Upgrade Ubuntu 14.04 LTS to Ubuntu 16.04 LTS

If you are still running Ubuntu 12.04 on your server, you must first upgrade to Ubuntu 14.04. Instructions can be found here.
Please note that the support period for Ubuntu 12.04 LTS will expire in 2017. After expiration, no updates for Ubuntu 12.04 are provided by the operating system manufacturer.

Upgrade procedure

Preparation

Download the script with this command:

wget --no-check-certificate https://install.keyhelp.de/scripts/keyhelp_ubuntu_upgrade_14_to_16_php5 -O keyhelp_ubuntu_upgrade_14_to_16.php

Afterwards start script with:

php keyhelp_ubuntu_upgrade_14_to_16.php

1.)
Follow the instructions of the script. It will automatically run necessary tasks in preparation for the upgrade. Your current operating system will be updated.

2.)
During the course of the script the control of the program flow is hand over to "do-release-upgrade". Please follow the instructions of the program and answer the questions (see below). Note, that depending on the services installed on your server, perhaps more questions arise.

• Continue running under SSH? ⇒ Yes
  
• Note SSH ⇒ [ENTER]
• Third party sources disabled ⇒ [ENTER]
• Do you want to start the upgrade? ⇒ >Yes
  
• Restart services during package upgrades without asking? ⇒ <YES> / <NO> ( Decision is up to the user )
• Configuration file »/etc/default/spamassassin« ⇒ Keep your currently-installed version
• Configuration file »/etc/spamassassin/local.cf« ⇒ Keep your currently-installed version
• Configuration file »/etc/apache2/conf-available/security.conf« ⇒ Keep your currently-installed version
• Configuration file »/etc/apache2/mods-available/ssl.conf« ⇒ Keep your currently-installed version
• Configuration file »/etc/awstats/awstats.conf« ⇒Keep your currently-installed version
• Configuration file »/etc/init.d/proftpd« ⇒Keep your currently-installed version
• Configuration file »/etc/apache2/suexec/www-data« ⇒ Keep your currently-installed version
• Configuration file »/etc/opendkim.conf« ⇒ Keep your currently-installed version
• Configuration file »/etc/apt/apt.conf.d/50unattended-upgrades.ucftmp« ⇒ Keep your currently-installed version
• Remove obsolete packages? ⇒ Yes
  
• Restart required ⇒ Yes
  

3.)
Please execute the following command after the restart:

phpenmod ioncube

Afterwards restart the script again with:

php keyhelp_ubuntu_upgrade_14_to_16.php

4.)
Follow the instructions of the script. The last step completes the upgrade. Your system will then be restarted.
Congratulations, you now use KeyHelp with Ubuntu LTS 16.04!