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unattended-upgrades can install eligible Debian security updates automatically, but its presence and active configuration vary by machine. Check the package, APT settings, repository-origin rules, and schedule on the system you want to protect; do not assume automatic updates are enabled just because it runs Debian.
What unattended-upgrades does
unattended-upgrades is an APT package that installs eligible upgrades from the package sources configured on the system. It does not bypass APT: periodic settings determine when it runs, while origin and suite rules determine which packages qualify. Debian describes it as intended primarily for security upgrades on stable systems. Debian Reference
The program guards against package configuration-file prompts that would otherwise require an interactive response. It is commonly invoked by apt-daily-upgrade.service or cron. The Debian Bookworm manual documents /etc/apt/apt.conf.d/50unattended-upgrades as its default configuration file. Debian Bookworm unattended-upgrade manual
Is unattended-upgrades enabled by default?
Not reliably enough to assume it is active on your machine. Debian’s PeriodicUpdates wiki says many installations use conservative settings, but the package may be missing or disabled. Package presence alone also does not prove that APT is configured to run upgrades or that the relevant timers are active. Verify each part on the target system. Debian PeriodicUpdates wiki
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How do I enable automatic security updates on Debian?
1. Check or install the package
Check whether the package is installed:
dpkg-query -W -f='${Status}n' unattended-upgradesIf it is not installed, install it with APT:
sudo apt update
sudo apt install unattended-upgradesPackage status confirms installation only; continue to check enablement and scheduling.
2. Enable unattended upgrades
Run Debian’s configuration dialog:
sudo dpkg-reconfigure unattended-upgradesChoose the option to enable automatic stable updates when prompted. The exact dialog and resulting configuration can depend on the installed release and package version, so inspect the files afterward rather than treating the prompt as proof that all desired settings are active. Debian documents this command as an enablement route. Debian PeriodicUpdates wiki
3. Inspect APT’s periodic settings
Review the APT configuration fragments under /etc/apt/apt.conf.d/, including any local overrides. Debian Reference gives these example settings for refreshing package lists and invoking unattended upgrades:
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APT::Periodic::Unattended-Upgrade "1";These values are configuration examples, not a guarantee of a particular interval on every host. Check the release-specific configuration and how its APT timers or cron jobs are set up. Debian Reference
4. Check the schedule
On systems using systemd, inspect the APT timers and their next and last activation times:
systemctl list-timers 'apt-daily*'
systemctl status apt-daily.timer apt-daily-upgrade.timerDebian’s wiki identifies apt-daily.timer as the common path for package-list downloads and apt-daily-upgrade.timer for upgrades. A timer’s existence does not establish that the upgrade settings or eligible origins are correct; review those separately. Hosts may use a different execution path, including cron. Debian PeriodicUpdates wiki
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Which packages will be installed automatically?
The configured repository metadata and allowed-origin rules determine eligibility. Inspect /etc/apt/apt.conf.d/50unattended-upgrades and any later-sorting configuration fragments for Unattended-Upgrade::Allowed-Origins or Unattended-Upgrade::Origins-Pattern. