GNU GRUB (0.97) Simplified for Newbies
by
Joydeep Bakshi
12-NOV-2007

Copyright and License

Copyright©2007 by Joydeep Bakshi. This material may be distributed only subject to the terms and conditions set forth in the Open Content License, v1.0 or later (the latest version is presently available at opencontent.org ).


Credits

GRUB originated in 1995 when Erich Boleyn was trying to boot the GNU Hurd with the University of Utah's Mach4 microkernel (now known as GNU Mach). Erich and Brian Ford designed the Multiboot Specification, because they were determined not to add to the large number of mutually-incompatible PC boot methods.

Erich then began modifying the Free BSD boot loader so that it would understand Multiboot. He soon realized that it would be a lot easier to write his own boot loader from scratch than to keep working on the Free BSD boot loader, and so GRUB was born.

Erich added many features to GRUB, but other priorities prevented him from keeping up with the demands of its quickly-expanding user base. In 1999, Gordon Matzigkeit and Yoshinori K. Okuji adopted GRUB as an official GNU package, and opened its development by making the latest sources available via anonymous CVS.

What is GNU GRUB ?

GNU GRUB ("GRUB" for short) is a boot loader from the GNU Project. GNU GRUB is a very powerful boot loader, which can load a wide variety of free operating systems, as well as proprietary operating systems with chain-loading. It can be used to select from different kernel images available on a particular operating system's partitions, as well as to pass boot-time parameters to such kernels.

GNU GRUB developed from a previous package called the GRand Unified Bootloader. The GNU operating system uses GNU GRUB as its boot loader, as do most general-purpose Linux distributions.

In this tutorial I simply mention GRUB to indicate GNU GRUB


MBR, Boot-loader and Boot-sector

The very first sector (512 bytes) of computer's hard disk is called MBR or Master Boot Record. Computer's BIOS is generally programmed to read the code at MBR during booting to know where to look next. MBR is divided into three sections as below.

MBR

The first sector of a partition is known as the 'boot sector'. The first sector of a partition may or may not have any bootloader's code


GRUB stage1, stage1.5 and stage2

stage1

The 446 byte area of the bootloader is really too small for any decent boot loader to fit into. That's why a small amount of code called the 'IPL' or Initial Program Loader is installed there by GRUB. 'First stage' of the boot loader or stage1 is name for the same code. IPL or first stage of a bootloader tells the BIOS where on the hard disk to go looking for the rest part of the boot loader.

stage1.5 (optional)

e2fs_stage1_5, fat_stage1_5, ffs_stage1_5, jfs_stage1_5, minix_stage1_5, reiserfs_stage1_5, vstafs_stage1_5, xfs_stage1_5 are called Stage1.5, because they serve as a bridge between stage1 and stage2. stage1.5 is loaded by stage1 and stage1.5 loads stage2. The difference between stage1 and stage1.5 is that the former doesn't understand any file-system while the latter understands file-system (e.g. e2fs_stage1_5 understands ext2fs). So you can move the stage2 image to another location safely, even after GRUB installation.

stage2

stage2 contains most of the GRUB logic. It loads the menu.lst file and executes the statements. If there is no menu.lst then it starts the GRUB shell interface.


GRUB boot process

When a computer is turned on the computer's BIOS reads (after a successful POST) the master boot record (MBR) from Hard disk.

The MBR contains GRUB stage1. The function of stage1 is to find either stage1.5 or stage2, and pass control over to them. stage1 finds stage1.5 or stage2 by means of physical block addresses that are encoded into the stage1 when GRUB is installed.

stage1.5 is not strictly required. When used, stage1.5 will receive control from stage1, and then pass control over to stage2. stage1.5 understands the file system hence capable of locating stage2 as a file within a file system, rather than the physical block addresses that stage1 uses. If the physical location of the stage2 file changes, stage1.5 will still be able to find it via the file system, while stage1 can't. GRUB has several stage1.5 images available. Each of these images understands one file system, and they are named accordingly. The decision to install (or not) stage1.5 is made by the GRUB installation code, depending on whether or not there is room for it. stage1.5 is too large to fit into a single 512 byte sector, so there is not always a place to put it. stage1.5 can be installed into the area right after an MBR (in the first 30 kilobytes of hard disk immediately following the MBR) or installed to a ReiserFS partition.

stage2 is the core of GRUB and contains the GRUB shell. It is the component which displays the boot menu from menu.lst (usually located at /boot/grub/menu.lst). Once the OS has been selected in the menu GRUB either loads the associated kernel into the memory and passes control on to the kernel or call another loader using chain loading if the operating system required so. If there is no menu.lst then stage2 enters the GRUB shell command prompt.


