Alpine and UEFI

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UEFI and BIOS definitions and introduction

In the old days, BIOS (for Basic Input Output System) was how computers booted from the 1980s onwards. But now in newer hardware for devices, servers, laptops and desktops computers the UEFI (for Unified Extensible Firmware Interface) defines a software interface between an operating system and platform firmware into the vendor hardware.

UEFI replaces the BIOS firmware interface originally present in all IBM PC-compatible personal computers, early modern computer's UEFI firmware implementations provide legacy support for BIOS services.

The history so far

Due newer incoming 64-bit incoming processors the older computers boot process are not more possible. It started life on Itanium (Intel's first 64-bit processor) systems. Itanium had no support for 32-bit, and certainly no embedded 80286, so they had to come up with a different system.

All this was driven by a problem in the most extensive and used architecture: x86 32-bit, inclusivelly a new 2019's Skylake i7-6700k still has an 80286 embedded in it because all x86 BIOS strictly only supports 16-bit 8088-derivative processors.

Intel developed the original Extensible Firmware Interface (EFI) specification. Some of the EFI's practices and data formats mirror those from M$ Redmon's OS. In 2005, UEFI deprecated EFI 1.10 (the final release of EFI). The Unified EFI Forum is the industry body that (seems) "manages" the UEFI specification.

Alpine UEFI support

Currently are only in basic form, not all the architectures are complete supported.

The support for EFI System Partition was started in the Alpine 3.7.0 new mayor release, preliminary support in that version does not create the EFI Partition, only has support for existing ones or manually created.

Started in the Alpine 3.8.0 new mayor release support in the installer for the GRUB boot loader was added so now Linux experimental users can play with combinations of solutions and proper UEFI complete installations. Please refer to UEFI_and_BIOS section of this page first.

EFI System Partition are not the complete overall of the UEFI, it's just the need minimal infrastructure to property boot by and UEFI modern machine. See the Alpine UEFI partition mechanics notes section in this page for details.

Please read carefully the UEFI_and_BIOS section of this page.

Minimum Alpine partition sheme

Alpine Linux only require a root partition for system and a swap partition, but, UEFI systems require an EFI system partition. Needs a bootloader program in \EFI\$bootloader.efi on a EFI System Partition, a specially tagged partition. The current status of that mechanics to boot in Alpine Linux are still in development and only basic support to existing mades are provided. See UEFI_mandatory_partition_mechanics for details.

Notes about the boot flags and boot partition

UEFI booting does not involve any "boot" flag, that's it's a need only for BIOS booting. The UEFI booting relies solely on the boot entries in NVRAM. Parted and its front-ends use a "boot" flag on GPT to indicate that a partition is an EFI system partition.

A BIOS boot partition is only required when using GRUB for BIOS booting from a GPT disk. The partition has nothing to do and it must not be formatted with a file system or mounted.

Alpine disk layout for UEFI

You will need a disk layout that your system firmware is capable of booting, you will need a boot partition and a root partition. Other architectures may have different requirements an not all are supported, please read UEFI_mandatory_partition_mechanics for details.

If you don't already know what filesystem format you want your boot partition, choose ext2. The root partition, and any additional partitions or LVM volume groups, may be in any format that the kernel is capable of reading.

UEFI/GPT minimal layout

Mount point Partition Partition type Purpose Recommended size
/boot or /efi /dev/sda1 Boot system partition for EFI 260 MiB
/ /dev/sda2 Alpine Linux root system OS 1–32 GiB
none /dev/sda3 Linux swap memory 1-2Gb

BIOS/MBR minimal layout

Mount point Partition Partition type Purpose Recommended size
/boot /dev/sda1 Boot grub partition (optional) 100 MiB
/ /dev/sda2 Alpine Linux root system OS 1–32 GiB
none /dev/sda3 Linux swap memory 1-2Gb

BIOS/GPT minimal layout

Mount point Partition Partition type Purpose Recommended size
None /dev/sda1 BIOS boot partition 8 MiB
/ /dev/sda2 Alpine Linux root system OS 1–32 GiB
none /dev/sda3 Linux swap memory 1-2Gb

BIOS boot process for newbies

BIOS only supports two methods of booting - loading 448ish bytes of 8088 machine code from the start of a floppy disk, or the same from the start of a fixed IDE disk

BIOS can only assume one boot loader occupying the start of hard drive. So each OS overwrites it with its own boot loader. Messy messy. There's also the 2TB issue I mentioned before

In order to make your drive more useful, it's split up into partitions - chunks of disk which can be treated as independent drives from inside your OS. Ruindows (following on from MS-DOS) only supports one method for partitioning its boot drive on BIOS systems: "MBR"

MBR cannot handle numbers bigger than 2,199,023,255,552. It is impossible to talk about any drive beyond 2TB using MBR layout. So if you're booting from it and use BIOS, you MUST use MBR (because that's all Windows supports) - and you simply can't use any space beyond that if your boot drive is 3TB or bigger.

