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To rewrite Grub
To only re-write grub to MBR from the hard drive, ie due to a newer grub-version:
/usr/sbin/grub-install --recheck --no-floppy /dev/sda
This line may need to be run more than once, until its convinced you really mean it.
Bootsector overwritten by Windows MBR and /or to recover grub
To rewrite the grub to the MBR and/or to recover grub in general, you will need boot up a sidux live-cd, first:
- To identify and confirm your partitions (e.g. [h,s]d[a..]X) all the following actions need root privileges, so to get root (#):
$ sux
- When in root type in:
fdisk -l cat /etc/fstab
This is to get the correct names. - When you have acertained the correct partition, create the mount point:
mkdir -p /media/[hdxx,sdxx,diskx]
- Mount it:
mount /dev/xdxx /media/xdxx
- Now rewrite Grub to MBR of the first harddisk (generic):
/usr/sbin/grub-install --recheck --no-floppy --root-directory=/media/xdxx /dev/sda
Example
root@sidux:/home/sidux# fdisk -l # fdisk -l Disk /dev/sda: 115.9 GB, 115989736960 bytes 255 heads, 63 sectors/track, 14101 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0x40444044 Device Boot Start End Blocks Id System /dev/sda1 * 1 3673 29503341 7 HPFS/NTFS /dev/sda2 3674 14101 83762910 5 Extended /dev/sda5 3674 7239 28641784+ 83 Linux /dev/sda6 7239 10842 28934104+ 83 Linux /dev/sda7 10843 14101 26177886 b W95 FAT32 Disk /dev/sdb: 120.0 GB, 120034123776 bytes 255 heads, 63 sectors/track, 14593 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0xa41e667f Device Boot Start End Blocks Id System /dev/sdb1 1 3574 28708123+ 83 Linux /dev/sdb2 3575 7247 29503372+ 83 Linux /dev/sdb3 7248 10845 28900935 83 Linux /dev/sdb4 10846 14593 30105810 5 Extended /dev/sdb5 * 10846 14338 28057491 83 Linux /dev/sdb6 14339 14593 2048256 82 Linux swap / Solaris Disk /dev/sdc: 250.0 GB, 250059350016 bytes 255 heads, 63 sectors/track, 30401 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0x00077541 Device Boot Start End Blocks Id System /dev/sdc1 1 30401 244196001 83 Linux Disk /dev/sdd: 250.0 GB, 250059350016 bytes 255 heads, 63 sectors/track, 30401 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0x1c01ad92 Device Boot Start End Blocks Id System /dev/sdd1 1 30401 244196001 83 Linux root@sidux:/home/sidux# cat /etc/fstab # /etc/fstab - static information about the filesystems - fstab(5) # # /etc/fstab is only read by programs, and not written; it is the duty of the # system administrator to properly maintain this file. # # Instead of giving the device explicitly, one may indicate the filesystem # that is to be mounted by its UUID or VOLUME label. This will make the # system more robust: adding or removing a disk changes the disk device name # but not the filesystem UUID or VOLUME label. # automatically added, ST3120026A-3LJ093B4-part1 /dev/sda1 /media/disk0 ntfs noauto,users,exec,ro,dmask=0022,fmask=0133 0 0 # automatically added, ST3120026A-3LJ093B4-part5 /dev/sda5 /media/disk1 jfs noauto,users,exec,noatime 0 2 # automatically added, ST3120026A-3LJ093B4-part6 /dev/sda6 /media/disk2 reiserfs noauto,users,exec,noatime 0 2 # automatically added, ST3120026A-3LJ093B4-part7 /dev/sda7 /media/disk3 vfat noauto,users,exec,shortname=lower,quiet,umask=000 0 0 # automatically