into two partitions: FAT32 (for boot) and EXT4 (for rootfs).
• • Copy the <span>zImage</span> and <span>*.dtb</span> files to the FAT32 partition.
• • Extract the <span>rootfs.tar</span> to the EXT4 partition.
• • Ensure <span>boot/cmdline.txt</span> or U-Boot environment variables correctly point to the new rootfs.

4. Boot BBG: Insert the SD card into BBG, connect the serial cable to view the boot log, press the user key and then power on.

Step 6: Verify systemd

After the system boots, log in via the serial port and execute the following commands to verify:

# 1. Check the current running init system
ps  
# 2. Check if systemctl is working
systemctl --version

Check logs via journalctl, there are many control items

# 3. Check logs (now managed by journald)
journalctl

Bonus

During the compilation process, due to the cross-compiler being too old and the kernel being too new, an error regarding ARPHRD_MCTP was reported.

To avoid changing the current cross-compiler and kernel versions, remove references to ARPHRD_MCTP from the systemd source code to compile successfully.

uildroot$ grep -rn "ARPHRD_MCTP" ./bbg/
./bbg/build/host-systemd-247.3/build/src/basic/arphrd-from-name.h:195:      {"MCTP", ARPHRD_MCTP},
./bbg/build/host-systemd-247.3/build/src/basic/arphrd-to-name.h:57:        case ARPHRD_MCTP: return "MCTP";
./bbg/build/host-systemd-247.3/build/src/basic/arphrd-from-name.gperf:64:MCTP, ARPHRD_MCTP

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