Boot-loader or IPL (Stage 1) Backup and Restore

The command below creates a backup of the Boot-loader (446 bytes) in my home directory 

  
dd if=/dev/hda of=/home/joy/17Oct2007_Backup_MBR bs=446 count=1

1+0 records in
1+0 records out
446 bytes transferred in 0.023787 seconds (18750 bytes/sec)

save the file in a CD, Floppy or Pen drive. If somehow the MBR will be modified by any application the boot-loader will be modified also. Fixing the boot-loader will restore the system If the partitions are unchanged. Boot the system with a Live Linux CD and mount the media where you save the backup. Now restore the previous boot-loader with the command. 

 dd if=/<path>/17Oct2007_Backup_MBR of=/dev/hda bs=446 count=1
 
 NOTE : Replace the <path> with your actual backup path


Never backup the entire MBR

It is quite possible to make the backup of entire MBR, 512 bytes. This will also keep the record of partition table. If you re-partition your disk later and restore the previous backup of MBR; it will then not match with the recent partition table as well as file system and make the disk un-readable. In this situation you have to repartition and reformat the disk. So never backup the entire MBR but only the boot-loader.

stage1


Disk numbering method

GRUB follows a different numbering system than the linux device node

First floppy disk drive = (fd0)
First hard drive = (hd0)
Second hard drive = (hd1)
... and so on

First partition = 0
second partition = 1
.... and so on

1st partition on first hard drive = (hd0,0)
10th partition on first hard drive = (hd0,9)
3rd partition on second hard drive= (hd1,2)

Hence we can say that

1st partition on first hard drive = (hd0,0) in GRUB = /dev/hda1 in Linux device node
2nd partition on second hard drive = (hd1,1) in GRUB = /dev/hdb2 in Linux device node
etc...........


Disk investigation with GRUB shell

GRUB's shell interface supports Tab completion. We can use this feature to investigate disk attached with the computer.

grub> null (
and pressing the Tab shows in my system 

grub> null (
 Possible disks are: fd0 hd0 hd1 cd

It is also possible to know the partition on say hd0. To do that we have to type (hd0, (comma) and press Tab. Here is the result 

grub> null (hd0,
 Possible partitions are:
 Partition num: 0, Filesystem type unknown, partition type 0x7
 Partition num: 1, Filesystem type unknown, partition type 0x82
 Partition num: 2, Filesystem type is reiserfs, partition type 0x83
 Partition num: 3, Filesystem type is xfs, partition type 0x83

Confirm this output with geometry command in grub shell 

grub> geometry (hd0)
drive 0x80: C/H/S = 16383/255/63, The number of sectors = 78242976, /dev/hda
 Partition num: 0, Filesystem type unknown, partition type 0x7
 Partition num: 1, Filesystem type unknown, partition type 0x82
 Partition num: 2, Filesystem type is reiserfs, partition type 0x83
 Partition num: 3, Filesystem type is xfs, partition type 0x83

Important files

File name Possible location Purpose
device.map /boot/grub/device.map
describes relationship between Linux and GRUB drive designations.created by 'grub-install' if file doesn't already exist in /boot/grub
menu.lst /boot/grub/menu.lst displays the GRUB boot menu
grub /sbin/grub GRUB shell that runs from within Linux. GRUB can be installed or reinstalled from here
grub-install /sbin/grub-install Script that invokes /sbin/grub and installs GRUB to a specified location.