added, ST3120026A-3LJ09RBF-part1 /dev/sdb1 /media/disk4 reiserfs noauto,users,exec,noatime 0 2 # automatically added, ST3120026A-3LJ09RBF-part2 /dev/sdb2 /media/disk5 ext3 noauto,users,exec,noatime 0 2 # automatically added, ST3120026A-3LJ09RBF-part3 /dev/sdb3 /media/disk6 reiserfs noauto,users,exec,noatime 0 2 # automatically added, ST3120026A-3LJ09RBF-part5 /dev/sdb5 /media/disk7 ext3 noauto,users,exec,noatime 0 2 # automatically added, ST3120026A-3LJ09RBF-part6 /dev/sdb6 none swap sw 0 0 # automatically added, ST3250824AS-4ND1V199-part1 /dev/sdc1 /media/disk9 ext3 noauto,users,exec,noatime 0 2 # automatically added, ST3250620AS-9QE13XVF-part1 /dev/sdd1 /media/disk10 ext3 noauto,users,exec,noatime 0 2 # automatically added, _NEC_DVD_RW_ND-4550A /dev/cdrom /media/cdrom udf,iso9660 user,noauto 0 0 # automatically added, ASUS_DVD-ROM_DVD-E616P_0104 /dev/cdrom1 /media/cdrom1 udf,iso9660 user,noauto 0 0 # automatically added /dev/fd0 /media/fd0 auto rw,user,noauto 0 0 # temporary filesystem in virtual memory #tmpfs /tmp tmpfs defaults 0 0
root partition is /dev/sdb1 and your MBR goes on sda mkdir -p /media/sdb1 mount /dev/sdb1 /media/sdb1 /usr/sbin/grub-install --recheck --no-floppy --root-directory=/media/sdb1 /dev/sda
On older linux systems, the IDE disks devices (PATA) were differentiated from those using current standard by an hdaX name instead of sdaX
Creating a bootable Floppy
To make yourself a boot floppy, use the tools provided in UBCD (Ultimate Boot Disk CD)
Removing grub from MBR
It's very simple: as root enter
lilo -M /dev/hda -s /dev/null
in a terminal.
GRUB the Boot Manager - what it is
General
NOTE Grub for kernels 2.6.22 and up uses sdax
and the line
initrd (hd0.x)/sidux/miniroot.gz
has changed to:
initrd /boot/initrd.img-2.6.xx.x-slh-smp-x
Grub is a boot manager that can boot operating systems from different partitions. Grub does not rely on block lists to find the needed files for a system to start up, and it can read a bunch of file-systems by default: ext2, ext3, reiserfs, ... (Linux), Fat32, Fat16 (Windows), UFS (BSD), Minix and many others.
Grub knows BIOS-extensions (meaning it can boot partitions above 8 GByte!) and has no 1024-cylinder-barrier. Grub doesn't really care, where the kernel physically resides, all it needs is the declaration of the partition and the path to the kernel it's supposed to boot (this can even be a symlink). After a change in the configuration (i.e. the menu.lst) it doesn't need a program-call like Lilo does, the new configuration is applied at next boot.
sidux uses Grub to boot from CD, and when installing to harddisk, Grub is used by default. Nonetheless Grub can be installed afterwards without a problem. Grub is installed to the MBR from a root-shell with the following command:
grub-install --root-directory=/media/hdaX /dev/hdY
/media/hdaX stands for the readable-mounted partition, on which, in the directory "/boot/grub" the necessary files (stage2, stage1_5xxx) will be placed. The configuration file "menu.lst" must also be created in that directory. /dev/hdY is the harddisk, in whose MBR Grub will be installed, normally /dev/hda.
Drivenames/Devicenames
Please Note: hda is in the process of being depreciated, therefore you need to start substituting hda with sda for kernels 2.6.22 and onward.
