.. _beagleplay-understanding-boot: Understanding Boot ################## There are several phases to BeaglePlay boot. The simplest place to take control of the system is using :ref:`play-distro-boot`. It is simplest because it is very generic, not at all specific to BeaglePlay or AM62, and was included in the earliest BeagleBoard.org Debian images shipping pre-installed in the on-board flash. .. _play-distro-boot: Distro Boot *********** For some background on distro boot, see `the u-boot documentation on distro boot `_. There is also `BeaglePlay specific u-boot documentation `_. In :ref:`play-typical-extlinux-conf`, you can see line 1 provides a label and subsequent indented lines provide parameters for that boot option. .. _play-typical-extlinux-conf: .. code-block:: :caption: Typical /boot/firmware/extlinux/extlinux.conf file :linenos: label Linux eMMC kernel /Image append root=/dev/mmcblk0p2 ro rootfstype=ext4 rootwait net.ifnames=0 quiet fdtdir / #fdtoverlays /overlays/.dtbo initrd /initrd.img It is important to note that this file is not on the root file system of BeaglePlay. It is sitting on a separate FAT32 partition that is mounted at ``/boot/firmware``. You can see the mounted file systems and their formats in :ref:`play-boot-mounted-fs`. The FAT32 partition in this setup is often referred to as the boot file system. .. _play-boot-mounted-fs: .. code-block:: shell-session :caption: List of mounted file systems debian@BeaglePlay:~$ df Filesystem 1K-blocks Used Available Use% Mounted on udev 903276 0 903276 0% /dev tmpfs 197324 1524 195800 1% /run /dev/mmcblk0p2 14833640 12144024 1914296 87% / tmpfs 986608 0 986608 0% /dev/shm tmpfs 5120 4 5116 1% /run/lock /dev/mmcblk0p1 130798 53214 77584 41% /boot/firmware tmpfs 197320 32 197288 1% /run/user/1000 debian@BeaglePlay:~$ lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT mmcblk0 179:0 0 14.6G 0 disk ├─mmcblk0p1 179:1 0 128M 0 part /boot/firmware └─mmcblk0p2 179:2 0 14.5G 0 part / mmcblk0boot0 179:256 0 4M 1 disk mmcblk0boot1 179:512 0 4M 1 disk debian@BeaglePlay:~$ sudo sfdisk -l /dev/mmcblk0 Disk /dev/mmcblk0: 14.6 GiB, 15678308352 bytes, 30621696 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: dos Disk identifier: 0xba67172a Device Boot Start End Sectors Size Id Type /dev/mmcblk0p1 * 2048 264191 262144 128M c W95 FAT32 (LBA) /dev/mmcblk0p2 264192 30621695 30357504 14.5G 83 Linux To better understand BeaglePlay's U-Boot Distro Boot, let's install a Linux kernel and initramfs from the `Buildroot project `_. There is a pre-built image release at https://git.beagleboard.org/beagleboard/buildroot/-/releases/2023.11-beagle1. Currently, the Linux kernel image needs to be uncompressed and stored in the FAT32 file system. An initramfs image is a simple way to provide a starting root file system. When running Linux, some kind of root file system is required. An initramfs image is utilized on Debian systems to make sure any kernel modules needed are available and to provide a bit of a recovery opportunity in case the root file system is corrupted. You can learn more about initramfs and initrd on `the Debian Initrd Wiki page ` and `the Linux kernel documentation admin guide initrd entry `. In the case of utilizing Buildroot, the entire `Linux distribution `_ is incorporated into the initramfs root file system image. The contents of the initrd can be read using ``lsinitramfs /boot/firmware/initrd.img``. .. _play-copy-kernel: .. code-block:: shell-session :caption: Copy kernel to FAT32 filesystem debian@BeaglePlay:~$ wget https://git.beagleboard.org/beagleboard/buildroot/-/jobs/19194/artifacts/raw/public/beagleplay/images/Image --2023-12-19 22:17:54-- https://git.beagleboard.org/beagleboard/buildroot/-/jobs/19194/artifacts/raw/public/beagleplay/images/Image Resolving git.beagleboard.org (git.beagleboard.org)... 