GRUB: GRand Unified Bootloader
The GRUB bootloader is first run when the computer initially boots. After it runs, it passes control to the operating system kernel. GRUB is typically installed on the MBR of the hard drive but can also be installed on a floppy to rescue the system if the MBR is overwritten or corrupted.
Note: Grub "Legacy" refers to the 0.9x versions of Grub.
- Grub 0.95 (Red Hat Enterprise 4, Fedora Core 3, CentOS4) is configured with /etc/grub.conf (soft link to /boot/grub/grub.conf or /boot/grub/menu.1st)
- Grub 0.97 (Ubuntu 6.11) is configured with a multiple configuration files including:
- /boot/grub/menu.lst: Typical Grub directives (was grub.conf)
- /boot/grub/device.map: List devices e.g. (hd0) /dev/sda
- /boot/grub/default: Set with the command "grub-set-default". Typical value is "0" to boot the first kernel listed. Example: grub-set-default 0
- /boot/grub/stage1: Embedded in MBR (boot sector partition) thus is 512 bytes. Encodes location of stage 2.
- /boot/grub/stage2: Put on a filesystem, this is the core image of GRUB.
GRUB is an operating system independant boot loader and shell. GRUB uses a device naming system which is different and independant of the one used by Linux. For example (hd0,0), the designation "hd0" refers to the first hard drive. The second designation refers the the partition number. Each begin counting from "0". Some systems like BSD may include more designations. Note that GRUB does not distinguish EIDE from SCSI.
|Linux device name||GRUB name||Linux filesystem
Sample config file: /etc/grub.conf (Linked to actual file: /boot/grub/grub.conf).
default=0 timeout=10 splashimage=(hd1,0)/grub/splash.xpm.gz - Image to be displayed: /boot/grub/splash.xpm.gz which is on the 2nd hard drive, 1st partition. title Red Hat Linux (2.4.9-21) root (hd1,0) - Root of GRUB reference. Same as /boot. See above table. kernel /vmlinuz-2.4.9-21 ro root=/dev/sdb6 - Note that the command cat /proc/cmdline should be the same as "ro root=/dev/sdb6" initrd /initrd-2.4.9-21.img - Referenced from GRUB root reference. Hence file: /boot/initrd-2.4.9-21.img
Create GRUB boot floppy:
[root prompt]# fdformat /dev/fd0H1440 [root prompt]# mke2fs /dev/fd0 [root prompt]# mount -t ext2 /dev/fd0 /mnt/floppy [root prompt]# grub-install --root-directory=/mnt/floppy '(fd0)' [root prompt]# cp /boot/grub/grub.conf /mnt/floppy/boot/grub/grub.conf [root prompt]# umount /mnt/floppy
The small reduced kernel /boot/vmlinuz-...BOOT and support files in /boot can be loaded on the floppy to create other boot options.
Method 1:Creating a GRUB boot floppy:
- cd /lib/grub/i386-pc
- dd if=stage1 of=/dev/fd0 bs=512 count=1
- dd if=stage2 of=/dev/fd0 bs=512 seek=1
This will write files stage1 and stage2 to the first and second block of the floppy disk.
- mke2fs /dev/fd0
- mount -t ext2 /dev/fd0 /mnt/floppy
- grub-install --root-directory=/mnt/floppy fd0
- umount /mnt/floppy
Lilo is the "Boot Loader" for Linux which typically resides on the MBR of your hard drive. This may easily get wiped out on a multiboot system where a re-loading of the Windows operating system will reload the MBR. If the MBR is overwritten and LILO removed, there will be no way of booting to Linux. Thus it is wise to have a floppy with LILO residing on the MBR of the floppy which can point the system to boot off of the Linux kernel residing on your hard drive. Here is how it is created:
- fdformat /dev/fd0H1440 # Lay tracks on new diskette
- mkfs -t minix /dev/fd0 1440 # Create minix file system on floppy
- mount /dev/fd0 /mnt/floppy # Mount floppy
- cp -p /boot/chain.b /mnt/floppy # Copy chain loader
- cp -p /boot/boot* /mnt/floppy
- lilo -v -C /etc/lilo.floppy # Install lilo and the map onto floppy
- umount /mnt/floppy
Note that LILO sets the MBR to the settings as defined by the configuration file /etc/lilo.floppy.
Sample file: /etc/lilo.floppy
boot=/dev/fd0 - Floppy drive (Location of Lilo boot sector) map=/mnt/floppy/map - Locations on hard drive where the kernel can be found for boot prompt - Show prompt: LILO boot:
linear - Specific to SCSI configurations timeout=50 - Give the user time to decide (number of tenths of seconds) if there are multiple choices image=/boot/vmlinuz-2.2.17-14 - Boot this Linux kernel. This depends on your release of the operating system. label=hd_linux - Label displayed to user which identifies this kernel root=/dev/sdb6 - System instructed to boot from this drive. Unique to your system. Example: /dev/hda4 Installation dependent. initrd=/boot/initrd-2.2.17-14.img - This is specific to systems using SCSI hard drives. This line is omitted for IDE. read-only - Mount partition read-only at first to run fsck
- Actual kernel name and version will depend on your Linux release.
- Most of the information for /etc/lilo.floppy should be copied from /etc/lilo.conf
- Actual names for the files to be used may be seen in the directory /boot
- The file initrd-2.2.17-14.img is required by systems
using modular SCSI support.
