Firmware (CMOS/BIOS) post power-on self-check-à bootstrap loader (GRUB) (Load Kernel) à load Kernel (driver hardware) à START process init à read execution configuration file/etc/inittab
Stage 1: BIOS startup
1. After pressing the power supply, execute-power-on self-check.
Firmware-programs between software and hardware
Detect cpu, memory, video card, keyboard, etc.
Phase 2: GRUB boot guide phase
2. After self-check is passed, execute the self-lifting program
GRUB load the kernel self-starting Program
Read the/boot/grub. conf file and display the Startup menu.
Stage 3: Kernel stage
3. Kernel
Run kernel startup parameters
Driver hardware
Running level (7 types)
Ü Halt Shutdown
Ü Single user mode (no graphical interface, only root users can log on)
Ü Multiuser does not share nfs files.
Ü Full character interface multi-user interface
Ü Unsed custom
Ü Xll graphical multi-user mode
Ü Reboot restart
Id: 5: initdefault
# Runlevel view running level
# Init [0123456Ss] Run-level switch
Stage 4: Initialize sys V init
Start Process init ----- read configuration file
Grep command
Grep-v '^ #'/etc/inittab | more
Extract valid rows
Inittab File Analysis
Id: run-levels: action "process
Id: identifier, generally two digits or letters
Run-level: Specifies the running level. You can specify multiple
Action: Specifies the running status
Process: Specifies the script/command to run.
Firmware ------ bootloader --- kernel --- init ---/etc/inittab --- initdefault ----/etc/rc. d/rc. sysinit ---/etc/rc. d/rc ----/etc/rc. d/rcN. d N = 0-6 ----- username password
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