How to Upgrade Debian 8 (Jessie) to 9 (Stretch) safely
This tutorial explains the procedure to upgrade Debian 8 to 9 in a few simple steps.
Before you start with the upgrade, backup all critical data. That’s especially the config data in the /etc directory and the user data in /home. When you run a server then you should include the databases (MySQL, Postgresql, etc), web and email data in the backup as well. The backup should be stored on an external hard disk, on an external server e.g. by FTP or on a cloud drive. Here are a few examples of how to create backups with tar.
Backup the configuration and data
Configuration files in the /etc directory.
tar -pczf etc.tar.gz /etc
Backup of the /var/www website directory.
tar -pczf www.tar.gz /var/www
Backup of the /home directories.
tar -pczf home.tar.gz /home
For ISPConfig 3 users: Backup of your email server files.
tar -pczf vmail.tar.gz /var/vmail
Backup MySQL databases.
mysqldump --defaults-file=/etc/mysql/debian.cnf -cCeQ --hex-blob --quote-names --routines --events --triggers --all-databases -r all_databases.sql
Then move the tar.gz and .sql files for safe storage on a backup drive.
Check the apt sources.list file
We will install all available Jessie updates first before we upgrade to Jessie. On some systems, the package source is defined as “stable” in the sources.list file instead of “jessie” or “stretch”. To avoid an accidental early upgrade to Stretch, please check the sources.list now and ensure that it contains “jessie” and not “stable” as source:
Use a command line editor like nano or vi to open /etc/apt/sources.list, the lines should be similar to the ones below:
deb http://httpredir.debian.org/debian jessie main contrib non-free
deb http://httpredir.debian.org/debian jessie-updates main contrib non-free
deb http://security.debian.org jessie/updates main contrib non-free
Update the packages for Debian 8
The following commands will install all pending Jessie updates. This ensures that your system is in a good shape for the update to Stretch.
Ready for the first upgrade:
Follow this with:
Check the package state to ensure that no packages are on hold or in half installed state
This test is important, we will check the package state to ensure that no packages are on hold or in half installed state. Your system and apt database must be in a good shape before we proceed with the dist upgrade. If there are any broken or “on hold” packages, then fix these issues before the upgrade.
Check that no packages are on hold by querying the package database with the dpkg command:
dpkg --get-selections | grep hold
When both commands did not return any packages, then proceed with the upgrade.
Update the sources.list for Debian 9
Edit the /etc/apt/sources.list file again:
and replace its content with the following lines:
deb http://httpredir.debian.org/debian stretch main contrib non-free
deb http://httpredir.debian.org/debian stretch-updates main contrib non-free
deb http://security.debian.org stretch/updates main contrib non-free
Save the file and run the following command to update the sources database:
Check if packages are upgradable
We can test with apt command if the installed packages are upgradable. Run this command to perform the test:
apt list --upgradable
Debian 8 to 9 Update in two steps
It is recommended to do the upgrade in two steps, first run “apt-get upgrade” to install the base packages and then run “apt-get dist-upgrade” to do the actual distribution upgrade,
Start with the update by running this command:
Next, we will do the distribution upgrade by running:
A reboot is required to finish the upgrade and load the new kernel:
Check the update
To check which Debian version is currently installed on the system, take a look at the file /etc/os-release.
The result on a Debian Stretch system is:
- Debian: http://www.debian.org/