It is generated using the command: mkinitrd /boot/initrd-2.2.17-14.img 2.2.17-14
and should also be copied to the floppy.
MBR restoration:Once the system has rebooted using LILO on the MBR of the floppy to point to the kernel on your hard drive, the system will boot as before.
The last step. As root execute the command: /sbin/lilo -v
This will re-install LILO on the MBR of your hard drive using the configuration file /dev/lilo.conf.
Sample file /etc/lilo.conf:
(This should already reside on your system. Generated by a Linux installation)
boot=/dev/sda - Location of Lilo boot sector. (i.e.: /dev/hda for first EIDE drive) map=/boot/map install=/boot/boot.b prompt linear default=linux timeout=50 image=/boot/vmlinuz-2.2.17-14 label=linux root=/dev/sdb6 initrd=/boot/initrd-2.2.17-14.img - This is specific to systems using SCSI hard drives. This line is omitted for IDE. read-only other=/dev/sda1 label=win98
Explanation of files:
/etc/lilo LILO configuration file /boot/boot.b Boot loader /boot/map Boot map that contains the location of the kernel /sbin/lilo Program to install lilo. Installs map.
Usage:Just boot with the floppy in it's drive. The BIOS settings may have to be changed to allow the computer to boot from the floppy drive by changing the device seek order. The floppy (A:) needs to be ahead of the hard drive (C:). To enter the BIOS configuration utility, reboot the system and press the "DEL" key while booting. (Typically. Your system may be different)
As root user (on Red Hat), use the command: /sbin/mkbootdisk 2.2.17-14
You may specify the device: /sbin/mkbootdisk --device /dev/fd0 2.2.17-14
This will of course depend on the version of the Linux kernel you are using. To obtain the kernel version see your /etc/lilo.conf file or the name of the kernel modules library directory for the information. ( ls /lib/modules/ Use the directory name of the appropriate kernel. i.e. if the directory name is /lib/modules/2.4.9-34/ then use 2.4.9-34)
- Boot computer with the floppy in it's drive.
- It will boot the kernel from the floppy but then try to use your hard drive. If successful, it will fully boot from your hard drive. It's Painless!!
- Use the command: fdisk /dev/sda (SCSI) or fdisk /dev/hda (IDE)
or whatever your drive is.
Try hda3, hda4, hda5, etc.. untill you find your partitions.
[root /root]# fdisk /dev/sdb The number of cylinders for this disk is set to 1106. There is nothing wrong with that, but this is larger than 1024, and could in certain setups cause problems with: 1) software that runs at boot time (e.g., LILO) 2) booting and partitioning software from other OSs (e.g., DOS FDISK, OS/2 FDISK) Command (m for help): p Disk /dev/sdb: 255 heads, 63 sectors, 1106 cylinders Units = cylinders of 16065 * 512 bytes Device Boot Start End Blocks Id System /dev/sdb1 * 1 3 24066 83 Linux /dev/sdb2 4 1106 8859847+ 5 Extended /dev/sdb5 4 36 265041 82 Linux swap /dev/sdb6 37 1106 8594743+ 83 Linux Command (m for help): q [root /root]#
- Mount the partition you wish to operate on:
- mkdir /mntpoint
- mount /dev/sdb6 /mntpoint
- ls /mntpoint - Shows that it works and files are accessible.
- At this point you can tar files to a tape, run lilo to repair the MBR, perform a disk check (fsck or e2fsck) or repair your system.
Copying a 3.5 inch floppy (device /dev/fd0) using Linux:
dd if=boot.img of=/dev/fd0 bs=1440k
- Insert Redhat binary install CD-ROM
- Boot from CD (You may have to change BIOS settings)
- At the boot: prompt, type linux rescue. You are then asked to chose an installation method.
- Instead of install, choose the Upgrade option but don't add any new packages. It will eventually prompt you to make a boot floppy.
- Boot from the boot floppy and mount your hard drive. i.e.: mount /dev/hda4 /hda4
You can use fdisk as shown above to investigate your drives and partitions.
This uses the GRUB files "menu.lst" and "stage2_eltorito".
- mkdir -p iso/boot/grub
- cp /lib/grub/i386-pc/stage2_eltorito iso/boot/grub
- cp /lib/grub/i386-pc/menu.1st iso/boot/grub
- Copy all files, OS files, etc to iso that you wish to put on the CD
- mkisofs -R -b boot/grub/stage2_eltorito -no-emul-boot -boot-load-size 4 -boot-info-table -o grub.iso iso
See the YoLinux tutorial on how to burn a CD or DVD.
- HOWTO: Boot Prompt
- Linux Diskcopy Script
- mkCDrec - Makes a bootable CD (El Torito) disaster recovery image (CDrec.iso) CD-ROM. Also see YoLinux CD buning tutorial.
Hard Drive repair and recovery:
- LTOOLS - command line tools to read and write Linux extended 2 filesystems from DOS
- LDE - Linux Disk Editor
- GIIS ext3/ext2FS file undelete tool.User can recover files by it's name or type or by its owner. Can't recover the files deleted before installation of giis.
- Why Recovering a Deleted Ext3 File Is Difficult
- Commercial Linux data recovery tools - list