Linux Series #5: Boot Up Process
Hello everyone. In this article, I would like to share you what I learnt — “Linux Boot Up Process”
#1
▶ The system is turned on
#2
▶ BIOS Check — System checks for all the Hardware devices. Ex. I/O Devices
#3
▶ The system looks for Boot Sector, Boot Loader ( like GRUB ) in HDD/SSD
#4
▶ Now the Linux Kernel will be loaded
#5
▶ Next, the initial RAM disk will be loaded. Basically, it contains some device drivers
#6
▶ Initialization System — File System along with all the necessary services needed by the Operating System will be loaded
#7
▶ Once all the necessary services are loaded and files system is mounted, then the initial RAM is no more needed. So it will be removed
#8
▶ Now the Initialization System continues to load the services
NOTE: All the events, processes that take place in the system will be written by the Linux Kernel into a part of RAM called “Kernel Ring Buffer”. You can also find the boot log here ( all the events that take place while the system boots up ).
Sometimes, you will come across two partition schemes — MBR and GPT
Let’s have a brief look at what are they.
MBR — Master Boot Record
▶ This is an old partition scheme which supports only 26 partitions.
▶ 3 — Primary Partitions ( Actually 4 )
▶ In case you need to have more than 3 partitions,
▶ Convert one primary partition to extended partition and have 23 more logical partitions.
▶ MBR runs only with the disks that has a maximum capacity of 2 TB only.
▶ But MBR can run in systems with Legacy Boot ( Older Systems )
GPT — GUID Partition Table
▶ You can have 128 Partitions
▶ Maximum capacity of the disk is in “Exabytes” range.
▶ Using GPT requires UEFI ( Unified Extensible Firmware Interface ) instead of traditional BIOS and a 64-bit Operating System.
Hope you got a clear idea on the boot process and partition schemes. Let me know if there is any room for improvement or change.
Originally published at http://www.justhackitnow.com.
