RH133. 11.STEPS OF BOOT PROCESS

1. BIOS    ->Do POST ->power on self test and Check boot priority,
2. MBR     ->I stage boot loader,partition table, o/s signature
3. /etc/grub/grub.conf   ->root (hd0,0)
                           kernel /vmlinuz...... ro root=LABEL=/
                           initrd /initrd.....img
4. /etc/inittab          ->/etc/rc.d/rc.sysinit     ->Set hostname
                                                    ->Set clock
                                                    ->Enable selinux,quota
                                                    ->check filesystem
                                                    ->Enable root in rw mode
5. /etc/inittab          ->runlevel
6. /etc/rc.d/rc          ->whenever runlevel changes
7. /etc/rc.d/rc.local    ->last script executed in boot process


1. Problem  -> MBR CORRUPTED
   Corrupt  -> dd if=/dev/zero of=/dev/sda bs=446 count=1
   Error    -> Stops at boot from for long time
   Recovery -> Put first cd and reboot thn press linux rescue
                chroot  /mnt/sysimage
                grub-install  /dev/sda


2. Problem  -> grub.conf file missing  OR wrong entries in grub.conf
   Corrupt  -> mv /boot/grub/grub.conf /root
   Error    -> drops you to grub prompt
   Recovery -> root (hd0,0)
               kernel /vmlinuz...... ro root=LABEL=/
               initrd /initrd.....img

               
3. Problem  -> /vmlinuz or /initrd file missing from /boot dir.
   Corrupt  -> rm -rf /boot/vmlinuz....... rm -rf /boot/initrd.......
   Error    -> file not found
   Recovery -> Put first cd and reboot thn press linux rescue
                chroot  /mnt/sysimage
                cat /proc/sys/dev/cdrom/info  ->check cdroms identity
                mount /dev/hdb /media
                cd  /media/Server
                rpm --ivh --force kernel.................

4. Problem  -> /etc/rc.d/rc.sysinit    OR       /etc/inittab file missing
   Corrupt  -> rm -rf /etc/rc.d/rc.sysinit OR   /etc/inittab
   Error    -> cannot that execute /etc/rc.d/rc.sysinit OR No process left
   Recovery -> Put first cd and reboot thn press linux rescue
                chroot  /mnt/sysimage
                cat /proc/sys/dev/cdrom/info  ->check cdroms identity
                mount /dev/hdb /media
                cd  /media/Server
                rpm --ivh --force initscripts-8.45

5. Problem  -> Wrong entry of runlevel 0 or 6
   Corrupt  -> vim /etc/inittab and edit runlevel to 0 OR 6
   Error    -> continously reboots
   Recovery ->  Reboot machine and go to single user mode
                and edit vim /etc/initab file and change runlevel to
                3 or 5. and press init q for changes.
               


6. Problem  -> Wrong entries in the /etc/fstab
   Corrupt  -> vim /etc/fstab make some changes in the labels
   Error    -> Drops you to emergencey mode
   Recovery -> First provide roots passwd
               mount -o remount,rw /
               vim /etc/fstab ->and correct the labels  
               If you dotn know label e2label /dev/sda1
               keep checking for correct label e2label /dev/sda2
               

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