Also generates device.map file and populates /boot/grub with GRUB image files on first install
update-grub /sbin/update-grub

Specific to Debian and Debian- based systems

 Script that automatically generates and updates
stage1 /boot/grub/stage1 boot sector image file containing initial boot code.Gets installed in MBR, partition boot sector, or floppy boot sector
stage2 /boot/grub/stage2 Core image file for GRUB. Executes GRUB shell and menu interface.
*_stage1_5 /boot/grub/*_stage1_5 A set of intermediate stage 1.5 image files, each one specific to just one file system. Locates Stage 2 via the file system it knows. Is embedded outside of any file system

Find partition having Linux kernel 

grub> find /vmlinuz
 (hd0,2)

you may see multiple partitions if you have multiple linux installed in your box. If the kernel has some other name than vmlinuz, that partition will not be shown.


Find root partition 

grub> find /sbin/init
 (hd0,2)

You may see multiple partitions if you have multiple linux installed in your box.


Check the contains of a partition

GRUB shell has the intelligence to show the contains of a partition. Say we like to see the root partition which is (hd0,2) in my machine. "null (hd0,2)/" and then pressing a Tab will show us the needed information. 

grub> null (hd0,2)/
 Possible files are: bin dev etc lib mnt opt srv tmp sys var usr 
 boot home proc sbin root cdrom .reiserfs_priv initrd vmlinuz

We can go further and check the /opt directory by "null (hd0,2)/opt/" and pressing Tab after 

grub> null (hd0,2)/opt/
 Possible files are: vim71 vim-7.1.tar.bz2 cdrtools-beta.tar.gz
 modding hackl7 advanced_software schily kmobiletools-0.5_beta1

GRUB supports "cat" command too. we can check menu.lst as below 

grub> cat (hd0,2)/boot/grub/menu.lst


Creating GRUB bootable CD-ROM

GRUB supports the no emulation mode in the El Torito specification. Hence we can use the whole CD-ROM from GRUB.
http://orgs.man.ac.uk/documentation/grub/grub_fot.html#FOOT5

For booting from a CD-ROM, GRUB uses a special stage2 called stage2_eltorito. We need only this file to make bootable CD-ROM. A config file `menu.lst' is optional. We don't need to use `stage1' or `stage2', because El Torito is quite different from the standard boot process.

1> Make a directory for the bootable image, say, `CD_GRUB'

mkdir CD_GRUB

2> Make a directory for GRUB

mkdir -p CD_GRUB/boot/grub

3> Copy the file `stage2_eltorito' . In debian it is located at /lib/grub/i386-pc/

cp /lib/grub/i386-pc/stage2_eltorito CD_GRUB/boot/grub

4> If desired, make the config file `menu.lst' under `CD_GRUB/boot/grub' or copy th existing one like

cp /boot/grub/menu.lst CD_GRUB/boot/grub

The 'savedefault' command in each operating system's boot entry cause GRUB not to work from a CD. The 'savedefault' command in a hard-disk writes to a file in /boot/grub named 'default', and records the last system that was booted. We cannot use this when running GRUB from a CD, because we can't write changes to a CD with GRUB. So we need to delete all instances of the savedefault command.

5> Now make a ISO9660 image file like this

mkisofs -R -b boot/grub/stage2_eltorito -no-emul-boot \
-boot-load-size 4 -boot-info-table -o cd_grub.iso CD_GRUB

-boot-load-size 4 bit is required for compatibility with the BIOS on many older machines. 

6> Burn the created .iso image. mkisofs has already set up the disc to boot from the boot/grub/stage2_eltorito file.


Creating GRUB bootable Floppy

We have to install both stage1 and stage2 in the Floppy disk. Grub files are resided at /lib/grub/i386-pc/ in debian.