Grub does not differentiate between SCSI- and IDE-Harddisks. (hd0) is always the first hard disk that is first in the boot sequence (setting in BIOS), no matter if IDE or SCSI. Unusual is the counting method; the first partition on the first hd is (hd0,0). Primary partitions are numbered from 0-3, logical partitions count from 4 on up.
| Grub | Linux | Label |
|---|---|---|
| (fd0) | /dev/fd0 | Floppy (under Windows) |
| (hda0) | /dev/hda | first hd |
| (hd0,0) | /dev/hda1 | Part.1 on hd1 |
| (hd0,5) | /dev/hda6 | Extended. part. on hd 1 |
All nominations for devices for Grub are to be put in brackets (). Be aware of the entries behind the Kernel-line though. In contrast to Grub the Kernel needs the data in the normal linux way. The entries in the following example both point to the same partition, namely the fourth partition on the first hd. The first line is in Grub notation, the second one in typical linux notation:
root (hd0,3) kernel /boot/vmlinuz root=UUID=bf955abf-ce1f-45a3-9ee5-93b5c5dc4fe0 ro quiet vga=791 initrd /boot/initrd.img
Command-Mode (Grub-Shell)
A very comfortable feature is the Command-Mode. It is accessed by "c", and here comes the Grub-Shell. This enables you to find and boot different systems and files (i.e. Kernel) even with a faulty menu.lst.
To do a little bit of testing, you can even run Grub from a booted system from within a root-shell with "grub". In the Grub-Shell you can see all possible commands with "help". Detailed help for each command is obtained with help command", back to the Linux-Shell you go with "quit"( Grub-Shell is terminated). In the Grub-Shell the tab-key has a similar function as in the Linux-Shell, which is a great ease. Commands, Drivenames and Filenames can be auto-completed with the tab-key.
Grub gives you the opportunity to locate the Kernel and the initrd even before the actual boot by "find" , e.g.with the following command
find /boot/vmlinuz
Grub shows the partitions, that have a Kernel with the name "vmlinuz" in the directory "/boot":
(hd0,3) (hd1,0)
All available partitions can be found with "geometry", e.g.
geometry (hd0)
shows this:
"drive 0x80: C/H/S = 3648/255/63, The number of sectors = 58605120, /dev/hda Partition num: 0, Filesystem type is fat, partition type 0xb Partition num: 1, Filesystem type is fat, partition type 0xb Partition num: 2, Filesystem type is fat, partition type 0xc Partition num: 4, Filesystem type is ext2fs, partition type 0x83 Partition num: 5, Filesystem type unknown, partition type 0x82 Partition num: 6, Filesystem type is fat, partition type 0xb"
After the Kernel or an existing initrd (or miniroot.gz) has been found, you can start with "boot".
Edit-Mode
This mode enables you to change entries in the "menu.lst" while booting. This works even when Grub is booted from CD and the menu.lst is write-protected . To do so you first hit ESC, confirm with Return and then hit "e". The parameters are then added to the end of the line or you move within the line with the Cursor-keys.
menu.lst (examples for possible entries)
Lines with comments are started with # and don't interfere with the bootprocess, so they can stay in the file.
# Example /boot/grub/menu.lst ################################################ # setkey changes the keyboardlayout to german (as an example) setkey y z setkey z y setkey Y Z setkey Z Y setkey equal parenright setkey parenright parenleft setkey parenleft asterisk setkey doublequote at setkey plus bracketright setkey minus slash setkey slash ampersand setkey ampersand percent setkey percent caret setkey underscore question setkey question underscore setkey semicolon less setkey less numbersign setkey numbersign backslash setkey colon greater setkey greater bar setkey asterisk braceright # 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. default 0 ## timeout sec # Set a timeout, in SEC seconds, before automatically booting the default entry # (normally the first entry defined). timeout 5 # Pretty