Bootloader / multi-boot
Bootloaders
• Grand Unified Bootloader (GRUB)
• Linux Load (LILO)
GRUB
• Discovers boot images, kernels, and root
filesystems from GRUB command shell
• Stores boot info in a filesystems (not the
MBR)
• Reads filesystems and kernel executables
– Does not restrict user to disk geometry
• OS independent
– Store GRUB in a separate boot partition
• Remove and reinstall OS’s w/o having to reinstall the
bootloader
GRUB and LILO
• Can boot non-Linux systems
– Windows, OS/2, BSD, etc
• Chain loading
– Points to OS’s bootloader (ie, Windows)
MBR
• First 512 bytes of the first sector of the
first partition on a drive
– Contains partition table and 1st stage
bootloader
• 1st stage is first 445 bytes
– Point to 2nd stage loader
» Stored in /boot directory
• Remaining 66 bytes
– Partition table
Linux
• Limited to 63 total partitions per IDE
drive
– 3 primary
– 4th: contains up to 60 logical partitions in a
single extended partition
• SCSI drives
– Limited to 15 partitions
• 3 primaries
• 12 logicals
Scenario
• LILO installed, you wish to install GRUB
– Determine the version of grub
$grub –version
grub (GNU GRUB 0.94)
– Hard copy your partition table
fdisk –l | lpr
– Hard copy lilo.conf
– Back up data
– Keep rescue disk handy
• LILO boot or Knoppix
– Leave LILO intact… in case
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Create GRUB boot diskette
Install GRUB to MBR
Boot the system
Edit GRUB configuration file
– menu.lst
Scenario
•
Create GRUB boot diskette
/grub/i386-pc (can vary)
could be in /usr/lib or /usr/share or…
– Copy stage1 and stage2 to diskette with dd command
$ dd if=stage1 of=/dev/fd0 bs=512 count=1
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Reboot the system (you get the GRUB screen)
Find the root device
grub> find /boot/grub/stage1
(hd0,0)
•
Set the root device
grub> root (hd0,0)
•
Install GRUB to MBR
grub> setup (hd0)
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Set the root device (again)
•
grub> root (hd0,0)
Enter the path to the kernel and the root filesystem (in lilo.conf)
–
MAKE SURE YOU APPEND “ro” (read only)
grub> kernel /boot/vmlinuz-2.4.21 root=/dev/hda1 ro
•
Now, boot the system
grub> boot
Gotchas
• Linux refers to drives as hd1, hd2, etc…
• GRUB starts with “0” (h0, h1, etc)
– Both SCSI and IDEs are hd, floppies are fd
• Linux primary partitions
• 1-4
• 5 and up.. Extended partitions
• GRUB
• 0-3
• 4 and up
primary
extended
• Identifying the root filesystem does not use
GRUB’s numbering sytem
grub> kernel /boot/vmlinuz-2.4.21 root=/dev/hda1 ro
Install GRUB w/o floppy
• Start a grub shell
# grub
• Find the stage1 loader
grub> find /boot/grub/stage1
(hd0,0)
• Run
grub> root (hd0,0)
grub> setup (hd0)
grub> quit
• Reboot
Multi-booting Linux
• Standalone /boot partition
• Shared /home and /swap partitions
• Standard Fedora install (on 20Gb IDE)
– /dev/hda1
– /dev/hda2
– /dev/hda3
– /dev/hda4
– /dev/hda5
– Free space
primary
primary
primary
extended
100Mb
2,500Mb
3,000Mb
/boot
/
/home
256Mb
14,144
/swap
Disk Druid
• Used to partition
• Delete any existing partitions
• Highlight ‘free space’
– Click ‘new’
• Mountpoint is /boot
ext2, 100Mb
• Select ‘free space’ again
– ‘new’
• Mountpoint is “/”
ext3, 2500Mb
– Next
• /home
• Find “swap”
ext3, 3000Mb
no mountpoint, 256Mb
• When done, save changes using Disk Druid
• Continue install, using GRUB (not LILO)
QTPared
• Create, delete, move and resize partitions
– Included on Knoppix
• Can be used to set up partitions even before new Linux
install
• Can be used to make changes to partitions even if data
on them
• /swap
– Performance issues, put in its own partition
• Shared on multiboot system
• /home
– Own partition