Method - 1

1> cd /lib/grub/i386-pc/

2> stage1 installation 

dd if=stage1 of=/dev/fd0 bs=512 count=1

1+0 records in
1+0 records out
512 bytes transferred in 1.152603 seconds (444 bytes/sec)

3> stage2 installation 

dd if=stage2 of=/dev/fd0 bs=512 seek=1

211+1 records in
211+1 records out
108168 bytes transferred in 6.406743 seconds (16883 bytes/sec)

Warning : This procedure will destroy stored data on the floppy


Method - 2 (using grub-floppy command)

grub-floppy is a program to build a generic grub boot disc. The boot disc when booted provides the grub command line. grub-floppy will create a more generic floppy only limited by architecture

grub-floppy /dev/fd0


Method - 3 (Computer specific boot floppy with /boot/grub)

We can also create a GRUB boot floppy with a file system and menu.lst Like below. ( be super user first )

1> mke2fs /dev/fd0 (creating ext2 file system on floppy)
2> mount -t ext2 /dev/fd0 /mnt/floppy (mounting the floppy at /mnt/floppy)
3> grub-install --root-directory=/mnt/floppy fd0 (Installing GRUB and creating /boot/grub in the floppy)
4> cp /boot/grub/menu.lst /mnt/floppy/boot/grub/ (copy menu.lst)
5> umount /mnt/floppy (floppy is ready, unmount it)


Method - 4 (by GRUB shell, non-interactive mode, also have /boot/grub)

Be super user first

1> mke2fs /dev/fd0
2> mount -t ext2 /dev/fd0 /mnt/floppy
3> mkdir /mnt/floppy/boot
4> cp -R /boot/grub /mnt/floppy/boot
5> /sbin/grub --batch --device-map=/dev/null <<EOF
device (fd0) /dev/fd0
root (fd0)
setup (fd0)
quit
EOF

Step 5 is actually a batch mode of grub shell interface. Here is the output of step 5 

debian:# /sbin/grub --batch --device-map=/dev/null <<EOF
> device (fd0) /dev/fd0
> root (fd0)
> setup (fd0)
> quit
> EOF


 GNU GRUB version 0.97 (640K lower / 3072K upper memory)

 [ Minimal BASH-like line editing is supported. For the first word, TAB
 lists possible command completions. Anywhere else TAB lists the possible
 completions of a device/filename. ]
grub> device (fd0) /dev/fd0
grub> root (fd0)
 Filesystem type is ext2fs, using whole disk
grub> setup (fd0)
 Checking if "/boot/grub/stage1" exists... yes
 Checking if "/boot/grub/stage2" exists... yes
 Checking if "/boot/grub/e2fs_stage1_5" exists... yes
 Running "embed /boot/grub/e2fs_stage1_5 (fd0)"... failed (this is not fatal)
 Running "embed /boot/grub/e2fs_stage1_5 (fd0)"... failed (this is not fatal)
 Running "install /boot/grub/stage1 (fd0) /boot/grub/stage2 p /boot/grub/menu.lst"... succeeded
Done.
grub> quit

You can modify/delete menu.lst from /mnt/floppy/boot/ or keep it to get computer specific menu

6> umount /mnt/floppy

Method - 5 (by GRUB shell, interactive mode, have /boot/grub)

Be super user first

1> mke2fs /dev/fd0
2> mount -t ext2 /dev/fd0 /mnt/floppy
3> mkdir /mnt/floppy/boot
4> cp -R /boot/grub /mnt/floppy/boot
5> umount /mnt/floppy
6> Fire up GRUB shell interface and execute root (fd0) 

grub> root (fd0)
 Filesystem type is ext2fs, using whole disk

7) Install GRUB by setup (fd0) 

grub> setup (fd0)
 Checking if "/boot/grub/stage1" exists... yes
 Checking if "/boot/grub/stage2" exists... yes
 Checking if "/boot/grub/fat_stage1_5" exists... yes
 Running "embed /boot/grub/fat_stage1_5 (fd0)"... failed (this is not fatal)
 Running "embed /boot/grub/fat_stage1_5 (fd0)"... failed (this is not fatal)
 Running "install /boot/grub/stage1 (fd0) /boot/grub/stage2 p /boot/grub/menu.lst
 "... succeeded
Done.

8) Exit from GRUB

You can modify/delete menu.lst from /mnt/floppy/boot/ or keep it to get computer specific menu

Creating GRUB bootable USB pen drive

Be super user.

Identify the device node which your system assigns to the USB pen drive. Execute tail -f /var/log/messages and then plugin the USB drive. Here is mine. 

debian:# tail -f /var/log/messages

SCSI device sda: 248321 512-byte hdwr sectors (127 MB)
sda: Write Protect is off
SCSI device sda: 248321 512-byte hdwr sectors (127 MB)
sda: Write Protect is off
 sda: sda1
Attached scsi removable disk sda

So /dev/sda is the device node for USB pen drive and /dev/sda1 is pointing the partition in that drive.

