Upgrading Debian 8 ‘Jessie’ to Debian 9 ‘Stretch’

Intro

Debian 9 Stretch was released as the latest stable version of the Linux Distribution: Debian. While it’s always possible to install Debian 9 fresh from scratch, it’s also possible to perform an in-place upgrade from Debian 8. The following post describes the necessary steps to do so.

For a incredibly thorough documentation of the process, I suggest you also read through the official release notes.

Notes:

  • Upgrading to Debian 9 Stretch is only supported from Debian 8 Jessie. If you are running a version older than 8, you must first upgrade to 8 before working through this process.
  • The upgrade involves a kernel update, so a reboot will be required toward the end of the process.
  • It is strongly recommended that you have a full system backup or backup of any important data before proceeding with the upgrade, ensure that you have a plan to roll back. In the case of a virtual machine, take a snapshot before starting.

Performing the upgrade to Debian 9 Stretch

Before proceeding with the upgrade, please read through the list of issues to be aware of when upgrading to Stretch.

  1. It is recommended that you have your Debian 8 Jessie installation completely up to date before starting, to do this run “apt-get update” followed by “apt-get upgrade” and install available updates.
root@debian8:~# apt-get update
root@debian8:~# apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

In this case all updates have been applied already, so it’s fine to proceed.

Edit the /etc/apt/sources.list file, my file is shown below. As you can see all of the lines are currently specifying “jessie”. Note that your mirror sources will likely be different which is fine.

deb http://ftp.ch.debian.org/debian/ jessie main
deb-src http://ftp.ch.debian.org/debian/ jessie main

deb http://security.debian.org/ jessie/updates main contrib
deb-src http://security.debian.org/ jessie/updates main contrib

# jessie-updates, previously known as 'volatile'
deb http://ftp.ch.debian.org/debian/ jessie-updates main contrib
deb-src http://ftp.ch.debian.org/debian/ jessie-updates main contrib

Change the instances of “jessie” to “stretch”, you can either do this manually, or automatically with the below sed command.

sed -i 's/jessie/stretch/g' /etc/apt/sources.list

You can either use “stretch” or “stable”, as Debian 9 Stretch is now the current stable version as of writing. However note that if you use stable instead of the specific release name, in future when Debian 10 is released that will be the stable version so you may upgrade to that unintentionally.

The recommended way to upgrade Debian is with the ‘apt-get’ command. First update the list of available packages with the below command, as we’ve just updated the sources.list file.

apt-get update

Use “apt list –upgradable” command to quickly see what will be installed, updated, and removed during the upgrade process without affecting the system.

apt list --upgradable

Sample Output:

unattended-upgrades/stable 0.93.1+nmu1 all [upgradable from:0.83.3.2+deb8u1]
util-linux/stable 2.29.2-1 amd64 [upgradable from: 2.25.2-6]
uuid-runtime/stable 2.29.2-1 amd64 [upgradable from: 2.25.2-6]
vim/stable 2:8.0.0197-4 amd64 [upgradable from: 2:7.4.488-7+deb8u3]
vim-common/stable 2:8.0.0197-4 amd64 [upgradable from: 2:7.4.488-7+deb8u3]
vim-runtime/stable 2:8.0.0197-4 all [upgradable from: 2:7.4.488-7+deb8u3]
vim-tiny/stable 2:8.0.0197-4 amd64 [upgradable from: 2:7.4.488-7+deb8u3]

Now that the list of available packages has been updated from the mirror, run the below command to perform a minimal upgrade.

apt-get upgrade

This is known as a minimal system upgrade as it only upgrades packages that can be upgraded without needing any other packages to be removed or installed, so it’s a safe place to start. This upgraded 932 packages requiring 412MB on my system.

Now you’re ready to do the complete system upgrade, this will upgrade to the latest available version for all packages installed.

apt-get dist-upgrade

Ensure that you have enough free disk space to complete the operation, in my case it notes that afterwards 1,048MB of additional disk space will be used with 639 package upgrades and 479 newly installed packages.

During the distribution upgrade, services installed on your system needs to be restarted after up gradation of each service packages (ex. Apache, NTP) which may cause you the service interruptions. You can choose to restart automatically during upgrade or manually after the upgrade. Here, I opted to do “an automatic restart of services during the OS upgrade“.

Verify upgrade:

Reboot your machine after the distribution upgrade.

reboot

Verify the current version of Debian operating system.

lsb_release -a

Distributor ID: Debian
Description: Debian GNU/Linux 9.0 (stretch)
Release: 9.0
Codename: stretch

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