C Y B E R I N S I G H T

Master Boot Record is the information stored in the first sector (cylinder 0, head 0) of a disk, which contains primary bootloader, which is a 512 byte image. It contains both program and a partition table. 446 bytes out of 512 bytes contains executable codes and error messages text. Next 64 bytes are partition table. Each table of 16 bytes. That is the reason why in MBR labled disks, maximum 4 partitions can be created (16 * 4 = 64 bytes). Last 2 bytes is for validation check for MBR. The job of the primary boot loader is to find stage-2 or secondary bootloader from the partition table. Then it loads boot record from the device into RAM. MBR content can be extracted by running dd command as a root user. [ dd if=/dev/sda of=/tmp/mbr bs=512 count=1 ] where /dev/sda is our HDD, /tmp/mbr is the destination file where MBR will be extracted to. As MBR is of size 512 byte,  512 block size is mentioned. As it is in binary format, to view this file in ASCII format enter [ od -xa /tmp...

Many of us are using Linux, but how many have ever wondered what exactly happens when a system is powered on, how Linux kernel is loaded, how a login screen prompts? Let's have a deep walk though Linux booting process. After reading this, one would have understanding not only on Linux booting process, but also on BIOS, UEFI firmware, MBR & GPT partitions, bootloaders like GRUB, Linux kernel etc. Let's get started . . . . In order to boot Linux, a Linux capable bootloader such as syslinux or GRUB is needed. They need to be installed in Master Boot Record (MBR) or in GUID Partition Table (GPT). Boot loader loads the kernel and initial ramdisk before actual boot process is initialized. This process is different for different firmwares such as BIOS and UEFI. When the power is on, Power On Self Test (POST) begins which ensures hardwares are ready. After it, BIOS or UEFI firmware is loaded which initializes required hardwares for booting. WHAT IS BIOS? BIOS (Basic Input ...