Now create a directory and mount the USB drive there.
mkdir /mnt/USB_drive
mount -t vfat /dev/sda1 /mnt/USB_drive
The file system of my USB pen drive is FAT that's why I am using -t vfat. Change the file system to suit your USB drive.

Identify the drive number GRUB assigns to the USB drive. Here is mine 

grub> null (
 Possible disks are: fd0 hd0 hd1 cd

Here hd1 is my USB drive as GRUB recognized

Method - 1  (with /boot/grub)

1> Install GRUB on the USB drive by executing
grub-install --root-directory=/mnt/USB_drive hd1 


debian:# grub-install --root-directory=/mnt/USB_drive hd1
Probing devices to guess BIOS drives. This may take a long time.
Installation finished. No error reported.
This is the contents of the device map /mnt/USB_drive//boot/grub/device.map.
Check if this is correct or not. If any of the lines is incorrect,
fix it and re-run the script `grub-install'.

(fd0) /dev/fd0
(hd0) /dev/hda
(hd1) /dev/sda

2> (Optional) Copy the menu.lst to get computer specific menu
cp /boot/grub/menu.lst /mnt/USB_drive/boot/grub/

3> Confirm that USB drive has /boot/grub 

grub> find /boot/grub/stage1
 (hd0,2)
 (hd1,0)

4> Unmount the drive
unmount /mnt/USB_drive

Method - 2 (using interactive GRUB shell, also have /boot/grub)

1> mkdir /mnt/USB_drive/boot
2> cp /boot/grub /mnt/USB_drive/boot
3> umount /mnt/USB_drive
4> Fire up the GRUB shell and execute root (hd1,0) 

grub> root (hd1,0)
 Filesystem type is fat, partition type 0x6

5> Install GRUB by setup (hd1) 

grub> setup (hd1)
 Checking if "/boot/grub/stage1" exists... yes
 Checking if "/boot/grub/stage2" exists... yes
 Checking if "/boot/grub/fat_stage1_5" exists... yes
 Running "embed /boot/grub/fat_stage1_5 (hd1)"... 15 sectors are embedded.
succeeded
 Running "install /boot/grub/stage1 (hd1) (hd1)1+15 p (hd1,0)/boot/grub/stage2
 /boot/grub/menu.lst"... succeeded
Done.

6> Exit from GRUB

You can modify/delete menu.lst from /mnt/floppy/boot/ or keep it to get computer specific menu

Method - 3  (by non-interactive mode of GRUB shell)

1> mkdir /mnt/USB_drive/boot
2> cp /boot/grub /mnt/USB_drive/boot
3> umount /mnt/USB_drive
4> Here is the batch command for USB drive

/sbin/grub --batch --device-map=/dev/null <<EOF
device (hd1) /dev/sda
root (hd1,0)
setup (hd1)
quit
EOF 

debian:# /sbin/grub --batch --device-map=/dev/null <<EOF
> device (hd1) /dev/sda
> root (hd1,0)
> setup (hd1)
> quit
> EOF


 GNU GRUB version 0.95 (640K lower / 3072K upper memory)

 [ Minimal BASH-like line editing is supported. For the first word, TAB
 lists possible command completions. Anywhere else TAB lists the possible
 completions of a device/filename. ]
grub> device (hd1) /dev/sda
grub> root (hd1,0)
 Filesystem type is fat, partition type 0x6
grub> setup (hd1)
 Checking if "/boot/grub/stage1" exists... yes
 Checking if "/boot/grub/stage2" exists... yes
 Checking if "/boot/grub/fat_stage1_5" exists... yes
 Running "embed /boot/grub/fat_stage1_5 (hd1)"... 15 sectors are embedded.
succeeded
 Running "install /boot/grub/stage1 (hd1) (hd1)1+15 p (hd1,0)/boot/grub/stage2 /boot/grub/menu.lst"... succeeded
Done.
grub> quit

You can delete menu.lst from /mnt/USB_drive/boot/ or keep it to get computer specific menu

stage1 and stage2 on different media
PC specific GRUB bootable Floppy/USB with stage1 only

stage1 will reside in the boot able Floppy or USB drive. And this stage1 will call stage2 located in the Hard disk.

