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Bootstrapping
● Loads basic software into memory of computer
● Executes JUMP command● Tells the location of BIOS program in ROM
Step 2: MBR
● Found in /dev/sda or /dev/hda● Size: < 512 bytes● Contains info about GRUB● Executes GRUB bootloader
Step 3: GRUB
● GRand Unified Bootloader● Can choose which kernel to be executed● Displays a screen for a few seconds● Default kernel image: /boot/grub/grub.
cfg
Step 5: init
● init daemon starts processes from /etc/inittab
● init identifies default init level and uses to load appropriate program
/etc/inittab
● id:rstate:action:process● id - identifier of the entry● rstate - lists the runlevels● action - which action to be taken● process - process to start, monitor or
restart if terminated
Run levels
6 run levels:● 0 - halt● 1 - Single user mode● 2 - Multiuser without NFS● 3 - Full Multiuser mode● 4 - unused● 5 - X11● 6 - Reboot
Runlevel programs
● Run level 0 – /etc/rc.d/rc0.d/● Run level 1 – /etc/rc.d/rc1.d/● Run level 2 – /etc/rc.d/rc2.d/● Run level 3 – /etc/rc.d/rc3.d/● Run level 4 – /etc/rc.d/rc4.d/● Run level 5 – /etc/rc.d/rc5.d/
/etc/rc.d/rc*.d
● rc scripts are run control scripts● Programs which starts with S are used for
Startup● Programs which starts with K are used for
Shutdown
References:
● http://mastro77.blogspot.in/2014/09/have-you-ever-wondered-what-happens.html
● http://mastro77.blogspot.in/2014/09/initrd.html