Upgrading from GNU Linux Debian 7 (Wheezy) to GNU Linux Debian 8 (Jessie)

In order to keep your server updated, to avoid security flaws and benefit from new versions of services currently used, you should keep your Linux Debian distribution up-to-date.

Prerequisite

Before any significant operation, such as a database update, it is essential to safeguard your data: a rule of thumb is that any system may encouter a critical failure (think : how may i be impacted in case of data loss).
If your server is a virtual machine, you can ask for an instantaneously saving of your VM (snapshot) that you can complete with a manual saving, either through integrated tools of applications software that you administrate (i.e Backup of Plesk function) or manually.

Here is the way to manually safeguard some important folders:

Be careful, it is only possible (read : recommanded) to shift your debian from previous-version to current-version (ex : from Debian 7 Wheezy to Debian 8 Jessie).
In our case, if your Debian version is lower than Wheezy, please start by updating it.

Moreover, since it is a kernel update, a reboot would be unavoidable (you may use kexec to minimize your downtime).

If possible, avoid updating via SSH, favour local terminal (read : the console of you VM if you are a VM administrator or via a remote/virtualized KVM) to avoid the cutoff right in the middle.
Put a stop to all critical services such as Apache, MySQL, etc, to avoid any issue while updating.


Update

Before upgrading your server from Wheezy to Jessie, it is essential to make sure that Wheezy is updated :

Edit your file /etc/apt/sources.list to replace the words wheezy by Jessie or use the command sed to do the modification :

Perform again step 1 to upgrade to Jessie then restart your server :

Check your distribution version that will show the following result :


Upgrading from GNU Linux Debian 7 (Wheezy) to GNU Linux Debian 8 (Jessie)
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