Raspberry Pi: Difference between revisions

Revision as of 10:30, 26 September 2024

Warning: 11 Feb 2021 - There is currently a known bug upstream
kernel/initramfs cannot be loaded from subdirectory with same name as volume label. Since the kernel is installed to boot/, you must not use a label named boot for the fat32 partition.

This tutorial explains how to install Alpine Linux on a Raspberry Pi. Alpine Linux will be installed in diskless mode, hence, Alpine Local Backup (lbu) is required to save modifications between reboots.

For scenarios where there is not expected to be significant changes to disk after setup (like running a static HTTP server), this is likely preferable, as running the entire system from memory will improve performance (by avoiding the slow SD card) and improve the SD card life (by reducing the writes to the card, as all logging will happen in RAM). Diskless installations still allow you to install packages, save local files, and tune the system to your needs.

If any of the following apply, then installation in sys-mode installation is likely more appropriate.

There will be constant changes to the disk after initial setup (for example, if you expect people to login and save files to their home directories)
Logs should persists across reboots
Plan to install packages which consume more space than can be loaded into RAM
Plan to install kernel modules (such as ZFS)

Compability list

As of Alpine 3.19:

armhf (defconfig bcmrpi) - Raspberry Pi 1, Zero, ZeroW, cm1
armv7 (defconfig bcm2709) - Raspberry Pi 2, 3, 3+, Zero2W, cm3, cm3+
aarch64 (defconfig bcm2711) - Raspberry Pi 3, 3+, 4, 400, Zero2W, cm3, cm3+, cm4, 5

Preparation

Download the Alpine for Raspberry Pi tarball. Use the compability list above when choosing image/file to download.
Create a bootable FAT32 partition on your SD card. The partitioning and formatting part of the instructions on the linked page could be done using a graphical partitioning tool such as gnome-disks, just make sure the partition type is W95 FAT32 (LBA). (The current type can be found in the "Type" column in the output of fdisk -l.)
Extract the tarball to the root of the bootable FAT32 partition.

To setup a headless system, a bootstrapping configuration overlay file headless.apkovl.tar.gz may be added to enable basic networking, so that following configuration steps can be performed under ssh. Pi Zero may be configured with simple USB ethernet-gadget networking with another computer sharing its internet connection.

It is recommended to create a usercfg.txt file on boot partition to configure low-level system settings, as config.txt may be replaced during bootloader/system upgrades: details can be found here.
However, note some settings can only be set in config.txt, and will have no effect when specified in usercfg.txt (e.g. gpu_mem). Some interesting values include:

To enable the UART console: enable_uart=1
To enable audio: dtparam=audio=on
By default system will use legacy video driver: some options may be used to adjust displays modes (e.g. if you see black edges around your screen after booting the Pi, you can add disable_overscan=1). Alternatively Linux DRM-KMS driver may be used (see below).
If you plan to install on a Pi Compute Module 4 with I/O board, you may need to add: otg_mode=1

Recent versions include Broadcom firmware files. If you're using an older Alpine version, see section below.

Installation

Follow these steps to install Alpine Linux in Diskless Mode:

Insert the SD card into the Raspberry Pi and power it on
Login into the Alpine system as root. Leave the password empty.
Type setup-alpine
Once the installation is complete, commit the changes by typing lbu commit -d

Type reboot to verify that the installation was indeed successful.

Post Installation

Update the System

After installation, make sure your system is up-to-date:

apk update apk upgrade

Don't forget to save the changes:

lbu commit -d

Note: this does not upgrade the kernel. In order to upgrade the kernel, a full upgrade of the Alpine Linux version must be performed as described in upgrading Alpine Linux for removable media.

Linux Kernel Graphics Modes

By default system configuration will use legacy video driver: this driver has some limitations and is lacking support.
It is recommended to enable Linux DRM-KMS driver by adding the following to usercfg.txt:

# Enable DRM VC4 V3D driver
dtoverlay=vc4-kms-v3d
max_framebuffers=2

# Don't have the firmware create an initial video= setting in cmdline.txt.
# Use the kernel's default instead.
disable_fw_kms_setup=1

Note: This overlay disables legacy video options.

Install the Mesa drivers (Pi4 and Pi5):

apk add mesa-dri-gallium

Then reboot:

lbu_commit -d; reboot

Wireless drivers

As of Alpine 3.17, Wifi and Bluetooth drivers are available within install image: they are part of linux-firmware-brcm (and linked dependencies).
Since kernel 6.1.25 (i.e. Alpine 3.18), onboard bluetooth is enabled & autoprobed by default (it may be disabled by setting krnbt off).

