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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installgrub

installgrub(1M)                                                                                                                    installgrub(1M)

NAME

       installgrub - install GRUB in a disk partition or a floppy

SYNOPSIS

       /sbin/installgrub [-fm] stage1 stage2 raw-device

       The installgrub command is an -only program. GRUB stands for GRand Unified Bootloader.

       installgrub  installs  GRUB  stage  1  and  stage  2  files on the boot area of a disk partition. If you specify the -m option, installgrub
       installs the stage 1 file on the master boot sector of the disk.

       The installgrub command accepts the following options:

       -f

           Suppresses interaction when overwriting the master boot sector.

       -m

           Installs GRUB stage1 on the master boot sector interactively.

       The installgrub command accepts the following operands:

       stage1

           The name of the GRUB stage 1 file.

       stage2

           The name of the GRUB stage 2 file.

       raw-device

           The name of the device onto which GRUB code is to be installed. It must be a character device that is readable and writable.  For  disk
           devices,  specify  the  slice  where  the  GRUB  menu  file  is  located.  (For Solaris it is the root slice.) For a floppy disk, it is
           /dev/rdiskette.

       Example 1: Installing GRUB on a Hard Disk Slice

       The following command installs GRUB on a system where the root slice is c0d0s0:

       example# /sbin/installgrub /boot/grub/stage1 
                /boot/grub/stage2 /dev/rdsk/c0d0s0

       Example 2: Installing GRUB on a Floppy

       The following command installs GRUB on a formatted floppy:

       example# mount -F pcfs /dev/diskette /mnt
       # mkdir -p /mnt/boot/grub
       # cp /boot/grub/* /mnt/boot/grub
       # umount /mnt
       # cd /boot/grub
       # /sbin/installgrub stage1 stage2 /dev/rdiskette

       /boot/grub

           Directory where GRUB files reside.

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE         |      ATTRIBUTE VALUE        |
       +-----------------------------+-----------------------------+
       |Availability                 |SUNWcsu                      |
       +-----------------------------+-----------------------------+
       |Interface Stability          |Evolving                     |
       +-----------------------------+-----------------------------+

       boot(1M), fdisk(1M), fmthard(1M), kernel(1M), attributes(5)

       Installing GRUB on the master boot sector (-m option) overrides any boot manager currently installed on the machine. The system will always
       boot the GRUB in the Solaris partition regardless of which fdisk partition is active.

                                                                    24 May 2005                                                    installgrub(1M)