GRUB stands for Grand Unified Bootloader. GRUB is the program that is run to start the system, allowing you to select the operating system with which the team is going to start. The window of the GRUB boot loader is shown in Figure 2.4.1.
Figure 2.4.1
In this window, a choice for each of the different existing operating systems on your computer. GRUB configuration is to specify the default operating system to start in the computer and GRUB wait while the selection of other operating systems before they start is indicated by default. In addition, you should select the partition for each operating system and enter a name for each of them. This name is displayed in the window in Figure 2.4.1.
GRUB configuration file is in / boot / grub / menu.lst. The contents of this file might be:
# menu.lst - See: grub (8), info grub, update-grub (8)
# grub-install (8), grub-floppy (8),
# grub-md5-crypt, / usr / share / doc / grub
# and / usr / share / doc / grub-doc /.
# # default num # Set the default entry to the entry number NUM. Numbering starts from 0, and
# the entry number 0 is the default if the command is Not used. # #
Specify Puede 'saved' instead of a number. In this case, the default entry
# is the entry saved with the command 'savedefault'.
# WARNING: If you are using dmraid do not change this entry to 'saved' or your
# array will desync and will not let you boot your system.
default 0
## timeout sec
# Set a timeout, in SEC seconds, before automatically booting the default entry
# (normally the first entry defined).
timeout 10
## hiddenmenu
# Hides the menu by default (press ESC to see the menu)
#hiddenmenu
# Pretty colours
#color cyan/blue white/blue
## password ['--md5'] passwd
# If used in the first section of a menu file, disable all interactive editing
# control (menu entry editor and command-line) and entries protected by the
# command 'lock'
# e.g. password topsecret
# password --md5 $1$gLhU0/$aW78kHK1QfV3P2b2znUoe/
# password topsecret
#
# examples
#
# title Windows 95/98/NT/2000
# root (hd0,0)
# makeactive
# chainloader +1
#
# title Linux
# root (hd0,1)
# kernel /vmlinuz root=/dev/hda2 ro
#
#
# Put static boot stanzas before and/or after AUTOMAGIC KERNEL LIST
### BEGIN AUTOMAGIC KERNELS LIST
## lines between the AUTOMAGIC KERNELS LIST markers will be modified
## by the debian update-grub script except for the default options below
## DO NOT UNCOMMENT THEM, Just edit them to your needs
## ## Start Default Options ##
## default kernel options
## default kernel options for automagic boot options
## If you want special options for specific kernels use kopt_x_y_z
## where x.y.z is kernel version. Minor versions can be omitted.
## e.g. kopt=root=/dev/hda1 ro
## kopt_2_6_8=root=/dev/hdc1 ro
## kopt_2_6_8_2_686=root=/dev/hdc2 ro
# kopt=root=UUID=4b5be2eb-6973-4943-a21f-072809fef4ae ro
## Setup crashdump menu entries
## e.g. crashdump=1
# crashdump=0
## default grub root device
## e.g. groot=(hd0,0)
# groot=(hd0,3)
## should update-grub create alternative automagic boot options
## e.g. alternative=true
## alternative=false
# alternative=true
## should update-grub lock alternative automagic boot options
## e.g. lockalternative=true
## lockalternative=false
# lockalternative=false
## additional options to use with the default boot option, but not with the
## alternatives
## e.g. defoptions=vga=791 resume=/dev/hda5
# defoptions=quiet splash
## should update-grub lock old automagic boot options
## e.g. lockold=false
## lockold=true
# lockold=false
## Xen hypervisor options to use with the default Xen boot option
# xenhopt=
## Xen Linux kernel options to use with the default Xen boot option
# xenkopt=console=tty0
## altoption boot targets option
## multiple altoptions lines are allowed
## e.g. altoptions=(extra menu suffix) extra boot options
## altoptions=(recovery) single
# altoptions=(recovery mode) single
## controls how many kernels should be put into the menu.lst
## only counts the first occurence of a kernel, not the
## alternative kernel options
## e.g. howmany=all
## howmany=7
# howmany=all
## should update-grub create memtest86 boot option
## e.g. memtest86=true
## memtest86=false
# memtest86=true
## should update-grub adjust the value of the default booted system
## can be true or false
# updatedefaultentry=false
## ## End Default Options ##
title Ubuntu, kernel 2.6.20-16-generic
root (hd0,3)
kernel /boot/vmlinuz-2.6.20-16-generic root=UUID=4b5be2eb-6973-4943-a21f-072809fef4ae ro quiet splash
initrd /boot/initrd.img-2.6.20-16-generic
quiet
savedefault
title Ubuntu, kernel 2.6.20-16-generic (recovery mode)
root (hd0,3)
kernel /boot/vmlinuz-2.6.20-16-generic root=UUID=4b5be2eb-6973-4943-a21f-072809fef4ae ro single
initrd /boot/initrd.img-2.6.20-16-generic
title Ubuntu, kernel 2.6.20-15-generic
root (hd0,3)
kernel /boot/vmlinuz-2.6.20-15-generic root=UUID=4b5be2eb-6973-4943-a21f-072809fef4ae ro quiet splash
initrd /boot/initrd.img-2.6.20-15-generic
quiet
savedefault
title Ubuntu, kernel 2.6.20-15-generic (recovery mode)
root (hd0,3)
kernel /boot/vmlinuz-2.6.20-15-generic root=UUID=4b5be2eb-6973-4943-a21f-072809fef4ae ro single
initrd /boot/initrd.img-2.6.20-15-generic
title Ubuntu, memtest86+
root (hd0,3)
