Upgrading Debian 12 ("Bookworm") to Debian 13 ("Trixie")

Category: Debian
Created: 2025-11-28

Upgrading a Debian installation to the next major version number works quite smoothly. Depending on the speed of the server and the duration of the reboot, an upgrade is usually completed in under 15 minutes.

Always upgrade Debian Linux from one version to the next higher, do not skip versions!

To upgrade a server from Debian 11 to Debian 13, you must first upgrade from 11 to 12 and then from 12 to 13. Reboot the server after each upgrade!

Follow the steps below to upgrade:

update the Debian 12 packages to the latest version: apt update && apt upgrade
(otherwise, you may encounter problems when restarting OpenSSH, which could potentially lock you out.)
update /etc/apt/sources.list (replace bookworm with trixie)
if necessary, update the file /etc/apt/sources.list.d/liveconfig.list for the LiveConfig PHP repository in the same way
run apt update
run apt upgrade
run apt full-upgrade. While running, you will be asked whether some existing configuration files should be replaced - in most cases it is better to keep the existing configuration (answer with no).
run apt-get autoremove to remove all packages that are no longer required
reboot the server (that’s important to switch the kernel and all kernel modules)
then log in to LiveConfig as admin and go to Server Management → E-Mail. Save the configuration for Postfix and for Dovecot again (this will update the configuration files and adapt them for Debian Trixie).

You can also find detailed information on upgrading from Debian 12 in the official documentation.

Possible issues

If /boot is a separate partition, ensure that at least 300 MB of free space is available there.
In ProFTPD, some previously integrated modules have now been moved out, but they have not been automatically added to the (existing) modules.conf (including mod_ls.c, mod_xfer.c).
To correct this, simply save the ProFTPD configuration again in LiveConfig.
The configuration of Dovecot has changed completely in version 2.4 - to such an extent that existing configurations cannot be migrated automatically.
Therefore, save the Dovecot configuration again in LiveConfig so that it is regenerated.

Changes in Debian 13

Some things have changed with Debian Trixie (see Release Notes – in particular Things you should know about Trixie). The most important changes include:

The /tmp file system is now a tmpfs (in RAM). Files in it are therefore automatically lost when the system is restarted.
The /tmp and /var/tmp directories are regularly emptied by the systemd-tmpfiles service (can be configured via /etc/tmpfiles.d/tmp.conf).
The Postfix service has been renamed from postfix@-.service to postfix.service. If you have created manual fail2ban filters, these may need to be adjusted.