Migration from Linux Debian 8 (Jessie) to Debian 9 (Stretch)

In order to keep your server updated, to avoid security flaws and benefit from new versions of devices currently used, you have to update your Linux Debian distribution.

Prerequisite

Before any significant operation, such as an update of base, it is essential to safeguard your datas in case of rollback.
If your server is virtualized, 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 to shift from Debian 8 Jessie to Debian 9 Stretch.
If your Debian version is lower to Jessie, please start by updating it.

Moreover, since it is a kernel update, a reboot would be unavoidable.

If possible, avoid updating via SSH, favour the terminal (it means the console on cSphere Client if you are administrator of your VMware 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 Jessie to Stretch, it is essential to make sure that Jessie 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 on Stretch then restart your server :

Check your distribution version that will show the following result :


Migration from Linux Debian 8 (Jessie) to Debian 9 (Stretch)
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