Method - 1 (using grub-install command)

We can do this with grub-install like
grub-install /dev/fd0 for floppy

Method - 2 (using GRUB shell)

Within GRUB shell we have to first find out the hard disk partition having /boot/grub to set root device and then execute
root (hd0,2)
setup (fd0)

Method - 3 (using batch mode of GRUB shell)

With GRUB batch mode
/sbin/grub --batch <<EOF
root (hd0,2)
setup (fd0)
quit
EOF


GRUB Rescue in 3 steps

After repartitioning the hard disk by gparted; stage1 may not find stage2 or installing windows after linux modify the MBR with Windows MBR. What ever may be the situation GRUB can be recovered with three easy steps.

Boot the system with a Live Linux disk and execute "grub" command to get its shell interface

Step-1

Find out the device which contains the stage1. Generally stage1 resides at /boot/grub/stage1 (in debian too). If your distro has a different path search accordingly. 

grub> find /boot/grub/stage1
 (hd0,2)


Step-2

Set the GRUB's root device to the partition containing the boot directory. ( see the command in Step-1 ) 

grub> root (hd0,2)
 Filesystem type is reiserfs, partition type 0x83


Step-3

Install the GRUB boot loader (stage1) on the Master Boot Record (MBR) of the first drive 

grub> setup (hd0)
 Checking if "/boot/grub/stage1" exists... yes
 Checking if "/boot/grub/stage2" exists... yes
 Checking if "/boot/grub/reiserfs_stage1_5" exists... yes
 Running "embed /boot/grub/reiserfs_stage1_5 (hd0)"... 18 sectors are embedded.
succeeded
 Running "install /boot/grub/stage1 (hd0) (hd0)1+18 p (hd0,2)/boot/grub/stage2
 /boot/grub/menu.lst"... succeeded
Done.

Restart the machine with out Live Linux disk


What is SUPER GRUB DISK ?

Super GRUB Disk has features that allow users to execute GRUB commands through menu interface and without prior knowledge about GRUB commands that only advanced users who have studied and practiced GRUB commands could do before. One can select what he wants to do from simple menus. Super GRUB Disk also helps to teach what GRUB commands can be used for.

Super GRUB Disk is used for solving many types of bootloader problems. Users without knowing GRUB's Commands can use Super GRUB Disk to fix bootloader problem.

Super GRUB is available as CD, Floppy and Pen drive image.
http://geocities.com/supergrubdisk/


Importance of device.map file

GRUB guesses BIOS devices and stores the result in device.map It is created during installation of GRUB.

When GRUB is used as boot-loader; device.map is useless. hd0 is the first hard disk given by the bios, hd1 is the second... and so. But under Linux environment grub needs to know which linux device correspond to which grub device.

After adding or removing any disk drive from the system, we can edit device.map to add or remove corresponding entry for that particular drive as well as we can also correct any entry in the file if GRUB can't generate the right combination.

grub-install is able to regenerate the device.map with --recheck
Here is my /boot/grub/device.map

(hd0) /dev/hda

After adding Floppy and pen drive I executed (as root)
grub-install --recheck /dev/hda 

debian:# grub-install --recheck /dev/hda
Probing devices to guess BIOS drives. This may take a long time.
Installation finished. No error reported.
This is the contents of the device map /boot/grub/device.map.
Check if this is correct or not. If any of the lines is incorrect,
fix it and re-run the script `grub-install'.

