Lecture #3 Boot Loaders and Booting

Learner Outcomes

• Partition a hard disk drive to support the file system requirements for a UNIX/Linux installation
• Compare and contrast bootloaders and their accompanying configuration files
• Create and use an emergency boot disk to recover a disabled system
• Diagnose a system failing to boot and repair it

Activities

• Use fdformat and xxd to format and view a floppy disk.
• Do lab 1 - Creating a simple root file system.
• Use dd to read and write raw data, and save a copy of your MBR
• Use mkbootdisk to create an emergency boot disk, and add the ability to root to a floppy disk.

Assignment

Boot Loaders and Booting

1. The Master Boot Record
   1. Boot loader: up to 446 bytes of executable code.
   2. Partition Table: 64 bytes of information on up to 4 partitions
   3. Signature: -2 bytes: 55aa
2. Boot Loaders
   • DOS boot loader - single stage
     Simply executes the code in the first sector of the active partition.
   • SYSLinux - a dual stage bootloader
     • 512 byte stage 1 loader
     • stage 2 loader: ldlinux.sys
     • configuration file: syslinux.cfg
   • LILO boot manager
     • The lilo command builds the stage 1 boot loader
     • /boot/boot.b is the stage 2 loader
     • Configuration file: /etc/lilo.conf file
   • GRUB boot manager
     • The /boot/grub/grub.conf file
     • stage1 and stage2 boot loaders
3. The steps in Booting a Kernel:
   1. Power On Self Test (POST) - loads the BIOS
   2. BIOS loads the Master Boot Record
   3. Master Boot Loader reads its partition table to determine which partition to boot into
   4. MBL loads the boot program in the active partition
   5. Boot program presents user with a boot prompt
   6. Based upon user selection, boot program loads the desired kernel along with any supplied boot options
   7. Kernel uncompresses and loads into memory
   8. Kernel detects hardware and initializes its data
4. The dd Command
   • Can copy data within or outside of file system structures
   • Syntax: dd if=input-file of=output-file bs=blocksize count=#-of-blocks
   • Example: dd if=/dev/hda of=mbb bs=512 count=1
     Copies the master boot block to the file mbb

Relevant Commands and Files