# How to upgrade Debian 12 (bookworm) to Debian 13 (trixie)

> Upgrade a Debian 12 server to Debian 13 in place, the way the release notes describe, with a snapshot to fall back on and checks before and after.

Source: https://vpsnine.com/tutorials/upgrade-debian-12-to-13 · Updated: 2026-10-21

Difficulty: intermediate · Time: about 45 minutes · Tested on: Debian 12 Oldstable, Debian 13 Stable

Prerequisites:

- A server running Debian 12
- Root or a user with sudo
- A recent backup or snapshot
- About 2 GB of free disk space

To upgrade Debian 12 to Debian 13, bring bookworm fully up to date, change `bookworm` to `trixie` in your apt sources, then run `apt update`, `apt upgrade --without-new-pkgs` and `apt full-upgrade`, and reboot. Take a snapshot or backup first: there is no supported way back down.

Those are the steps from the [Debian 13 release notes](https://www.debian.org/releases/trixie/release-notes/), which are worth skimming for the packages you run. We ran the whole upgrade on a Debian 12 container with nginx, OpenSSH and cron installed, ending on Debian 13.7 with all three running. A container doesn't boot a kernel of its own, so the reboot step was not part of our test.

## Before you start

1. **Take a snapshot or backup.** If the upgrade goes wrong, restoring is far quicker than repairing.
2. **Check disk space.** `df -h /` should show at least 2 GB free. [Free some up](https://vpsnine.com/tutorials/free-up-disk-space-linux) if not.
3. **Use tmux or screen.** If your SSH connection drops mid-upgrade, the upgrade carries on and you can reattach:

   ```bash
   sudo apt install -y tmux
   tmux new -s upgrade
   ```

   If you're disconnected, log back in and run `tmux attach -t upgrade`.
4. **Note third-party repositories.** Anything in `/etc/apt/sources.list.d/` besides Debian's own (Docker, PostgreSQL, Node.js) needs its own trixie version. Check each vendor supports Debian 13 before you start.

## Bring Debian 12 fully up to date

```bash
sudo apt update
sudo apt full-upgrade
cat /etc/debian_version
```

Reboot if a new kernel was installed. Then check for problems that would get in the way:

```bash
sudo dpkg --audit
apt-mark showhold
```

Both should print nothing. `dpkg --audit` lists half-installed packages (fix them with `sudo dpkg --configure -a`); `showhold` lists packages pinned at their version, which can block the upgrade (`sudo apt-mark unhold PACKAGE`).

## Switch apt to trixie

Debian's sources live either in `/etc/apt/sources.list` (the classic one-line format) or in `/etc/apt/sources.list.d/debian.sources` (the newer format). See which you have:

```bash
grep -rn bookworm /etc/apt/sources.list /etc/apt/sources.list.d/ 2>/dev/null
```

Replace `bookworm` with `trixie` in every Debian line, including `bookworm-updates` and `bookworm-security`:

```bash
sudo sed -i 's/bookworm/trixie/g' /etc/apt/sources.list.d/debian.sources
sudo sed -i 's/bookworm/trixie/g' /etc/apt/sources.list    # if you have this file
```

Leave third-party repositories alone for now, or disable them; switch each one to its trixie version after the upgrade.

### Check it worked

```bash
grep -rn trixie /etc/apt/sources.list /etc/apt/sources.list.d/ 2>/dev/null
sudo apt update
```

The `Suites:` (or `deb`) lines now say `trixie`, `trixie-updates` and `trixie-security`, and `apt update` finishes without errors.

## Run the upgrade

The release notes do it in two stages. First a minimal upgrade, which doesn't install or remove packages:

```bash
sudo apt upgrade --without-new-pkgs
```

Then the full upgrade:

```bash
sudo apt full-upgrade
```

It downloads and installs a lot of packages; how long it takes depends on how many you have installed. Along the way, it may ask:

- **Whether to keep a configuration file you changed** (`Configuration file '/etc/ssh/sshd_config' ... What would you like to do about it?`). Answering `N` (keep your version) is the safe default. Press `D` first to see the difference. If you put your SSH settings in `/etc/ssh/sshd_config.d/`, as our [SSH guides](https://vpsnine.com/help/ssh-hardening-checklist) do, the main file is unchanged and there's no question.
- **Whether to restart services automatically.** Answer yes.

When it finishes, reboot into the new kernel:

```bash
sudo reboot
```

## Check the upgrade worked

Log back in, then:

```bash
cat /etc/debian_version
grep PRETTY_NAME /etc/os-release
uname -r
systemctl --failed
```

You should see `13.x`, `Debian GNU/Linux 13 (trixie)` and a 6.12 kernel, and `systemctl --failed` should list no units. Then check your own services one by one (`systemctl status nginx`, open the website, connect to the database).

## Clean up

Remove packages that bookworm needed and trixie doesn't:

```bash
sudo apt autoremove --purge
```

trixie's apt (version 3.0) can convert a classic `sources.list` into the newer format:

```bash
sudo apt modernize-sources
```

It keeps a `.bak` copy of the old file. Now switch your third-party repositories to their trixie versions and run `sudo apt update && sudo apt upgrade`.

## Troubleshooting

**The SSH connection dropped during the upgrade.** Log in again and `tmux attach -t upgrade`. If you didn't use tmux, run `sudo dpkg --configure -a` and then `sudo apt full-upgrade` again to finish.

**`E: The repository '... bookworm ... Release' does not have a Release file` or similar after the switch.** A third-party repository has no trixie version, or still points at bookworm. Disable that file (rename it to end in `.disabled`) and continue.

**`dpkg: error processing package ...`.** Run `sudo dpkg --configure -a`, then `sudo apt full-upgrade`. The package named in the error usually has a note in the release notes.

**Old SSH keys stop working.** OpenSSH 10 in trixie no longer supports DSA keys (`ssh-dss`). Switch to an Ed25519 key, as in [use SSH keys](https://vpsnine.com/help/ssh-keys), before you upgrade.

**The server doesn't come back after the reboot.** Use the [serial console](https://vpsnine.com/help/serial-console) to see where boot stopped, or revert to your snapshot.

## Next steps

- Running Ubuntu instead? [Upgrade Ubuntu 22.04 to 24.04](https://vpsnine.com/tutorials/upgrade-ubuntu-22-04-to-24-04).
- Read the boot's errors after the upgrade: `journalctl -p err -b`, explained in [read logs with journalctl](https://vpsnine.com/tutorials/read-logs-with-journalctl).

## Doing it on VPSNine

Take a [snapshot](https://vpsnine.com/help/snapshots) in the panel before you start; reverting to it takes a minute and undoes the whole upgrade. If you'd rather start clean, order a new server on [Debian 13](https://vpsnine.com/os/debian-13), move your data, and cancel the old one. [Debian 12](https://vpsnine.com/os/debian-12) stays available for setups that need it. See [plans](https://vpsnine.com/plans).