• Share between different Linux systems
• Not forced to restore data from backup when installing or
removing systems
Adding another Linux
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Add additional Linux systems into logical partitions
Create a GRUB boot menu entry for each
After 1st Linux installed
– Boot install of the new Linux
– Partition and drive layouts
• Highlight “free” and select “new”
– 2500Mb for size (mountpoint is “/”)
» Select filesystem type and initialize it (/dev/hda6)
• Select /dev/hda3 to “Modify”
– Select /home and ext3, do not initialize it
– When done, write the partition info to disk
• When prompted, you should only be formatting or initialing the “/” partition
– Do NOT overwrite the MBR
• Do you want Linux to handle booting system? “NO”
– You want boot files installed to first sector of the root partition (/dev/hda6)
• Use GRUB
grub> root (hd0,0)
grub> kernel / boot/vmlinuz-2,4,21 root=/dev/hda6 ro
grub> boot
Finding the boot parameters
using GRUB
• As grub is booting up, hit “c”
– Get to the GRUB command shell
grub>root (hd0, <tab>
[tab completion]
• possible partitions identifies along with filesystem type
and partition type
– Try them if needed…
grub> root (hd0,0)
• Search for kernel image
grub> kernel /boot/vmlinuz<tab>
» May report file not found
grub> root (hd0,1)
grub> kernel /boot/vmlinuz<tab>
possible files are: vmlinuz vmlinuz-2.4.2
grub> kernel / boot/vmlinuz-2,4,21 root=/dev/hda2 ro
grub> boot
Miscellaneous
• grub> cat /etc/shadow
• grub> root(hd<tab>
– Possible disks are: hd0 hd1
• Grub can be password protected
• Documentation
www.gnu.org/software/grub/manual/grub.html
GRUB boot menu
• /boot/grub/menu.lst
• “stanza”
– GRUB boot entry
title
root
kernel
initrd
Fedora 1 core
(hd0,0)
/boot/vmlinuz-2.4.22-1 root=/dev/hda1 ro
/boot/initrd-2.4.22-1.img
• Title: required, can be anything
• Each OS requires a stanza entry
• Initrd: ramdisk (not all Linux implementations
require a ramdisk)
GRUB boot menu
• menu.lst (or grub.conf)
• Default entry
– Number of the stanza (sequential)
• Timeout entry
– How long to wait for default entry to boot
• splashimage
• defaultsaved
– Last image used to boot is saved as the
next default
Adding Windows to a Linux
system
• Different considerations for 95 thru ME as opposed to
NT/2000/XP
• XP
– Make sure there’s enough free space and unused primary partition
– Hard copy the partition table
• Note what’s installed on each partition
– Install from CD
• Install complete
– Restore the GRUB to the MBR
• Load GRUB boot floppy
grub> root (hd0,0)
grub> setup (hd0)
grub> reboot
• Boot to Linux, and make an entry for the Windows system
title
WindowsXP on /dev/hda4
rootnoverify
(hd0,3)
makeactive
chainloader +1
Restore GRUB to MBR w/Knoppix
•
If installation of Windows overwrote
the MBR and GRUB with the Windows
Boot Menu you can no longer boot to
Linux
– Boot the Knoppix CD
– su to root and run GRUB
– Put GRUB onto the MBR
grub> Root (hd0,0)
grub> setup (hd0)
grub> quit
– Reboot and GRUB menu appears
Password protecting GRUB
# grub-md5-crypt
• Copy and paste the encrypted password into
menu.lst before the boot stanzas
password –md5 $1$riAfJ0$QTuA1S/BGqlkYHQADZejs1
Or… plaintext password can be used…
password mypasswordisthis
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Chmod the menu.lst file if needed (root only)
When booting GRUB, hit “p” and enter the password to unlock the
command shell
– Users can still select.. Just can use command shell
•
(**** if you forget the GRUB password, anyone can simply boot
with rescue disk and edit menu.lst *****)
Assignment:
• Install Red Hat on box w/GRUB
• Install Mandriva as second Linux
• Install Windows XP as third system