For now. Ish. Any modern motherboard (some 2011 onwards, all with a Ruindows 8 logo on the box) is using UEFI natively, but most can emulate BIOS enough for you to keep booting with BIOS.

UEFI boot process explained

Well, let's start with installers. It'll read a UDF or FAT32-formatted USB drive or DVD, and look for the file /efi/boot/bootx64.efi and run it. An app, written in the UEFI "OS". It can be anything! Here's classic text adventure Zork, as a UEFI app.

It's possible to make boot media which is valid for both UEFI and BIOS. Unfortunately, in a slightly user-unfriendly twist, you (the user) need to pick the right boot entry. For example, on the wife's PC, a USB stick gets listed as both "UEFI: Sandisk Cruzer Edge" and "USB: Sandisk Cruzer Edge". Just... make sure you pick the right entry. It's impossible to change mode after this point.

It uses a different partitioning system called GPT instead of MBR, and secondly it creates an extra ~100 meg partition called the "EFI System Partition" - a FAT32 partition where the boot loader apps get installed to (no more boot sectors).

Each OS will stick its boot loader somewhere in the ESP, then send a signal to the firmware to write this new loader's location into the CMOS. Each entry installed in this manner will get its own listing in your "boot devices" list on the firmware - so if you installed MACOSX, you'll have "MACOSX Boot Manager" as an entry next to your DVD drive and hard drive after you reboot. This is why you don't do the old "unplug drive A when installing a different OS to drive B" thing, or swap cables, or anything like that. You should only have one ESP, the one on drive A.

UEFI mandatory partition mechanics

Regular UEFI boot has several lists of possible boot entries, stored in UEFI config variables (normally in NVRAM), and boot order config variables stored alongside them. Unfortunately, a lot of PC UEFI implementations have got this wrong and so don't work properly.

The correct way for this to work when booting off local disk is for a boot variable to point to a vendor-specific bootloader program in \EFI\$bootloader.efi on the EFI System Partition (ESP), a specially tagged partition (Some OS's formatted as Fat32.. that's are unnecessary due it's just to able to poor OS's to boot like M$ Redmond OS's). The current status of that mechanics to boot in Alpine Linux are still in development and only basic support to existing made are provided.

What's this infamous "Secure Boot"?

It's a way for your motherboard to prevent tampering of your OS (e.g. boot-sector viruses, or backdoors installed without your knowledge). You can provide a list of certificates you trust, then the firmware enforces that everything involved with the boot process (not just the boot loader, but the OS kernel itself, and all your device firmware like your GPU BIOS) are signed with a trusted key.

Works using cryptographic checksums and signatures. It stops your system from booting unsigned code. You can sign your own, and trust the certificate you used to do that signing. Or you can get the boot code signed by M$ - every motherboard has a small list of pre-trusted certificates which almost (always) includes M$ redmon's certs, which they currently let anyone use for a small fee.

Most of the programs that are expected to run in the UEFI environment are boot loaders, but others exist too. There are also programs to deal with firmware updates before operating system startup (like fwupdate and fwupd), and other utilities may live here too.

How to boot unsigned code?

You must disable Secure Boot. Alpine has no support due there's no Alpine Cert boot! Other Linux distros (mostly enterprise made related) have had. This meant that on many new computer systems, users had to first disable Secure Boot to be able to install and the methods for doing this vary massively from one system to another, making this potentially quite difficult for users.

This are due M$crosoft act as a Certification Authority (CA) for SB, and they will sign programs/bootloaders on behalf of other trusted organizations so that their programs will also run, that of course have a cost.. and there's nothing related to free software but affects to.. There's no Alpine Linux Certification like are with other enterprise related Linux.

Overall notes and conclusions

Currently Alpine UEFI and Secure Boot are very early stage.. enough support was made and enabled but Secure Boot must be disabled due obviously reasons.

BIOS only or compatible old BIOS computers are a most easily way to install Linux in general, that does not need of extra partition layer to boot.. and does not need extra special files into.

UEFI only or newer UEFI computers are very common in nomadays and not so easy to install Alpine linux, that will need extra partition layer to boot.. a extra EFI partition with special files into.

See Also