How Does the Linux System Loads ? | Boot process of Linux | cloudpradeep

 

A Linux operating system load is similar like any other operating system. But I Linux follows mainly 6 types of processes . And that is :-

1.       BIOS

2.       MBR

3.       Grub

4.       Kernel

5.       Init

6.       Runlevel

Bios –

BIOS stands for  Basic Input and Output System. It basically perform system integrity checks. Means that BIOS searches Disk Drive, ROM, DVD drive, Usb drive to executes the bootloader programs. By pressing F12 key or F2 key you can change the boot sequence. It depends on the system.

Now BIOS gives the control to boot the operating system. Once the bootloader program is detected and loaded into the memory. In short BIOS loads and executes the MBR bootloader .

MBR –

MBR stands for Master boot records. It is located in first sector of the bootable media or disk. It ually  (  /dev/sda ). It is less then 512 bytes in size. In side the 512 bytes of disk is contents information about GRUB. In short MBR loads and executes the GRUB bootloader.

GRUB –

GRUB stands for Gran Unified Bootloader. It displays a splash screen and wait a  few second and loads the default kernel image as specified grub configuration file. GRUB has the knowledge of  configuration file system. In short GRUB  just loads the next  execute Kernel and initial RAM disk images.

Kernel –

Kernel mounts the ROOT file system as specified the GRUB configuration file . ( /boot/grub/grub.conf ) . The kernel execute the init program located in ( /sbin /int ) directory . We can verify PS commands to verify the process. Or by using this command ( ps –ef | grep init ) . In short Kernel loads the file system and load the initial programs.

INIT - 

It decides the default RUN Level.  Means It decides which initial programs will be loaded of the start-up  programs. Following the run levels

·         0 – halt

·         1 – Single user mode

·         2 – Multiuser, Without NFS

·         3 – full multiuser mode

·         4 – Unused

·         5 – X11

·         6 – reboot

Run-level –

The system now executes the Programs the current run levels.

 

 

What is log file and where it stores in Linux system?

When a computer is running, it create and store some information about PC’s health, driver details, Boot process and so on . That file is called log file. It can be helpful to troubleshoot system issues.  

Most of the log files are stores in /var/log directory.  

Log files are generated by the Linux system demon-log, syslogd.

How to find Log file in a Linux machine ?

Open the terminal and log in to Root user. Because viewing the log file we require Root permission.

Now type ( cd /var/log ) directory to access the log file.

To view the log file simple type  (  ls )

To access some special types of log file simple type this   ( sudo less [ log name ] .log .

Dmesg –

·         To view the more information about all the users who has authenticate in your machine .

·         It’s a binary file, so we can’t use ls or cat command to view the file.

·         We use last command to view the document .

Wtmp –

·         It is used to get information about all the users who has authenticated to the system.

·         It’s a binary file so we can’t use ls or cat command so we use  ( lastlog) command to view .

Journal d –

·         The main log files are stores in here journald directory.

·         It’s also a binary file so we use ( journalctl ) command to view the log file.

Journal –f  =

·         Journalctl  –f is a command to view some recent log event in the system.

·         To view or troubleshoot system error or services we use journalctl  –f command .

Logger –

·         Logger is a command to create log file manually . “logger < event name > .