Editing MBR and GPT

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==Introduction==

The process of starting a computer and loading the operating system is referred to as “the bootstrap process”, or “booting”. The GhostBSD boot process provides a great deal of flexibility in customizing what happens when the system starts, including the ability to select from different operating systems installed on the same computer, different versions of the same operating system, or a different installed kernel.

The GhostBSD boot process differs from the FreeBSD boot process. On this page we will show you the similarities and differences.

==GhostBSD Boot Process==

===Turning on a computer===

====On x86 hardware====
The Basic Input/Output System (BIOS) is responsible for loading the operating system. The BIOS looks on the hard disk for the Master Boot Record (MBR), which must be located in a specific place on the disk. The BIOS has enough knowledge to load and run the MBR, and assumes that the MBR can then carry out the rest of the tasks involved in loading the operating system, possibly with the help of the BIOS.

The code within the MBR ('''[[/boot/]]mbr''' ) is typically referred to as a boot manager, especially when it interacts with the user. The boot manager usually has more code in the first track of the disk or within the file system. Examples of boot managers include the standard GhostBSD/FreeBSD boot manager '''[[/boot/]]boot0''', also called Boot Easy, and ''Grub'', which is used by many Linux® distributions.

If only one operating system is installed, the MBR searches for the first bootable (active) slice on the disk, and then runs the code on that slice to load the remainder of the operating system. When multiple operating systems are present, a different boot manager can be installed to display a list of operating systems so the user can select one to boot.

====GPT bootcode for UFS on BIOS-based computers====

[https://www.freebsd.org/cgi/man.cgi?query=gptboot&sektion=8&manpath=freebsd-release-ports gptboot] is	used on	BIOS-based computers to	boot from a UFS	partition on a GPT-partitioned disk.  '''[[/boot/]]gptboot''' is installed in a Ghost/FreeBSD-boot partition with [https://www.freebsd.org/cgi/man.cgi?query=gpart&sektion=8&apropos=0&manpath=FreeBSD+12.1-RELEASE+and+Ports gpart(8)].

When it starts, gptboot first reads the GPT and determines	which drive and partition to boot from.  If	it  does not find an eligible partition, or if	the user hits a	key within     three seconds, gptboot switches from auto-boot to interactive mode.  Interactive mode allows manual selection of the disk, partition, filename,   and boot option flags, as described in [https://www.freebsd.org/cgi/man.cgi?query=boot&sektion=8&apropos=0&manpath=FreeBSD+12.1-RELEASE+and+Ports boot(8)].

The GPT standard allows a variable	number of partitions, but ''gptboot'' only    boots from	tables with 128	partitions or less.

For normal	usage, the user	does not have to set or	manage any of the partition attributes.	 ''gptboot'' will boot from	the first UFS partition	found.

''gptboot'' first reads the partition table.  All freebsd-ufs partitions with  only the ''bootonce'' attribute set, indicating a failed boot,	are set	to bootfailed.  ''gptboot'' then scans through all of the	freebsd-ufs partitions.  Boot behavior depends on the combination of ''bootme''	and ''bootonce''     attributes	set on those partitions.

If	neither	''bootonce'' nor ''bootme'' attributes are found on any	partitions,   booting is	attempted from the first Ghost/FreeBSD-ufs partition on the disk.

====Bootstrap Process====

By	default, a three-stage bootstrap is employed, and control is automatically passed from the boot	blocks (bootstrap stages one and two) to a   separate third-stage bootstrap program, [https://www.freebsd.org/cgi/man.cgi?query=loader&sektion=8&apropos=0&manpath=FreeBSD+12.1-RELEASE+and+Ports loader(8)].	 This third stage provides more	sophisticated control over the booting process than it is possible to achieve in the boot blocks, which	are constrained	by occupying  limited fixed space on a given disk or slice.

FILES
* [[/boot/]]boot1   first stage bootstrap file
* [[/boot/]]boot2   second stage	bootstrap file
* [[/boot/]]loader  third stage bootstrap

The automatic boot	will attempt to	load '''[[/boot/]]loader''' from partition `a'     of	either the floppy or the hard disk. This is the final stage of Ghost/FreeBSD's kernel bootstrapping process. 

During initialization, loader will	probe for a console and	set the console variable. <br/>
Next, FICL is initialized, the     builtin words are added to	its vocabulary,	and '''[[/boot/]]boot.4th''' is processed.<br/>
After that, '''[[/boot/]]loader.rc''' is processed. These files are processed	through	the include  command, which reads all of them into memory before processing them, making disk changes possible.

GhostBSD/FreeBSD provides for booting from both the older MBR standard and the newer GUID Partition Table (GPT).
Once the kernel boot process is finished, the kernel passes control to the user process [https://www.freebsd.org/cgi/man.cgi?query=init&sektion=8&manpath=freebsd-release-ports init(8)], which is located at ''/sbin/init''.  The '''[[/boot/defaults/loader.conf]]''' states as GhostBSD defaults: ''rc_system="[[OpenRC|openrc]]".''








[[Category:Sysutils]]