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Old 09-22-2006, 01:20 PM   #1
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Need help identifying the lines of Grub.conf file

I am new to Linux and need some help! Would someone pllease explain what each line of the grub.conf file means, and what the initrd is? Thanks for any help, Sarge_P
Old 09-22-2006, 01:24 PM   #2
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Originally Posted by Sarge_P
I am new to Linux and need some help! Would someone pllease explain what each line of the grub.conf file means, and what the initrd is? Thanks for any help, Sarge_P
That's a very broad question. Sorry my friend but that's what google search/documentation is for. Once you have done search and read up on it, you can post specific questions here.

BTW, welcome to LQ

Old 09-22-2006, 03:40 PM   #3
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Rep: Reputation: 351Reputation: 351Reputation: 351Reputation: 351 is your friend. is for general search, add the /linux for Linux related searches. Sifts out the dross and flotsam, don't you know.
Old 09-22-2006, 04:04 PM   #4
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Actually it is a simple question so may be a simple answer will suffice.

With a menu Grub boots every system by

(1) A title statement to tell the name of the system. Anything after "title" has no consequence.

(2) A root statement to identify the root partition of the system. Grub count from 0 and so (hd0) means 1st disk and its 7th partition is known as (hd0,6)

(3) A kernel statement to load the kernel at the location immediatel after "kernel". There may be parameters needed to passed to the kernel and these are supplied after the kernel location

(4) A initrd statement to load the ramdisk file at the location immediately after "initrd". This statement is optional and many distros do not use it, e.g. all Slackware and Slax families.

Grub can also boot a system by chainloading. This is necessary if the OS has no formal kernal like the XP. In such a case Grub simply boots its boot loader. It still needs the Item (1) & (2) but in place of Item (3) & (4) a general statement
chainloader +1
is all that is required.

The +1 position means Grub will keep its 1st sector (MBR) and paste itself with boot loader found in the "root" staement starting from the 2nd sector onward.

Sorry for the long wind answer but it is actually very simple and works for any Dos, Windows, Linux and PC-based Unix system.

Last edited by saikee; 09-22-2006 at 04:05 PM.
Old 09-22-2006, 04:09 PM   #5
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Originally Posted by Sarge_P
I am new to Linux and need some help! Would someone pllease explain what each line of the grub.conf file means, and what the initrd is? Thanks for any help, Sarge_P
>$ cat /boot/grub/menu.lst
# 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.
# You can specify 'saved' instead of a number. In this case, the default entry
# is the entry saved with the command 'savedefault'.
default         0
The default line does what the comments say the 0 (zero which is what grub starts counting with instead of 1) tells it to boot the first entry of the menu image configuration and save here boots the last used option if the section for it contained the savedefault in it.
## timeout sec
# Set a timeout, in SEC seconds, before automatically booting the default entry
# (normally the first entry defined).
timeout         5
How long to wait before booting the default image.
# Pretty colours
color cyan/blue white/blue
Customize colours of boot splash screen.

## 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
Using password to protect the boot options.
# examples
# title         Windows 95/98/NT/2000
# root          (hd0,0)
# makeactive
# chainloader   +1
# title         Linux
# root          (hd0,1)
# kernel        /vmlinuz root=/dev/hda2 ro
Examples to help you configure your own entries.

# Put static boot stanzas before and/or after AUTOMAGIC KERNEL 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=/dev/sda2 ro
The kopt= tells update-grub where your root file system is located for menu entry additions.

## default grub root device
## e.g. groot=(hd0,0)
# groot=(hd0,1)
This tells update-grub where the grub root device is located in its terms for example my /dev/sda2 above gets translated to hd0 first hard drive in system ,1 second partition.

## should update-grub create alternative automagic boot options
## e.g. alternative=true
##      alternative=false
# alternative=true
Exactly what it says should grub make alternative boot entries other than a main menu entry.

## should update-grub lock alternative automagic boot options
## e.g. lockalternative=true
##      lockalternative=false
# lockalternative=false
Should the entry be locked.

## additional options to use with the default boot option, but not with the
## alternatives
## e.g. defoptions=vga=791 resume=/dev/hda5
# defoptions=
Extra options to add to main boot menu entries.

## should update-grub lock old automagic boot options
## e.g. lockold=false
##      lockold=true
# lockold=false
Lock the old entries when updating to new.

## Xen hypervisor options to use with the default Xen boot option
# xenhopt=
Options when using Xen to boot.

## Xen Linux kernel options to use with the default Xen boot option
# xenkopt=console=tty0
More Xen options.

## altoption boot targets option
## multiple altoptions lines are allowed
## e.g. altoptions=(extra menu suffix) extra boot options
##      altoptions=(single-user) single
# altoptions=(recovery mode) single
The options to add when making the alternative boot menu entries.

## 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
How many kernel you want to be able to boot from the menu.

## should update-grub create memtest86 boot option
## e.g. memtest86=true
##      memtest86=false
# memtest86=true
Create memtest86 entry if the program is installed so you can test your ram.

## should update-grub adjust the value of the default booted system
## can be true or false
# updatedefaultentry=false
Not sure.

## ## End Default Options ##

title           Debian GNU/Linux, kernel 2.6.18-ck1-smp Default
root            (hd0,1)
kernel          /boot/vmlinuz root=/dev/sda2 ro
A menu entry for boot the title part is what is displayed on the menu, the root is the location of the root partition that grub will boot, the kernel line is the location of the kernel image that will be booted and savedefault tells grub that this will be the default option when booting next time if specified to do so above in default save instead of using number (0) entry.
title           Debian GNU/Linux, kernel 2.6.18-ck1-smp Default (recovery mode)
root            (hd0,1)
kernel          /boot/vmlinuz root=/dev/sda2 ro single
Example of the alternative entry created with the options specified in the # altoptions=(recovery mode) single configuration item.

title           Debian GNU/Linux, kernel 2.6.17-ck1-1-smp Previous
root            (hd0,1)
kernel          /boot/vmlinuz.old root=/dev/sda2 ro
initrd          /boot/initrd.img.old

title           Debian GNU/Linux, kernel 2.6.17-ck1-1-smp Previous (recovery mode)
root            (hd0,1)
kernel          /boot/vmlinuz.old root=/dev/sda2 ro single
initrd          /boot/initrd.img.old
Examples of the previous installed kernel.

title           Debian GNU/Linux, kernel 2.6.8-11-amd64-generic
root            (hd0,1)
kernel          /boot/vmlinuz-2.6.8-11-amd64-generic root=/dev/sda2 ro
initrd          /boot/initrd.img-2.6.8-11-amd64-generic

title           Debian GNU/Linux, kernel 2.6.8-11-amd64-generic (recovery mode)
root            (hd0,1)
kernel          /boot/vmlinuz-2.6.8-11-amd64-generic root=/dev/sda2 ro single
initrd          /boot/initrd.img-2.6.8-11-amd64-generic
Original install kernel which shows the use of an initrd line when using that type of kernel.


# This is a divider, added to separate the menu items below from the Debian
# ones.
title           Other operating systems:

# This entry automatically added by the Debian installer for a non-linux OS
# on /dev/hda1
title           Microsoft Windows XP Professional
root            (hd0,0)
chainloader     +1
Example of menu item to boot windows on the first (hd0) hard drive first partition (0).
Old 09-25-2006, 01:03 PM   #6
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Thumbs up Linux Grub.conf.

Thank you to the postings. They helped me greatly. Have a good day.


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