Architecture

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(Last edited by Zcrayfish on 12 Jan 2024.)

Alpine Hardware Architecture ("arch") Support

Todo: add riscv64

x86 Based

x86 - 32 bit x86 (ia32)
x86_64 - 64 bit x86 (amd64)

ARM Based

See Alpine on ARM.

armhf - 32 bit ARM (hard-float ABI) - ARMv6
armv7 - 32 bit ARMv7
aarch64 - 64 bit ARM - ARMv8

PowerPC Based

ppc64le - 64 bit PowerPC (little-endian)

IBM System Z Based

s390x

Alpine Packaging

Package Building

Alpine Package Building Ports

APKBUILD - Package build scripts
aports - Official Alpine ports git repository

Package Building Tools

abuild

Package Format

Alpine uses packages in the .apk file format.

Package Management Tools

apk - Alpine Package Keeper (see Apk spec for more detail)

Boot Process

Boot Loader

The bootloader is responsible for finding the initfs, cmdline and kernel, and handling execution over to the kernel.

Some bootloaders allow the user to interactively pick which OS or kernel to use (if more than one is available).

EFI

The default setup uses GRUB2.
See also UEFI Secure Boot

BIOS

The default setup uses GRUB2.

Other

Kernel

Versioning

Flavors

lts - long-term support kernel, general purpose
virt - for running under virtual machines
edge - Latest stable kernel
rpi - Raspberry Pi
rpi2 - Raspberry Pi 2 (Alpine ≤v3.18 only, merged with rpi in current versions)
rpi4 - Raspberry Pi 4 (Alpine ≤v3.18 only, merged with rpi in current versions)
ashai - Apple M1

Signing

Command line options

modules="<modules>" - specify list of modules to be loaded by initramfs /init needed to mount real root filesystem.

Initfs

The kernel will decompress the stream of compressed cpio archives passed to it by the 'append' bootloader option to the root of 'rootfs', a tmpfs automatically mounted at '/' by the kernel at boot.

'/init' Script

Not to be confused with /sbin/init(see below)

This script is in the root of the initfs filesystem and is called by the kernel upon completion of its boot process. It is responsible for doing whatever steps are necessary to mount the real root file system to / and hand over control to /sbin/init.

Parses kernel command line options.
Uses nlplug-findfs to discover devices.
[Optionally] prompts for disk encryption secrets and unlocked encrypted partitions.

Initfs Module Handling

Modules required to mount the root filesystem and boot must either built into the kernel or available from with the initramfs filesystem through use of appended initrd cpio.gz files provided by the bootloader.

The /init script will first modprobe the modules specified by the modules= kernel command line option and by the name of the specified rootfs type. It will then load the contents of /etc/modules, which may include module options. Modules may be blacklisted from autoprobing (but NOT explicit insertion!) using the blacklist= kernel command line option which appends blacklist entries to '/etc/modprobe.d/boot-opt-blacklist.conf'.

Minimal Required Set

Todo: /media is not required even tough it is included in the alpine-baselayout

Directory Structure

/ /bin /boot /dev /etc /lib /lib/modules /media /media/cdrom /media/usb /mnt /proc /sbin /sys /usr /usr/bin /usr/sbin

Devices

/dev/null
/dev/console
/dev/kmsg

Mounts

/proc
/sys
/dev (can be disabled?)

Configuration

/etc/passwd
/etc/group
/etc/fstab

Binaries

busybox
apk

Feature Sets

Feature sets consist of lists for the set of modules and files that need to be included in a final initramfs to support the indicated feature.

Init

/sbin/init is the first process to be started in the live system after the initramfs completes its work. It is part of the Busybox package and should not be confused with the /init script mentioned above.

Loading of Kernel Modules

/etc/init.d/modules loads all modules specified in /etc/modules and /(etc|run|usr/lib|lib)/modules-load.d/*.conf