44.226.162.25 Connecting to git.beagleboard.org (git.beagleboard.org)|44.226.162.25|:443... connected. HTTP request sent, awaiting response... 200 OK Length: 32172544 (31M) [application/octet-stream] Saving to: ‘Image’ Image 100%[===================>] 30.68M 1.78MB/s in 18s 2023-12-19 22:18:13 (1.74 MB/s) - ‘Image’ saved [32172544/32172544] debian@BeaglePlay:~$ sudo cp Image /boot/firmware/Image-buildroot [sudo] password for debian: debian@BeaglePlay:~$ wget https://git.beagleboard.org/beagleboard/buildroot/-/jobs/19194/artifacts/raw/public/beagleplay/images/rootfs.cpio.gz --2023-12-19 22:16:44-- https://git.beagleboard.org/beagleboard/buildroot/-/jobs/19194/artifacts/raw/public/beagleplay/images/rootfs.cpio.gz Resolving git.beagleboard.org (git.beagleboard.org)... 44.226.162.25 Connecting to git.beagleboard.org (git.beagleboard.org)|44.226.162.25|:443... connected. HTTP request sent, awaiting response... 200 OK Length: 30111086 (29M) [application/octet-stream] Saving to: ‘rootfs.cpio.gz’ rootfs.cpio.gz 100%[===================>] 28.72M 21.5MB/s in 1.3s 2023-12-19 22:16:46 (21.5 MB/s) - ‘rootfs.cpio.gz’ saved [30111086/30111086] debian@BeaglePlay:~$ sudo cp rootfs.cpio.gz /boot/firmware/rootfs.cpio.gz-buildroot .. _play-modified-extlinux-conf: .. code-block:: :caption: Modified /boot/firmware/extlinux/extlinux.conf file :linenos: menu title Select image to boot timeout 10 default Buildroot label Debian kernel /Image append root=/dev/mmcblk0p2 ro rootfstype=ext4 rootwait net.ifnames=0 quiet fdtdir / #fdtoverlays /overlays/.dtbo initrd /initrd.img label Buildroot kernel /Image-buildroot append rootwait net.ifnames=0 quiet fdtdir / initrd /rootfs.cpio.gz-buildroot .. _play-boot-modified-kernel: .. code-block:: shell-session :caption: Reboot into modified kernel and rootfs debian@BeaglePlay:~$ sudo shutdown -r now Connection to 192.168.0.117 closed by remote host. Connection to 192.168.0.117 closed. jkridner@slotcar:~$ sudo nmap -n -p 22 192.168.0.0/24 Starting Nmap 7.94SVN ( https://nmap.org ) at 2023-12-19 17:32 EST ... PORT STATE SERVICE 22/tcp open ssh MAC Address: 50:3E:AA:AD:78:06 (TP-Link Technologies) Nmap scan report for 192.168.0.112 Host is up (0.00020s latency). ... jkridner@slotcar:~$ ssh root@192.168.0.112 The authenticity of host '192.168.0.112 (192.168.0.112)' can't be established. ED25519 key fingerprint is SHA256:EZdvLkCNMyhy4RhvseUSC5EwaJR5Kgpk8JZG9kF+pmk. This key is not known by any other names. Are you sure you want to continue connecting (yes/no/[fingerprint])? yes Warning: Permanently added '192.168.0.112' (ED25519) to the list of known hosts. root@192.168.0.112's password: # uname -a Linux BeaglePlay 6.6.3 #1 SMP Tue Dec 19 21:32:06 UTC 2023 aarch64 GNU/Linux # cat /etc/os-release NAME=Buildroot VERSION=2023.11-beagle1 ID=buildroot VERSION_ID=2023.11 PRETTY_NAME="Buildroot 2023.11" Booting U-Boot ************** .. _play-boot-install-emmc: .. literalinclude:: boot/install-emmc.sh :caption: Install bootloader to eMMC :language: bash :download:`install-emmc.sh `