(fd0) /dev/fd0
(hd0) /dev/hda
(hd1) /dev/sda

and now the modified device.map has

(fd0) /dev/fd0
(hd0) /dev/hda
(hd1) /dev/sda


Boot Manually from GRUB's shell interface

When MBR (stage1) is modified by the windows MBR or corrupted; it is still very much possible to boot existing linux kernel. Boot the machine from a Floppy/CD or Pen drive and within GRUB shell follow the steps below

Step-1    >>>>>> Find device and partition having vmlinuz <<<<<< 

grub>find /vmlinuz
(hd0,2)


Step-2    >>>>>> Set GRUB's root device <<<<<< 

grub> root (hd0,2)
 Filesystem type is reiserfs, partition type 0x83


Step-3    >>>>>> Point to the kernel <<<<<< 

grub> kernel /vmlinuz
 [Linux-bzImage, setup=0x1e00, size=0x17c244]

We can also execute
kernel /vmlinuz root=/dev/hda3
to manually set the '/' (root partition); which contains the /sbin/init file
Recall that /dev/hda3 in linux is (hd0,2) in GRUB


Step-4    >>>>>> Point to the initrd <<<<<<

Skip this step if there is no intird; like in case of custom kernel 

grub> initrd /initrd.img
 [Linux-initrd @ 0x1f96a000, 0x675773e bytes]


Step-5    >>>>>> Boot the kernel <<<<<< 

grub> boot_
uncompressing linux... OK, booting the kernel


Skip Manual booting by calling menu.lst and get GUI interface

Why manual booting ? If menu.lst is there just call it by configfile to get the GUI interface. 

grub> configfile (hd0,2)/boot/grub/menu.lst

And this gives you the GUI interface :-)


GRUB GUI configuration with menu.lst file


Basic configuration 


# foreground/background text_color highlighted_color 
color green/black white/black

# Set a timeout, in seconds, before automatically booting the default entry
timeout 20 

# Default entry; Count from 0
default 1 

# Fallback entry.
#if, for any reason, the default entry doesn't work
# fall back to the "fallback"
fallback 2

#Entry 0 
title Ram tester
root (hd0,2)
kernel /boot/memtest86+-1.70.bin
boot

# Entry 1 
title Debian GNU/Linux, kernel 2.6.17 
root (hd0,2)
kernel /boot/vmlinuz-2.6.17 root=/dev/hda3 ro 
boot

# Entry 2 
title Debian GNU/Linux, kernel 2.6.17 (recovery mode)
root (hd0,2)
kernel /boot/vmlinuz-2.6.17 root=/dev/hda3 ro single
boot

# Shutdown
title Shutdown PC
halt

Protection with Encrypted Password 

Generate md5 password with in GRUB shell.  md5crypt is the command to do the same 

grub> md5crypt
Password: ************
Encrypted: $1$j4fjD$pegn7h0etNea5vN18/J1w/

Now see how to protect GRUB shell interface, edit mode and also how to protect GRUB entries with different passwords. 

# foreground/background text_color highlighted_color 
color green/black white/black

# Set a timeout, in seconds, before automatically booting the default entry
timeout 20

########################
# This password protects the GRUB shell interface
# and edit mode
password --md5 $/ee33x434d$dsqasd/wc 
########################

# Default entry; Count from 0
default 1 

# Fallback entry.
#if, for any reason, the default entry doesn't work
# fall back to the "fallback"
fallback 2

#Entry 0 
title Ram tester
root (hd0,2)
kernel /boot/memtest86+-1.70.bin
boot

# Entry 1 
title Debian GNU/Linux, kernel 2.6.17 
root (hd0,2)
kernel /boot/vmlinuz-2.6.17 root=/dev/hda3 ro 
boot
#############################
# Password protected entry
title Debian GNU/Linux, kernel 2.6.17 (recovery mode)
# This password is required to boot this kernel
password --md5 $1$j4fjD$pegn7h0etNea5vN18/J1w/ 
root (hd0,2)
kernel /boot/vmlinuz-2.6.17 root=/dev/hda3 ro single
boot
##############################
# Shutdown
title Shutdown PC
halt

You can create multiple passwords for multiple entries, so that particular entry will have unique password. When you boot the protected entry it asks for the password

Pressing <p> at the boot menu also asks a password. This password is for enabling the GRUB shell interface and edit mode

Splash image

There is no splashimage support in GRUB-0.97. You have to patch the source code to get it. debian is shipped with patched GRUB-0.97 to support splashimage.

