Alpine on a Raspberry Pi

2018/03/15

I am trying out the minimal GNU/Linux distribution Alpine Linux on a Raspberry Pi. By default, Alpine for a Raspberry is run from memory and not the SD card.

There is an unofficial guide for disk-based installation at Alpine’s Wiki. The installation process described here is a more detailed version of this guide with inspiration from https://www.rigon.tk/documentation/alpine-raspberry-pi.

Pre installation

I am preparing the SD card on a laptop running Linux Mint.

  1. Download the tarball for the Raspberry Pi. At the time of writing the newest version is alpine-rpi-3.7.0-armhf.tar.gz.

  2. Mount the SD card and determine the mount point with e.g. lsblk(8). In my case:

$ lsblk
NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sdb      8:16   1  14.9G  0 disk
└─sdb1   8:17   1  14.9G  0 part /media/robert/3636-3339

Unmount the partion(s):

sudo umount /dev/sdb1

  1. Create a bootable FAT32 partition with around 150 MB and fill the remainder of the SD card with another partition. Here I am using GNU parted. In interactive mode the FAT32 partition can be created as follows:
sudo parted /dev/sdb

(parted) mklabel msdos
(parted) mkpart primary fat32 1MiB 150MiB
(parted) set 1 boot on
(parted) quit

Alternatively, create the partitions using the shell:

sudo parted --script /dev/sdb mklabel msdos mkpart primary fat32 1MiB 150MiB mkpart primary ext4 151MiB 100%

You can verify that the partition has been created successfully in parted’s interactive mode.

  1. Format the partition as FAT32:
sudo mkfs.vfat -F 32 /dev/sdb1 
  1. Extract the tarball contents to the FAT32 partition:
sudo mkdir /mnt/alpine
sudo mount /dev/sdb1 /mnt/alpine
sudo tar -xzf /path/to/alpine-rpi-3.7.0-armhf.tar.gz --no-same-owner -C /mnt/alpine
sudo umount /mnt/alpine
sudo rmdir /mnt/alpine

Without --no-same-owner I get permission errors from tar. Apparently this is because the SD card is mounted with SMB.

The file /mnt/alpine/config.txt on the SD card containes configurations for multiple Raspberry version. The unnecesarry parts can be remove by changing it to be

disable_splash=0
boot_delay=0
gpu_mem=256
gpu_mem_256=32
kernel=boot/vmlinuz-rpi
initramfs boot/initramfs-rpi

Installation

Insert the SD card into the Raspberry Pi and turn it on. Log in as root with an empty password. Setup the installation by running setup-alpine and save the changes with lbu commit -d. Note that in this disk-less installation changes are only saved if you commit them – this also includes any installed programs.

You can verify that the setup works by rebooting (with reboot or turning off with poweroff). Once the basic setup is done, you can move on to the disk-based installation.

  1. Create the filesystem in /dev/mmcblk0p2 (if it is not already created):

    apk update
    apk add e2fsprogs
    mkfs.ext4 /dev/mmcblk0p2

  2. Do a disk install via a mountpount

    mkdir /stage
    mount /dev/mmcblk0p2 /stage
    setup-disk -o /media/mmcblk0p1/MYHOSTNAME.apkovl.tar.gz /stage
    You will get some error messages from extlinux, but they can be ignored.

At this point I would run out of space on the FAT32 partition, implying that I cannot edit the files required in the remaining steps. However, it turns out that all the disk space is consumed by the local APK cache folder, /media/mmcblk0p1/cache. Delete some files in this folder to free space.

  1. Add this line to /stage/etc/fstab to mount the Raspberry’s boot partition again:

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

  2. Remount /media/mmcblk0p1 to make it writeable:

    mount -o remount,rw /media/mmcblk0p1
    and add “root=/dev/mmcblk0p2” to (the end of) /media/mmcblk0p1/cmdline.txt so that it looks like
    modules=loop,squashfs,sd-mod,usb-storage quiet dwc_otg.lpm_enable=0 console=ttyAMA0,115200 console=tty1 root=/dev/mmcblk0p2

  3. Copy relevant boot files to the FAT32 partition. Here we first backup the previous files:

    cd /media/mmcblk0p1
    mkdir kernel-installer
    mv boot/*rpi kernel-installer/
    cp /stage/boot/* boot/

After rebooting, Alpine starts from mmcblk0p2.

Post installation

First I create a non-root user and add it to the wheel group (to allow changing to root).

adduser -G wheel robert
apk add sudo
visudo
Uncomment the line wheel ALL=(ALL) ALL.

The Raspberry does not have a hardware clock and ALpine informs you of this at boot. In order to add a software clock and delete the hardware clock, run

rc-update add swclock boot
rc-update del hwclock boot
service hwclock stop
service swclock start

An NTP daemon is needed to get the time and if one is not installed, run setup-ntp (in my case it was already running). Save the changes and reboot to check if the setup is working

lbu commit
reboot