Crontab-scheduled task command in Linux

Firmware (CMOS/BIOS) post power-on self-check-& amp; agrave; bootstrap loader (GRUB) (load Kernel) & amp; agrave; load Kernel (driver hardware) & amp; agrave; start process init & amp; agrave; read the first stage of the execution configuration file/etc/inittab: Start of BIOS

 

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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