[The Linux Boot Process]
##BIOS
- Basic Input/Output System
- Special Firmware
- Primary purpose: find and execute the boot loader
- Performs the POST - Power On Self Test
- Contains a list of bootable devices. such as Hard disks, DBD drive, USB devices and etc
##Boot Loaders
- LILO(Linux Loader) - older
- GRUB(Grand Unified Bootloader) - Replaced LILO
##Initial RAM Disk
- initrd(initial RAM disk)
- Temporary filesystem that is loaded from disk and stored in memory
- Contains helpers and modules required to load the permanent OS file system(permanent: 영구적인)
##The /boot Directory
- Contains the files required to boot linux
- initrd
- kernel
- boot loader configuration(configuration: 구성)
ex. kernel = vmlinuz-3.13.0-46-generic, initial RAM disk example = initrd.img-3.13.0-46-generic
ls -F /boot
abi-3.13.0-46-generic initrd.img-3.13.0-46-generic
config-3.13.0.460generic System.map-3.13.0.46-generic
grub/ vmlinuz-3.13.0-46-generic
##Kenel Ring Buffer
- Contains messages from the Linux kernel
- dmesg
- /var/log/dmesg
##Runlevels/Description
- 0: Shuts down the system
- 1: Single user mode
- 2: Multi-user mode with graphical interface (Debian/Ubuntu)
- 3: Multi-user text mode (RedHat/CentOS)
- 4: Undefined
- 5: Multi-user mode with graphical interface (RedHat/CentOS)
- 6: Reboot
##Init
- Runlevels were controlled by the init program
- stored /etc/inittab:
- id:3:initdefault:
- Being phased out by systemd.