colours color cyan/blue white/blue gfxmenu (hd0,5)/boot/message ## 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=1885d68b-cc9c-49f8-9f98-a6874e7b3e7e ro quiet vga=791 ## default grub root device ## e.g. groot=(hd0,0) # groot=(hd0,5) ## should update-grub create alternative automagic boot options ## e.g. alternative=true ## alternative=false # alternative=false ## 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= ## 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=(single-user) single # altoptions=(single-user 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 Debian GNU/Linux, kernel 2.6.22.1-slh-smp-7 root (hd0,5) kernel /boot/vmlinuz-2.6.22.1-slh-smp-7 root=UUID=1885d68b-cc9c-49f8-9f98-a6874e7b3e7e ro quiet vga=791 initrd /boot/initrd.img-2.6.22.1-slh-smp-7 title Debian GNU/Linux, kernel 2.6.22.1-slh-smp-7 (single-user mode) root (hd0,5) kernel /boot/vmlinuz-2.6.22.1-slh-smp-7 root=UUID=1885d68b-cc9c-49f8-9f98-a6874e7b3e7e ro quiet vga=791 single initrd /boot/initrd.img-2.6.22.1-slh-smp-7 ### END DEBIAN AUTOMAGIC KERNELS LIST #### MS (TM) title Windows 2K/XP/2003 (hda1) chainloader (hd0,0)+1 ### ISO boot title sidux 32bit from gaiaISO kernel (hd0,3)/sidux3/vmlinuz-2.6.22.1-slh-smp-7 boot=fll quiet vga=791 fromiso=/sidux3/siduxgaia.iso initrd (hd0,3)/sidux3/initrd.img-2.6.22.1-slh-smp-7 title Debian GNU/Linux, kernel 2.6.18-1-686 (hda5) root (hd0,4) kernel (hd0,4)/boot/vmlinuz-2.6.18-1-686 root=/dev/hda5 ro vga=791 initrd (hd0,4)/boot/initrd.img-2.6.18-1-686 savedefault
Dual and Multiple Booting
NOTE Grub for kernels 2.6.22 and up uses sdax
and the line
initrd (hd0,x)/sidux/miniroot.gz
has changed to:
initrd /boot/initrd.img-2.6.xx.x-slh-smp-x
To enable multiple grub OS booting is very simple with the use of chainloading. If for example you want to run a MS Windows (TM) and Debian etch OS along with a sidux 'fromiso' installation , you will need to customise grub a bit, Therefore edit the file /boot/grub/menu.lst and add the following lines after the ### END DEBIAN AUTOMAGIC KERNELS LIST:
####MS Windows (TM) perhaps even MS Vista (TM) Title Windows (95/98/XP/Vista rootnoverify (hd0,1) makeactive chainloader +1 ### Debian etch title Debian etch kernel (hd0,3)/debian/vmlinuz root=/dev/hda4 ro (or whatever) initrd (hd0,3)/debian/miniroot.gz (or (whatever) ### ISO boot title sidux 32bit from gaiaISO kernel (hd0,3)/sidux3/vmlinuz-2.6.22.1-slh-smp-7 boot=fll quiet vga=791 fromiso=/sidux3/siduxgaia.iso initrd (hd0,3)/sidux3/initrd.img-2.6.22.1-slh-smp-7
Some people need/want several MS Windows (TM)Installations. MS Windows (TM) always wants to boot from disk 1. We will have to hide one partition and activate another. The following commands should be entered in the GRUB-Commandline and, if successfull, copied to the menu.lst. This should be done for every Windows-partition. Don't forget to do a Backup:
hide (hd0,0) # hidden partition 1 of disk 1 unhide (hd0,1) # makes partition 2 of disk 1 visible rootnoverify (hd0,1) # makes partition 2 of disk 1 the Root-FS makeactive # makes partition 2 of disk 1 active chainloader +1 # points to the first sector of the start-partition boot # boots the operating system
If you want to start a 2nd Windows from the 2nd disk, you virtually swap disk 1 and 2. Thereby Windows sees a simulated 1st disk:
map (hd0) (hd1) map (hd1) (hd0)
Pitfalls
As Grub has no 1024-cylinder barrier and can boot systems above 1024 cylinders, the "/boot/grub/stage2" must be accessible by the bios (must be before 1024 cylinders). Stage2 may not be moved after installation (e.g. Defrag could try that). Setup data will get written that would not be congruent anymore. It is reasonable to make stage2 read-only (you must be in the current directory):
Dos: attrib +r +s stage2 LINUX: # chmod a -w ./stage2
Where to find out more
If you have a supported network card, Grub can boot over the network. An appropriate Boot-Disk can be obtained here (allthough with an older version of Grub).