kernel /boot/memtest86+.bin
quiet
### END DEBIAN AUTOMAGIC KERNELS LIST
# This is a divider, added to separate the menu items below from the Debian
# ones.
title Other operating systems:
root
# This entry automatically added by the Debian installer for a non-linux OS
# on /dev/hda1
title Microsoft Windows XP Professional
root (hd0,0)
savedefault
makeactive
chainloader +1
######## ###### END OF FILE
active information (these are the lines that are not mentioned) in this file is: default
line indicates the partition that starts by default if the time specified in timeout, the user does not select another partition. The value 0 refers to the first label title that appears in / boot / grub / menu.lst, the value 1 refers to the second title tag appears in the / boot / grub / menu.lst, and so on.
timeout line indicates how many seconds the system waits to start the default operating system.
The lines are below the line # # # # End Default Options # #, indicates the hard disk and partition are each operating system that can be started in the system.
quiet splash parameters are used during system startup display a graphical environment. If we take these arguments, the startup is displayed in text mode.
In the / boot / grub / menu.lst, you can set passwords to start each of the operating systems installed on the system. To do this, add the password password line in paragraphs title that define each of the partitions system.
The file / boot / grub / menu.lst you can install by running the command grub-install / dev / sda. The device / dev / sda shows the hard drive where we want to install. This command performs a compilation of the file, if no errors, it installs in the Master Boot Record (MBR) of hard disk indicated.
The file / boot / grub / menu.lst, you can create or modify the order by running update-grub. This command looks for kernel versions located in the / boot directory and creates an entry in / boot / grub / menu.lst for each of these versions. A possible way out of the execution of this order would be: root @
alsico-laptop: ~ # update-grub
Searching for GRUB installation directory ... found: / boot / grub
Testing for an existing GRUB menu.lst file ... found: / boot / grub / menu.lst Searching for splash
image ... none found, skipping ...
Found kernel: / boot/vmlinuz-2.6.20-16-generic Found
kernel: / boot/vmlinuz-2.6.20-15-generic Found kernel
: / boot/memtest86 +.
bin Updating / boot / grub / menu.lst ...
actually done, GRUB is a framework from which you can perform various operations, entering commands specific to the environment. To start this environment, you must press the C key on the window in Figure 2.4.1 or, once started the system, run the command grub. It shows the prompt grub>, from which you can write GRUB orders. From this environment comes typing reboot, if we have agreed to the environment from the startup menu, or quit writing if we accessed the environment once the system.
From the window in Figure 2.4.1, lines can also edit the file / boot / grub / menu.lst to change their values \u200b\u200band start the system with the new values \u200b\u200bentered. To do so, press the button and the window in Figure 2.4.1.
password password line if we write out of the blocks which define the operating systems on startup window is shown in Figure 2.4.2.
Figure 2.4.2
As we see in this window, you can not access the commands to enter the GRUB environment. To enter this environment, you must press the enter key, eg, in the new window, the password specified in / boot / grub / menu.lst.
If you entered the command lock in a title block in the file / boot / grub / menu.lst and assigned a password out of the blocks to disable the entry in the GRUB environment at startup (window in Figure 2.4.2), we have to press the p-type the password to boot from the partition on which the order has been included lock.
These passwords are visible to consult the file / boot / grub / menu.lst (this file can be read by any user) or by editing the startup option in the boot menu of the window in Figure 2.4.1 (by pressing and with the boot option selected). For the password is not legible, we encrypt it, To do this, you have to access the environment from the GRUB command line by running the command grub. In this environment, execute the order md5crypt and write the password to encrypt. The environment gives us back the encrypted password with the message Encrypted: $ 1 $ biPFG $ wjeFI4XkAPpM6Clio6iZA1. This password must be copied to add the file / boot / grub / menu.lst. Exit the GRUB environment by running the command quit.
Then edit / boot / grub / menu.lst and insert the following line:
password - md5 $ 1 $ biPFG $ wjeFI4XkAPpM6Clio6iZA1 (this is the encrypted password that we copied from the GRUB environment).
When prompted for a password when the system must write the unencrypted password.
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