unattended

Unattended system provisioning

Unattended installation comprises of two phases:

1. Installation of OS itself with automatic answers
2. Provisioning of installed OS (application installation, configuration etc.)

It is tightly coupled with Infrastructure as a Code concept.

OS installation

Uses PXE boot, which can roughly be depicted as (BIOS example):

PXE booting relies on platform firmware, its configuration files are different for BIOS and its successor UEFI.

BIOS

Hardware initialization in not exactly standarized manner (as reverse engineered from IBM first implementation).
After POST boots by reading and executing first sector on hard disk. Booting runs in 16-bit processor mode and has only 1MB of space to execute in. Has problems with parallel device initialization. Can boot only from hard disks of size less than 2.1TB
Uses MBR partitioning scheme

UEFI

Has no limitations of BIOS, standarized (by Intel).
Specifies following servies available for OS and OS loader:

System table
Boot time services
Run time services
Console
Additional tables

Boots by loading EFI program files.
Uses GPT partitioning scheme

Debian-based OS installation

Named as: preseeding
Example of preseed with custom partition setup

d-i partman-auto/choose_recipe select expert
d-i partman-auto/expert_recipe string \
boot-root :: \
                2048 2200 4096 ext4 \
                        $primary{ } $bootable{ } \
                        method{ format } format{ } \
                        use_filesystem{ } filesystem{ ext4 } \
                        mountpoint{ / } \
                . \
                1024 1100 1500 ext4 \
                        method{ format } format{ } \
                        use_filesystem{ } filesystem{ ext4 } \
                        mountpoint{ /home }  \
                 . \
                1024 1100 1500 ext4 \
                        method{ format } format{ } \
                        use_filesystem{ } filesystem{ ext4 } \
                        mountpoint{ /var }  \
              .  \
              1024 1030 1056 linux-swap \
                        method{ swap } format{ } \
                .

References

1. https://www.debian.org/releases/stretch/example-preseed.txt
2. https://wikitech.wikimedia.org/wiki/PartMan
3. https://wiki.debian.org/DebianInstaller/Preseed
4. https://www.debian.org/releases/stable/amd64/ch03s06.html.en#UEFI
5. http://fai-project.org/fai-guide/
6. https://www.youtube.com/watch?v=bNL1pd-rwCU
7. https://www.howtogeek.com/56958/htg-explains-how-uefi-will-replace-the-bios/