alpine-diskless

Alpine Linux setup with diskless mode for Raspberry Pi

Preparation for Alpine Linux installation

# Prepare SD Card
sudo mkdir /mnt/sdcard
sudo mount /dev/sdc1 /mnt/sdcard

# Extract archive into /mnt/sdcard
sudo tar -xzf alpine-rpi-<version>-aarch64.tar.gz -C /mnt/sdcard

# Download from https://github.com/macmpi/alpine-linux-headless-bootstrap/releases
sudo mv headless.apkovl.tar.gz /mnt/sdcard

nano /mnt/sdcard/wpa_supplicant.conf # For wifi connection

country=FI

network={
	key_mgmt=WPA-PSK
	ssid="mySSID"
	psk="myPassPhrase"
}

sudo mkdir /mnt/sdcard/service
# service executable into /mnt/sdcard/service
sync
sudo umount mnt/sdcard

setup-alpine

setup-alpine
# Proceed with desired options.

# SSH = dropbear

# Disk & Install
none

# Setup ethernet interface
setup-interfaces
eth0
dhcp
done

mkdir -p ~/.ssh
chmod 700 ~/.ssh
touch ~/.ssh/authorized_keys
chmod 600 ~/.ssh/authorized_keys

# For LBU
lbu add /etc/wpa_supplicant/wpa_supplicant.conf
lbu add /etc/dropbear/
lbu add /etc/conf.d/dropbear # Options may be configured there
lbu add ~/.ssh/

lbu commit -d

Configurations

cmdline.txt

modules=loop,squashfs,sd-mod,usb-storage quiet console=tty1

usercfg.txt

gpu_mem=8
dtparam=audio=off
dtoverlay=disable-bt
hdmi_enable=0

OS Upgrade

vi /etc/apk/repositories

/media/mmcblk0p1/apks
http://dl-cdn.alpinelinux.org/alpine/v3.23/main
#http://dl-cdn.alpinelinux.org/alpine/v3.23/community

lbu commit
reboot
cat /etc/os-release
apk update && apk upgrade --available

Services

vi /etc/init.d/service

#!/sbin/openrc-run

name="service"
description="Run service from ramdisk"
command="/mnt/ramdisk/service/service"
command_background=true
pidfile="/run/${RC_SVCNAME}.pid"
    
start_pre() {
    if [ ! -f /mnt/ramdisk/service/service ]; then
        mkdir /mnt/ramdisk/service
        cp /media/mmcblk0p1/service/service /mnt/ramdisk/service || return 1
    fi
}

start() {
    ebegin "Starting ${name}"
    start-stop-daemon --start --exec "${command}" \
        --pidfile "${pidfile}" \
        --background \
        --make-pidfile \
        --stdout /var/log/service.log \
    eend $?
}

Enable service

chmod +x /etc/init.d/service
rc-update add service default
mkdir /opt/service/ # If service saves configuration files or data

LBU

Local backup utility(lbu) is the Alpine Linux tool to manage Diskless Mode installations. For these installations, lbu tool must be used to commit the changes whenever Alpine Package Keeper is used.

When Alpine Linux boots in diskless mode, it initially only loads a few required packages from the boot device. However, local adjustments to what-gets-loaded-into-RAM are possible, e.g. installing a package or adjusting the configuration files in /etc. The modifications can be saved with lbu tool to an overlay file i.e apkovl file that can be automatically loaded when booting, to restore the saved state.

By default, an lbu commit only stores modifications below /etc, with the exception of the /etc/init.d/ directory. If a user was created during the setup-alpine script, that user's home directory is also added to the paths that lbu will backup up. However, lbu add enables modifying that set of included files, and can be used to specify additional files or folders.

lbu add /opt/service/ # If service saves configuration files or data
lbu add /etc/init.d/service
lbu add /etc/wpa_supplicant/ # If using WiFi network
lbu commit

Filesystem in RAM

# For services - This example uses 8MB RAM
echo "tmpfs /mnt/ramdisk tmpfs size=8m,mode=0755 0 0" >> /etc/fstab
# Increase tmp size for lbu - 32MB RAM
echo "tmpfs /tmp tmpfs defaults,noatime,nosuid,nodev,size=32m 0 0" >> /etc/fstab

mount -a

Crontab

crontab -e

# min hour day month weekday command
  1   1    *   *     0       lbu status | grep -q . && /usr/sbin/lbu commit # Backup system every week at Sunday              
  2   4    5   *     *       apk update && apk upgrade -a --no-interactive  # Upgrade packages every month
  3   4    *   *     0       rc-service dropbear restart

Packages

# Unnecessary packages for wifi connection after configuring Ethernet connection
apk del --purge iw libnl3 wpa_supplicant
rc-service networking restart

apk fix
apk cache clean