Upgrading Ubuntu 14.04 to 16.04

[sanoop]

Sounds good, keep us informed and write down the steps you took

I am not that good at English, so please excuse me.

At first i got a mail from ovh that they found some fault in my dedi box and one of there technician will intervene the system .

Dear Customer,

Our monitoring system has just detected a fault on your server ********
The fault was noticed on 2016-09-13 08:29:08



Our team of technicians on site (operational 24/7), has been informed
of the fault and will intervene on your machine.

Please be aware that other interventions may currently be in progress and
an intervention lasts on average 30 minutes per machine.

We are therefore not able to give you more details on the starting time
of the intervention.

You can see a general display of the machines currently in fault and
in intervention across our network at the following address:

 http://status.ovh.com/vms/

Your server is in rack ****

You will receive an email as soon as a technician takes charge of your
server. Meanwhile, you have can reboot it via your manager.

Logs:
----------------------
PING ********* from 213.186.33.13 : 56(84) bytes of data.
From 213.186.33.13: Destination Host Unreachable
From 213.186.33.13: Destination Host Unreachable
From 213.186.33.13: Destination Host Unreachable

--- Myserver ping statistics ---
10 packets transmitted, 0 packets received, +6 errors, 100% packet loss
---------------------

Best regards,

Kimsufi.com Customer Service
Contact: http://forum.ovh.ca

After 30 minutes i got this mail from Kimsufi

Dear Customer,

The intervention on ********** has been completed.

This operation was closed at 2016-09-13 08:04:00

Here are the details of this operation:
Diagnosis interface boot (rescue)
Date 2016-09-13 07:49:47, daniel L made Diagnosis interface boot (rescue):
Here are the details of the operation performed:
The server gets stuck during the boot phase, with the message:
(unreadahead real access)
A restart on the standard OVH kernel ('netboot') does not correct the
situation.

Actions:
Rebooting the server to "rescue" mode (Linux)

result:
Boot OK. Rescue mode accessible.

recommendations:
Configuration / error to be corrected by the customer



If you need any further information regarding this intervention, please do not hesitate to contact our technical support.

Best regards,

Kimsufi.com Customer Service
Contact: http://forum.ovh.ca

and i got the ssh username and password for the rescue ssh session . So i mounted  Linux file system partion through rescue mod using

Code:

fdisk -l

Code:

mount /dev/sda2 /mnt/

then i chrooted my hard disk using

Code:

chroot /mnt

Then i can able to start some services  apache  

Code:

service apache2 restart

, mysql

Code:

service mysql start

and ssh

Code:

service ssh start

unfortunately i was unable to start  ftp and smtp . At this point i can access all my websites including sentora panel .  Then i deleted all users which i add recently using this command to check whether  this works . Unfortunately i failed to boot it from my harddisk .  I followed all the tutorials from internet to solve "unreadahead real access" problem , But everthing failed .
And my last option is to do a release upgrade from ubuntu 14.04 to 16.04 . So i ran

Code:

sudo do-release-upgrade

I got an error  

Code:

" sudo: unable to resolve host rescue.ovh.net
Checking for a new Ubuntu release
Get:1 Upgrade tool signature [198 B]
Get:2 Upgrade tool [1,262 kB]
Fetched 1,262 kB in 0s (0 B/s)
authenticate 'xenial.tar.gz' against 'xenial.tar.gz.gpg'
extracting 'xenial.tar.gz'
Must be connected to a terminal.
"

I was unable to do the release upgrade also . So i decide to reinstall ubuntu after backingup the website files .
Conclusion : Everything i do to revamp server failed miserably.