Friday, January 23, 2009

grub usage one case

Originally grub is installed in MRB of /dev/sda0. Since I want to replace the disk of /dev/sd0, need to install the same grub in /dev/sda1.

#sudo grub
grub> setup (hd1)
grub> quit

Install Grub
In order to install GRUB as your boot loader, you need to first install the GRUB system and utilities under your UNIX-like operating system (see Obtaining and Building GRUB). You can do this either from the source tarball, or as a package for your OS.

After you have done that, you need to install the boot loader on a drive (floppy or hard disk). There are two ways of doing that - either using the utility grub-install (see Invoking grub-install) on a UNIX-like OS, or by running GRUB itself from a floppy. These are quite similar, however the utility might probe a wrong BIOS drive, so you should be careful.

Also, if you install GRUB on a UNIX-like OS, please make sure that you have an emergency boot disk ready, so that you can rescue your computer if, by any chance, your hard drive becomes unusable (unbootable).

GRUB comes with boot images, which are normally put in the directory /usr/lib/grub/i386-pc. If you do not use grub-install, then you need to copy the files stage1, stage2, and *stage1_5 to the directory /boot/grub, and run the grub-set-default (see Invoking grub-set-default) if you intend to use `default saved' (see default) in your configuration file. Hereafter, the directory where GRUB images are initially placed (normally /usr/lib/grub/i386-pc) will be called the image directory, and the directory where the boot loader needs to find them (usually /boot/grub) will be called the boot directory.

Installing GRUB natively

Caution: Installing GRUB's stage1 in this manner will erase the normal boot-sector used by an OS.

GRUB can currently boot GNU Mach, Linux, FreeBSD, NetBSD, and OpenBSD directly, so using it on a boot sector (the first sector of a partition) should be okay. But generally, it would be a good idea to back up the first sector of the partition on which you are installing GRUB's stage1. This isn't as important if you are installing GRUB on the first sector of a hard disk, since it's easy to reinitialize it (e.g. by running `FDISK /MBR' from DOS).

If you decide to install GRUB in the native environment, which is definitely desirable, you'll need to create a GRUB boot disk, and reboot your computer with it. Otherwise, see Installing GRUB using grub-install.

Once started, GRUB will show the command-line interface (see Command-line interface). First, set the GRUB's root device4 to the partition containing the boot directory, like this:

grub> root (hd0,0)

If you are not sure which partition actually holds this directory, use the command find (see find), like this:

grub> find /boot/grub/stage1

This will search for the file name /boot/grub/stage1 and show the devices which contain the file.

Once you've set the root device correctly, run the command setup (see setup):

grub> setup (hd0)

This command will install the GRUB boot loader on the Master Boot Record (MBR) of the first drive. If you want to put GRUB into the boot sector of a partition instead of putting it in the MBR, specify the partition into which you want to install GRUB:

grub> setup (hd0,0)

If you install GRUB into a partition or a drive other than the first one, you must chain-load GRUB from another boot loader. Refer to the manual for the boot loader to know how to chain-load GRUB.

After using the setup command, you will boot into GRUB without the GRUB floppy. See the chapter Booting to find out how to boot your operating systems from GRUB.

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