Linux Boot process :
1. POST ( power on self test ) : When we start the computer SMPS provide require supply to every device.
2. BIOS ( Basic I/O system ) : It is a small chip on motherborad , which has small program which test all the H/W device connectivity. CMOS battery provide hardware time to system.
3. MBR ( Master Boot Record ) : Once all the device test finish. It check MBR which has location of kernel.
4. GRUB ( Grand Unitfied Boot Loader ) : This is boot loader for linux ( windows boot loader is NTLDR ). The configuration file is “grub.conf” which has entries for the kernel file to use and its require parameter settings.
vzlinuz : It has parameter/settings , password to kernel.
initid.img : driver/module of kernel.
5. Kernel : As per entry in grub.conf, it load the kernel. Upto this is stage 1 of process.
6. init : this is first / parant proces which PID = 1. It check “/etc/rc.d/*” to check which services to start in process and “/etc/fstab” to look for the mount point entries.
7. Runlevel : Then it check “/etc/inittab” file and start system as per entries.
8. Login Program : If runlevel is “5” then it start with graphical interface. We enter username and password. PAM ( plugable Authentication Moduel ) check and start system desktop show.