Troubleshooting

raspinfo utility can be used as a first step to diagnose issues: it will make a log report of essential Pi system configuration, and is often used as a reference to submit questions or bug reports within Raspberry Pi community (Forums, Github, etc).
It can be installed with raspberrypi-utils-raspinfo subpackage.

Long boot time when running headless

If no peripherals are connected, the system might hang for an exceptionally long period of time while it attempts to accumulate entropy.

If this is the case, simply plugging in any USB device should work around this issue, since it increases the amount of entropy available to the kernel via interrupts.

apk indicating 'No space left on device'

Note some models of the Raspberry Pi such as the 3A+ only have 512M of RAM, which on fresh Alpine deployment will only leave around 200M for tmpfs root. It's important to keep this limitation in mind when using these boards.

Clock-related error messages

During the booting time, you might notice errors related to the hardware clock. Many Raspberry Pi does not have a hardware clock, thus you need to disable the hwclock daemon and enable swclock:

rc-update add swclock boot # enable the software clock rc-update del hwclock boot # disable the hardware clock

Persistent storage

Traditional disk-based (sys) installation

This material is proposed for merging ...

It should be merged with Classic install or sys mode on Raspberry Pi. There's an existing page for sys-installations on RasPi. (Discuss)

It is also possible to switch to a fully disk-based installation. This is not yet formally supported, but can be done somewhat manually. This frees all the memory otherwise needed for the root filesystem, allowing more installed packages.

Split your SD card into two partitions: the FAT32 boot partition described above (in this example it'll be mmcblk0p1) , and a second partition to hold the root filesystem (here it'll be mmcblk0p2). Boot and configure your diskless system as above, then create a root filesystem:

apk add e2fsprogs mkfs.ext4 /dev/mmcblk0p2

Now do a disk install via a mountpoint. The setup-disk script will give some errors about syslinux/extlinux, but you can ignore them. The Raspberry Pi doesn't need them to boot.

mkdir /stage mount /dev/mmcblk0p2 /stage setup-disk -o /media/mmcblk0p1/MYHOSTNAME.apkovl.tar.gz /stage # (ignore errors about syslinux/extlinux)

Add a line to /stage/etc/fstab to mount the Pi's boot partition again:

/dev/mmcblk0p1 /media/mmcblk0p1 vfat defaults 0 0

Now add a root=/dev/mmcblk0p2 parameter to the Pi's boot command line, either cmdline-rpi2.txt or cmdline-rpi.txt depending on model:

mount -o remount,rw /media/mmcblk0p1 sed -i '$ s/$/ root=\/dev\/mmcblk0p2/' /media/mmcblk0p1/cmdline-rpi2.txt

You might also consider overlaytmpfs=yes here, which will cause the underlying SD card root filesystem to be mounted read-only, with an overlayed tmpfs for modifications which will be discarded at shutdown.

N.B. the contents of /boot will be ignored when the Pi boots. It will use the kernel, initramfs, and modloop images from the FAT32 boot partition. To update the kernel, initfs or modules, you will need to manually (generate and) copy these to the boot partition or you could use bind mount, in which case, copying the files to boot partition manually, is not needed.

echo /media/mmcblk0p1/boot /boot none defaults,bind 0 0 >> /etc/fstab

Loopback image with overlayfs

When you install Alpine in diskless mode, the entire system is loaded into memory at boot. If you want additional storage (for example, if you need more space than offered by your RAM) we need to create loop-back storage onto the SD card mounted with overlayfs.

First, make the SD card writable again and change fstab to always do so:

mount /media/mmcblk0p1 -o rw,remount sed -i 's/vfat\ ro,/vfat\ rw,/' /etc/fstab

Create the loop-back file, this example is 1 GB:

dd if=/dev/zero of=/media/mmcblk0p1/persist.img bs=1024 count=0 seek=1048576

Install the ext utilities:

apk add e2fsprogs

Format the loop-back file:

mkfs.ext4 /media/mmcblk0p1/persist.img

Mount the storage:

echo "/media/mmcblk0p1/persist.img /media/persist ext4 rw,relatime,errors=remount-ro 0 0" >> /etc/fstab mkdir /media/persist mount -a

Make the overlay folders, we are using the /usr directory here, but you can use /home or anything else.

