PARTITIONING FOR LFS

AUTHOR: Bruce Dubbs

DATE: 2023-03-13

LICENSE: GNU Free Documentation License Version 1.2

SYNOPSIS: Effecive partitioning a disk drive for LFS

DESCRIPTION:
This hint contains the information about partitioning a disk drive
for effective booting of an LFS system.

ATTACHMENTS:
* None

PREREQUISITES:
* None

HINT:

Booting LFS is no longer as simple as `grub-install  /dev/sda`.  There are
more options and more considerations.  

When starting LFS, the book assumes that you already have a "mainstream" 
version of Linux installed.  That installation may make it difficult to
create the partition where LFS will be built and eventually booted.

There are two issues, the partition table and the organization of partitions
on the hard disk.  A default install of some distributions still use the
deprecated MSDOS partition table instead of the modern GUID Partition Table
(GPT).  In addition, the default install of most distributions use the 
entire disk drive and do not provide any unused disk space.

There are a couple of ways to approach this.  You can reinstall the host
distribution or use a second disk drive.  If installing LFS in a virtual
environment such as qemu or vmware, you will need to install a host
distribution like you would on a single disk system.

Another issue involves the hardware for the machine in use.  Older systems
use a relatively simple BIOS (Basic Input Output System) firmware.  Newer
systems use UEFI (Unified Extensible Firmware Interface) firmware.

A complication of UEFI is that it makes some assumptions about booting
the system.  There are two items to consider.  First is Secure Boot.
In an LFS system this should be disabled.  LFS uses a custom built
kernel and without going into details Secure Boot interferes with that.

The second item is Compatibility Mode.  Some versions of UEFI do
not provide this mode.  Others do.  It is called different things
on different machines.  It can be called CSM (Compatibility Suport
Mode), Legacy Mode, or just provide an Enabled/Disabled selection
for EFI Mode.  Enabling CSM is a user preference item, but is
a bit simplier in an LFS environment.  I recommend using CSM if the
system provides that capability.

The way I recommend installing the host system is to either use a bootable
device and use fdisk or gdisk from the installation system to create a
GPT and a layout similar to this:

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048            4095   1024.0 KiB  EF02  BIOS boot partition
   2            4096          413695   200.0 MiB   8300  /boot
   3          413696         4607999   2.0 GiB     8200  swap
   4         4608000        46551039   20.0 GiB    8300  debian

If a UEFI system is desired or required, the layout should look like this:

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048          411647   200.0 MiB   EF00  EFI System
   2          411648          821247   200.0 MiB   8300  /boot
   3          821248         5015551   2.0 GiB     8200  swap
   4         5015552        46958591   20.0 GiB    8300  debian

If you are installing on a second disk from an established linux
installation, you only need the first two partitions above. In 
either case you will create the new LFS partition in Section 2.4 
of the book. You can use a swap partition or other separate 
partitions from the first disk.

The important thing is that a separate /boot partition allows a single
location for GRUB to find all the files needed for multiple installations.
It just makes configuring GRUB easier.

I'll note here that I like to format the /boot partition as ext2 with
mkfs.ext2 -m0 /dev/sda2 (or /dev/nvme0n1p2 in the case of an m.2 SSD drive)

The reason for ext2 with no reserved blocks is that everything on /boot
is owned by root and is rarely written so there is no real need for a journal.

One last point is that the partitions above have names assigned.  These
can be added at any time with gdisk or the expert mode of fdisk.  The names
can be useful later when configuring GRUB.

Note: The name 'debian' above is just a label and can be any text string.
      In this case it regresents the partition where a standard distribution
      can be installed as a starting point for building your LFS system..

CHANGELOG:
[2023-03-13]
    Initial hint.
