Raspberry Pi: Difference between revisions

Revision as of 14:29, 11 December 2019

This tutorial will help you install Alpine Linux on your Raspberry Pi.

Preparation

Download the Alpine for Raspberry Pi tarball. You should be safe using the armhf build on all versions of Raspberry Pi (including Pi Zero and Compute Modules); but it may perform less optimally on recent versions of Raspberry Pi. The armv7 build is compatible with Raspberry Pi 2 Model B. The aarch64 build should be compatible with Raspberry Pi 2 Model v1.2, and is compatible with Raspberry Pi 3 and Compute Module 3.
Create a bootable FAT32 partition on your SD card. You can use a partitioning tool such as gnome-disks or fdisk.
Create a filesystem on the partition with mkdosfs -F 32 /dev/sdX1 (Replace sdX1 with the correct reference to the partition you just created.)
Mount the partition and extract the tarball contents unto it.

Optionally create a usercfg.txt file on the partition to configure low-level system settings. Specifications can be found here. Some interesting values include:

To enable audio: dtparam=audio=on
If you see black edges around your screen after booting the Pi, you can add disable_overscan=1

If you need WiFi to work, you have 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

Installation

Alpine Linux will be installed as diskless mode, hence you need to use Alpine Local Backup (lbu) to save your modifications between reboots. Follow these steps to install Alpine Linux:

Insert the SD card into the Raspberry Pi and turn 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

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

apk update apk upgrade

Don't forget to save the changes:

lbu commit -d

Clock-related error messages

During the booting time, you might notice errors related to the hardware clock. The Raspberry Pi does not have a hardware clock and therefore 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

Since Raspberry Pi does not have a clock, the Alpine Linux needs to know what the time is by using a Network Time Protocol (NTP) daemon. Make sure that you a NTP daemon installed and running. If you are not sure, then you can install NTP client by running the following command:

setup-ntp

The Busybox NTP client might be the most lightweight solution. Save the changes and reboot, once the NTP software is installed and running:

lbu commit -d reboot

After reboot, make sure that the date command outputs the correct date and time.

WiFi on boot

If you have already configured WiFi during the setup, the connection will not return on reboot. You will need to start up a service to automatically connect to the wireless access point.

Run rc-update add wpa_supplicant boot to connect to the wireless access point on boot.
Run it manually with /etc/init.d/wpa_supplicant start.

Enable OpenGL (Raspberry Pi 3)

Remount the boot partition writeable (ie. /media/mmcblk0p1):

mount -o remount,rw /media/mmcblk0p1

Add the following lines to /media/mmcblk0p1/config.txt

dtoverlay=vc4-kms-v3d
gpu_mem=128

256MB gpu_mem is also possible

Install mesa-dri-vc4:

apk add mesa-dri-vc4

Reboot:

lbu_commit -d; reboot

Persistent storage

Loopback image with overlayfs

The install is in diskless mode and forces everything into memory, if you want additional storage we need to create loop-back storage onto the SD 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 doing /usr here, but you can do /home or anything else:

mkdir /media/persist/usr mkdir /media/persist/.work echo "overlay /usr overlay lowerdir=/usr,upperdir=/media/persist/usr,workdir=/media/persist/.work 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 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 and not to the persist 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 do check everything you need is in that directory and not in folders you have not made persistent.

Traditional disk-based (sys) installation

Warning: This isn't yet supported by the Alpine setup scripts for Raspberry Pi. It requires manual intervention, and might break.

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 these: the Raspberry Pi doesn't need this to boot anyway.

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 on shutdown.

Beware, though, that 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 so that manually copy the files to boot partition is not needed.

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

Persistent Installation on Raspberry Pi 3

See this page : https://wiki.alpinelinux.org/wiki/Classic_install_or_sys_mode_on_Raspberry_Pi

See https://web.archive.org/web/20171125115835/https://forum.alpinelinux.org/comment/1084#comment-1084

Troubleshooting

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.

Alternatively, installing haveged, the random numbers generator, would speed up the process :

 apk update 
 apk add haveged
 rc-update add haveged boot
 lbu commit -d
 service haveged start

(Tested on a raspberry pi zero W headless mode, no USB connected, Alpine 3.10.3)

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.