LINUX BOOTING SEQUENCE TROUBLESHOOTING

LINUX BOOTING SEQUENCE TROUBLESHOOTING

Case 1: No boot loader splash screen or prompt appears

Cause:

1) Grub.conf miss configures

2) Initrd misplaced or deleted

3) MBR cruuppet

4) /boot partition miss

Grub.conf miss configures

Remedy: try to pass boot location initrd location & kernel module location as follows

Step a) Grub > root (hd0,0)

Note: here hd0,0 means boot partition is in 1^st partition of 1^st hdd.(please use hd for SATA & SCSI hdd also )

Step b) grub > kernel /vmlinuz-$(uname -r) root=LABEL=/ rhgb quiet

Step c) grub > initrd /initrd-$(uname -r).img

Step d) grub > boot

Then after rebooting try to recreate grub.conf file

Initrd misplaced or deleted

Case a) system is up

This is the most fortunate situation for system admins who are managing the server remotely because now once the system will down it will not be up without rescue mode

Remedy:

[root@dh-localhost ~]# mkinitrd /boot/ initrd-$(uname -r).img $(uname -r)

Case b) system is down

Then boot from system via DVD & start it by rescue mode

Remedy:

Step 1) Boot: linux recue

After some process & ittrective prompt you will be on sh prompt

Step 2) chroot /mnt/sysimage

cd /boot

mkinitrd /boot/ initrd-$(uname -r).img $(uname -r)

Then reboot the system by HDD

Note: - in case of fstab is also misconfigured (ie / & other partition will not mount after boot) then chroot command will not work. So in this case your 1^st step would be to correct fstab then perform above steps as follows

Step a) boot from DVD or other bootable media

Step b) chroot /mnt/sysimage (you will find chroot error here )

Step c) mkdir /test

e2label /dev/sda1 (if it will show boot them mount it otherwise try to search by e2label /dev/sda2 ownwards)

mount /dev/sda1 /test

cd /test

cd grub

vi grub.conf (please make it correct)

mkdir /data

mount /dev/sda2 /data (mounting / partition on /data )

cd /data

cd /etc

vi fstab (please correct it )

Then reboot the system & follow previous step

Mbr corrupt

Case a) system is up

Method 1

[root@dh-localhost ~]# /sbin/grub-install /dev/sda

Method 2

[root@dh-localhost ~]# grub

grub> root (hd0,0)

grub > setup (hd0)

grub > quit

Case b) system is down

Boot system by rescue mode

Sh #Chroot /mnt/sysimage

Sh # /sbin/grub-install /dev/sda

Note : A smart system admin always take backup of MBR as follows

[root@dh-localhost ~]# dd if=/home/mbr of=/home/mbr bs=1 count 500

&

For restoration for MBR

[root@dh-localhost ~]# dd if=/home/mbr of=/home/mbr bs=1 count 500

/boot partition miss

In this case if you have backup of /boot then you can recover it otherwise you need to rebuild the server again.