[SOLVED] Centos 6 - No boot after Software Upgrade - How to recover?

[LouArnold]

I have a home system in my basement. I ran Software Update and saw it go through most of the process. But I had to leave it unattended and when I came back the computer was off (not by anyone's hand). I turned the power bar to it off at that time. When I started it again, it ran through power-on, but held at a blank screen with the cursor at the top left. The power-on test shows that it detects the two hard drives and the RW-DVD drive, but its as though it can't read the boot sector on the main drive, or it can't access that drive.

All I have now is the installation DVD that I used in August to create a new V6.0 system. When I boot from it, the process quickly ends with a "boot:" prompt. If I hit enter it goes to a menu where the choices are to install a system, install drivers, rescue the system, or boot from a local drive.
Booting causes it to hang. I tried rescue, but don't know if I specifically need a rescue image. Since I don't want to re-install and configure the OS again, I'm looking for a alternative solution.

In fact, I can't tell if this is a hardware or software problem.

[Roxoff]

The rescue option is the one here you want. What normally happens is that the system will boot to a livecd-like system, search for and mount your regular system in the /mnt/sysimage directory and allow you to do whatever you need to get it working again.

If an update fails because of a power-off before it completes and the system cannot recover by itself, all you'd need to do is boot your rescue dvd, chroot to your server system (chroot /mnt/sysimage) then call yum-complete-transaction from the command line to allow it to finish the update.

In your case you cannot do this - for some reason you have your system failing before the boot-up is complete. This suggests you have a hardware failure, and instant shut-offs are usually caused by heat build up or power supply failure (or, potentially both - one can cause the other). If it were my system, I'd do the following (while observing all anti-static precautions), and testing after each stage:

* Check for clogged fans and ensure they all turn when the power is applied, cleaning them with a soft brush and a clean-air aerosol can would help.
* Clean any build-up of crud off the mainboard, paying particular attention to areas around fan outlets which can become clogged the easiest (i.e. near the video card fan or close to case fans and where the cpu fan output is).
* Check components - ensure all your PCI devices are seated correctly in the mother board, and that there is nothing that's fallen across them or is littering them. Clean any mess off them like you did the main board.
* Try running it with the case open for a while - if it's heat then this can often help - but be careful to ensure nothing can fall inside while it's switched on (this is only a test, remember).
* Check the power supply is working safely, check for any burning smell coming from it - it's not normally recommended that you open the psu, if it's all clogged up inside it'll hinder its performance. If you suspect it's the psu, though, you should really replace it. You could buy a cheap one to test that things are working ok (or, if you have one laying about, or in another computer, you could replace it temporarily to see if things work smoothly from then on)
* Run memtest86 to see if the RAM has developed any faults.
* There are hard disk testing tools available from several of the manufacturers - you may want to try and get hold of them if you can to test any drives you have.

[LouArnold]

To Roxoff:
Recovery was accomplished with the Installation CD - the rescue software worked better than I expected although I got lost in it a few times. Re-installing grub solved the matter.

After recovery, I started software update again and 215 changes were listed. I began the process and watched for awhile, but left it unattended. When I got back the screen was off and the computer was quiet - but not off. Touching the mouse brought it back on and I saw the update had completed. My guess is that, in the previous attempt, I shut the computer off while it was still running, and so the bootstrap somehow got destroyed (I'm guessing.) But thanks for your help.

[arvin1844]

try to enter in single user mode.for that when reboot your system and press Esc.Then press 'e' by selecting your os if you have 2 or more os.Select kernel and press 'e' again and give a space and type 's' at the end of the line.Then press enter and press 'b' .
your system will rebooted into single user mode.In the console give "#mount -o remount rw /".It will remount your file system to get read write permission.
then look in /etc/fstab and check whether there is any invalid entry..if then remove it and reboot

[LouArnold]

try to enter in single user mode.for that when reboot your system and press Esc.Then press 'e' by selecting your os if you have 2 or more os.Select kernel and press 'e' again and give a space and type 's' at the end of the line.Then press enter and press 'b' .
your system will rebooted into single user mode.In the console give "#mount -o remount rw /".It will remount your file system to get read write permission.
then look in /etc/fstab and check whether there is any invalid entry..if then remove it and reboot

Thank you. But I already solved the problem.

This tread has ended as far as I'm concerned.