Warning: Overlay workdir needs to be an empty directory on the same filesystem mount as the upper directory. So each overlay must use its own workdir.

mkdir /media/persist/usr mkdir /media/persist/.work_usr echo "overlay /usr overlay lowerdir=/usr,upperdir=/media/persist/usr,workdir=/media/persist/.work_usr 0 0" >> /etc/fstab mount -a

Your /etc/fstab should look something like this:

/dev/cdrom /media/cdrom iso9660 noauto,ro 0 0 /dev/usbdisk /media/usb vfat noauto,ro 0 0 /dev/mmcblk0p1 /media/mmcblk0p1 vfat rw,relatime,fmask=0022,dmask=0022,errors=remount-ro 0 0 /media/mmcblk0p1/persist.img /media/persist ext4 rw,relatime,errors=remount-ro 0 0 overlay /usr overlay lowerdir=/usr,upperdir=/media/persist/usr,workdir=/media/persist/.work_usr 0 0

Now commit the changes: (optionally remove the e2fsprogs, but it does contain repair tools)

lbu_commit -d

Remember, with this setup if you install things and you have done this overlay for /usr, you must not commit the 'apk add', otherwise, while it boots it will try and install it to memory, not to the persistent storage.

If you do want to install something small at boot, you can use apk add and lbu commit -d.

If it is something a bit bigger, then you can use apk add but then not commit it. It will be persistent (in /user), but be sure to check everything you need is in that directory and not in folders you have not made persistent.

Netboot

Netbooting Raspberry Pi 4

The Raspberry Pi 4 bootloader can be configured to boot from the network [1]. Configure the bootloader with at least

BOOT_ORDER=0xf142 TFTP_PREFIX=1

and optionally also

TFTP_IP=x.x.x.x

where x.x.x.x is the IP address of your TFTP server.

If not configuring TFTP_IP in the bootloader, you'll need to configure your DHCP server to advertise the TFTP server IP address. This varies depending on your DHCP server; use the following details if applicable:

Vendor class: PXEClient:Arch:00000:UNDI:002001
Filename: /

The minimal set of files that your TFTP server needs to host are:

bcm2711-rpi-4-b.dtb (from raspberrypi/firmware/master/boot/bcm2711-rpi-4-b.dtb)
cmdline.txt (see below)
config.txt (see below)
fixup4.dat (from raspberrypi/firmware/master/boot/fixup4.dat, alternatively fixup4cd.dat for the cut down version)
initramfs-rpi4 (from alpine/edge/releases/aarch64/netboot/initramfs-rpi4)
start4.elf (from raspberrypi/firmware/master/boot/start4.elf, alternatively start4cd.elf for the cut down version)
vmlinuz-rpi4 (from alpine/edge/releases/aarch64/netboot/vmlinuz-rpi4)

config.txt:

[pi4] kernel=vmlinuz-rpi4 initramfs initramfs-rpi4 arm_64bit=1

cmdline.txt:

modules=loop,squashfs console=ttyAMA0,115200 ip=dhcp alpine_repo=http://dl-cdn.alpinelinux.org/alpine/edge/main modloop=http://dl-cdn.alpinelinux.org/alpine/edge/releases/aarch64/netboot/modloop-rpi4

Instead of using the http://dl-cdn.alpinelinux.org/alpine/edge/releases/aarch64/netboot/ base URL above, pinning to a specific point in time is preferred. Raspberry Pi 4 netboot files are available from https://dl-cdn.alpinelinux.org/alpine/edge/releases/aarch64/netboot-20230329/ onward.

With the above configured the Raspberry Pi 4 should be able to boot from the network without an SD card.

Wireless support with older Alpine images

In Alpine 3.14, the WiFi drivers for the Raspberry Pi were moved from linux-firmware-brcm to the linux-firmware-cypress package (source?). Since the images seem to be an outdated version of the former, Wi-Fi will work during installation, but after the first update it will break. Use the ethernet interface to download the required packages:

apk add linux-firmware-cypress

And reboot.

If you need Wi-Fi, you'll need to download the latest Broadcom drivers to your SD card. (Replace /mnt/sdcard with the correct mount point.)

 git clone --depth 1 https://github.com/RPi-Distro/firmware-nonfree.git
 cp firmware-nonfree/brcm/* /mnt/sdcard/firmware/brcm

Enable the Serial Console

Besides having enable_uart=1 in usercfg.txt, the kernel command-line option console needs to be changed to console=serial0,115200 in cmdline.txt.

From a Linux desktop, connect to it with something like this:

cu -l /dev/ttyUSB0 -s 115200