"splashimage" feature displays a nice image at boot time while user selects the OS/kernel image to load. splashimage must be
1> xpm.gz format
2> 640x480 resolution
3> 14 colors

The operating system's graphics drivers not be in operation when GRUB displays splashimage. Therefore GRUB counts on the video capabilities of the BIOS. Most computer's BIOSes can't handle fancy, high quality images, so splashimage is limited to an image size of 640x480 pixels and a 14 color display 

# Display splash image 
splashimage=(hd0,2)/boot/grub/splashimage/skull.xpm.gz
foreground ffff00
background 000000

# splashimage doesn't work with color syntax
# Disable color syntax if there is any 
# color green/black white/black

Below is a little shell script which I design to check the splashimage support in GRUB. 

SPLASHSUPPORT=0
IMAGE="splashimage"
SETTING=0
# Check if stage2 has splashimage support
if [ -f /boot/grub/stage2 ]; then
 grep -ia $IMAGE /boot/grub/stage2 > /dev/null 2>&1
    if [ "$?" -eq 0 ]; then
 SPLASHSUPPORT=1
 echo "stage2 supports splashimage"
   fi
fi
# Check menu.1st file for splashimage setting 
if [ -f /boot/grub/menu.1st ]; then
 grep $IMAGE /boot/grub/menu.1st > /dev/null 2>&1
    if [ "$?" -eq 0 ]; then
 SETTING=1
 fi
fi

# Display the result
if [ "$SPLASHSUPPORT" -eq 0 ]; then
 echo "Splashimage support...NO"
else
 echo "Splashimage support...OK"
 
# also check menu.lst
 if [ $SETTING -eq 1 ]; then
 echo "/boot/grub/menu.1st file has the splashimage setting"
 fi
fi

Calling another boot-loader with "chainloader"

Chainloader command transfers control to another boot-loader. The OSes which use their own boot-loader and don't work with GRUB; can be booted with GRUB's chainloader facility.

Here is the configuration I use to boot WinXP 
title Windows XP 
root (hd0,0) 
makeactive 
chainloader +1
 `+1' is the blocklist notation to point the first sector of the current partition.
makeactive sets the active partition on the root disk to GRUB's root device. This command is limited to primary PC partitions on a hard disk

Virtual swapping of Hard Disk

Windows is happy to see itself on the first partition of the first hard disk. chainloader might not work if windows is on a non first hard disk. This problem can be solved with disk swapping by "map" command. map exchanges BIOS drives virtually. This method makes windows to see as it is on the first sector of first drive 

title Windows 95 
root (hd1,0) 
makeactive
# Here windows has been installed on hd1 
map (hd0) (hd1) 
map (hd1) (hd0) 
chainloader +1

Creating Submenu !!! Yes it is possible :-)

Suppose the submenu file is called submenu.lst and located at /boot/grub
We can call this submenu by placing the configuration below in menu.lst 
# calling submenu 
title Sub-menu 
configfile (hd0,2)/boot/grub/submenu.lst
In submenu.lst file we must have the configuration to come back to the main menu. Below is such an example 
# submenu.lst file
# Go to main menu 
title Main-menu 
configfile (hd0,2)/boot/grub/menu.lst

Hiding GUI

"hiddenmenu" command hides the GUI and boots the default entry after the timeout expired. User can call the GUI by pressing <Esc> before the timeout expires. Add hiddenmenu at the beginning of menu.lst 

# Hide GUI
hiddenmenu

Boot Floppy from GRUB 

# Boot from Floppy
title Boot from Floppy
rootnoverify (fd0)
chainloader +1
boot

Quickly create a PC specific boot floppy with stage1 

# Create Boot Floppy
title Install stage1 into floppy disk
pause Insert a formatted floppy disk and press enter.
root (hd0,2)
setup (fd0)
pause Press enter to continue
Auto creating menu.lst by "update-grub"

debian has update-grub utility which creates menu.lst automatically. The command searches vmlinuz files in /boot and creates the required entries for every found kernels. After update-grub has been run for the first time, the user is required to edit the generated menu.lst to fine tune the configuration.

Resources

GNU GRUB
GNU GRUB FAQ
GNU GRUB Manual 0.97
The list of command line and menu entry commands
GNU GRUB on Wikipedia