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i love GNU

BIOS

Basic Input Output System - 1975
Software stored on a small chip on the motherboard - ROM - flash memory
Rewritable ( flash memory )
First software run when computer power on

BIOS steps

Initialize and test the system hardware
Load a bootloader or an operating system
Runtime service for operating system - keyboard, display, input/output device , etc. but it don't use with linux, windows and ...
Config hardware - change boot order - view fan speed - etc

UEFI

Unified Extensible Firmware Interface
Replace with traditional BIOS - 2014
Software interface between an operating system and firmware
Initializing/Booting computer before passing to operting system

Advantages

Faster boot
Runtime service - available for os loader or os
Firmware validation method - which boot code is secure
Better interface
Mouse, Network, ...
Boot from GPT
CMS - compability Support Module - bios-based computer(os installed)

Secure boot

UEFI protocol
Secure "boot code"
Validate program with it's own key
Prevent malware from launching at boot time

Secure boot or restricted boot ?

enable/disable secure boot.
run prgoram's that doesn't have certificate key.
can't install os that doesn't have certificate key.

master boot record

GPT

^* EFI system partition

MBR

Master Boot Record
Boot sector at fist sector of mass storage - preceding the first partition
Contain executable code to run operating system or passing to loader's second stage like grub

MBR Content

Partition table
Bootstarp code - passing to bootable partition loader, ...

MBR information

Number of partition - 4 primary
Size of partition ( 2 TB - max )

Structure of a classical generic MBR
Address		Description		Size (bytes)
Hex	Dec	Description		Size (bytes)
`+000h`	+0	Bootstrap code area		446
`+1BEh`	+446	Partition entry #1	Partition table (for primary partitions)	16
`+1CEh`	+462	Partition entry #2		16
`+1DEh`	+478	Partition entry #3		16
`+1EEh`	+494	Partition entry #4		16
`+1FEh`	+510	`55h`	Boot signature^[a]	2
`+1FFh`	+511	`AAh`	Boot signature^[a]	2
				512

GPT

GUID Partition Table
Replace with MBR
Part of EFI standard
2*64 - max disk size - 128 partition ( could be more than it )

GPT content

sector 0 for mbr protective - GPT header begin from sector 1 from hard disk - entries
copy header and entries at end of the disk

booting: gpt/mbr in bios based computer

Directory	Description
`/`	Primary hierarchy root and root directory of the entire file system hierarchy.
`/bin`	Essential command binaries that need to be available in single user mode; for all users, e.g., cat, ls, cp.
`/boot`	Boot loader files, e.g., kernels, initrd.
`/dev`	Essential devices, e.g., /dev/null.
`/etc`	Host-specific system-wide configuration files There has been controversy over the meaning of the name itself. In early versions of the UNIX Implementation Document from Bell labs, /etc is referred to as the etcetera directory, ^{[ 2 ]} as this directory historically held everything that did not belong elsewhere (however, the FHS restricts /etc to static configuration files and may not contain binaries). ^{[ 3 ]} Since the publication of early documentation, the directory name has been re-explained in various ways. Recent interpretations include backronyms such as "Editable Text Configuration" or "Extended Tool Chest".
`/etc/X11`	Configuration files for the X Window System, version 11.
`/home`	Users'home directories, containing saved files, personal settings, etc.
`/lib`	Libraries essential for the binaries in `/bin/` and `/sbin/` .
`/media`	Mount points for removable media such as CD-ROMs(appeared in FHS-2.3).
`/mnt`	Temporarily mounted filesystems.

`/opt`	Optional application software packages.
`/proc`	Virtual filesystem providing process and kernel information as files. In Linux, corresponds to a procfs mount.
`/root`	Home directory for the root user.
`/run`	Run-time variable data: Information about the running system since last boot, e.g. , currently logged-in users and running daemons.
`/sbin`	Essential system binaries, e.g. , fsck, init, route.
`/tmp`	Temporary files (see also `/var/tmp` ). Often not preserved between system reboots, and may be severely size restricted.
`/usr`	Secondary hierarchy for read-only user data; contains the majority of (multi-)user utilities and applications.
`/usr/bin`	Non-essential command binaries (not needed in single user mode); for all users.
`/usr/include`	Standard include files.
`/usr/lib`	Libraries for the binaries in `/usr/bin/` and `/usr/sbin/` .
`/usr/local`	Tertiary hierarchy for local data, specific to this host. Typically has further subdirectories, e.g. , `bin/` , `lib/` , `share/` .

`/usr/sbin`	Non-essential system binaries, e.g., daemons for various network-services.
`/usr/share`	Architecture-independent (shared) data. example: docs, icons, font, ...
`/usr/src`	Source code, e.g. , the kernel source code with its header files.
`/var`	Variable files—files whose content is expected to continually change during normal operation of the system—such as logs, spool files, and temporary e-mail files.
`/var/cache`	Application cache data. Such data are locally generated as a result of time-consuming I/O or calculation. The application must be able to regenerate or restore the data. The cached files can be deleted without loss of data.
`/var/lib`	State information. Persistent data modified by programs as they run, e.g., databases, packaging system metadata, etc.
`/var/lock`	Lock files. Files keeping track of resources currently in use.
`/var/log`	Log files. Various logs.
`/var/mail`	Users'mailboxes.
`/var/opt`	Variable data from add-on packages that are stored in `/opt/` .
`/var/spool`	Spool for tasks waiting to be processed, e.g. , print queues and outgoing mail queue.
`/var/tmp`	Temporary files to be preserved between reboots.

Linux essential tutorial part 2