Right place to install Linux bootloader Post: 302867801

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Top Forums UNIX for Dummies Questions & Answers Right place to install Linux bootloader Post 302867801 by bakunin on Friday 25th of October 2013 04:41:35 AM

10-25-2013

Registered User

OK, first a few words about the booting process of a PC. That will make it clearer, hopefully:

When a PC starts, the BIOS holds the first program to be loaded. It scans several busses (IDE-controllers, SCSI-controllers, ...) for prospective devices to boot from and creates a list. Then this is worked from top to bottom (though it is possible to exclude certain devices or rearrange list entries - this is a common option in BIOSes).

Every device found that way - usually disks, USB sticks, CD-ROM-drives, diskette drives and so on - is in turn scanned for a so-called "Master boot record". This is a certain disk block, which contains a boot-loader program - if the disk is bootable. If not, then this space is simply left free and the process tries the next device in its list and searches there for a MBR.

If such a boot-loader is found, it is loaded by the BIOS and started. The boot-loader is NOT an OS by itself, it just loads an OS. GRUB, the older lilo and some other boot-loaders work that way. Usually the boot-loader presents a selection of kernels to boot from and a list of root volumes (aka "partitions" to use as the root of the FS - to mount as "/" in case of Unix-systems, as "C:" in case of DOS/Windows-systems or as "[SYS]" in case of VMS-systems.

Once a kernel image and/or boot partition is selected the boot-loader program tries to pass control to an OS-bootstrap program located in certain parts of the selected partition (this is why you need to flag a partition "active" to boot from - this certain space is set apart) and starts that. This in turn loads the OS kernel and the rest is OS specific. Note, that the whole process up to the initialization of the OS kernel happens in the CPUs "real mode", even for protected mode/virtual mode OSes. They have to switch the CPU into their respective mode of operation themselves.

So, to answer your question: yes, you will have to install the boot loader (perhaps "GRUB", less likely "lilo") to the MBR ("/dev/sda", which signifies the disk, rather than "/dev/sdaX", which denotes a certain partition on that disk), otherwise it will not get executed automatically. You need to do that as root, not as normal user, because files involved in the boot process have mostly permissions set to be accessible only by root.

I hope this helps.

bakunin

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LEARN ABOUT FREEBSD

uefi

UEFI(8) 						    BSD System Manager's Manual 						   UEFI(8)

NAME

     UEFI -- Unified Extensible Firmware Interface bootstrapping procedures

DESCRIPTION

     The UEFI Unified Extensible Firmware Interface provides boot- and run-time services to operating systems.	UEFI is a replacement for the
     legacy BIOS on the i386 and amd64 CPU architectures, and is also used on arm64 and ia64.

     The UEFI boot process loads system bootstrap code located in an EFI System Partition (ESP).  The ESP is a GPT or MBR partition with a spe-
     cific identifier that contains an msdosfs(5) FAT file system with a specified file hierarchy.

	   Partition Scheme    ESP Identifier
	   GPT		       C12A7328-F81F-11D2-BA4B-00A0C93EC93B
	   MBR		       0xEF

     The UEFI boot process proceeds as follows:
	   1.	UEFI firmware runs at power up and searches for an OS loader in the EFI system partition.  The path to the loader may be set by an
		EFI environment variable.  If not set, the default is /EFI/BOOT/BOOTX64.EFI.  The default UEFI boot configuration for FreeBSD
		installs boot1.efi as /EFI/BOOT/BOOTX64.EFI.
	   2.	boot1.efi locates the first partition with the type freebsd-ufs, and from it loads loader.efi.
	   3.	loader.efi loads and boots the kernel, as described in loader(8).

     The vt(4) system console is automatically selected when booting via UEFI.

FILES

     /boot/boot1.efi
		   First stage UEFI bootstrap
     /boot/boot1.efifat
		   msdosfs(5) FAT file system image containing boot1.efi for use by bsdinstall(8) and the bootcode argument to gpart(8).
     /boot/loader.efi
		   Final stage bootstrap
     /boot/kernel/kernel
		   default kernel
     /boot/kernel.old/kernel
		   typical non-default kernel (optional)

SEE ALSO

     vt(4), msdosfs(5), boot(8), gpart(8)

HISTORY

     UEFI boot support first appeared in FreeBSD 10.1.

AUTHORS

     UEFI boot support was developed by Benno Rice <benno@FreeBSD.org>, Ed Maste <emaste@FreeBSD.org>, and Nathan Whitehorn
     <nwhitehorn@FreeBSD.org>.	The FreeBSD Foundation sponsored portions of the work.

CAVEATS

     EFI environment variables are not supported by loader(8) or the kernel.

     boot1.efi loads loader.efi from the first FreeBSD-UFS file system it locates, even if it is on a different disk.

     boot1.efi cannot load loader.efi from a ZFS(8) file system.  As a result, UEFI does not support a typical root file system on ZFS configura-
     tion.

BSD
								 October 17, 2014							       BSD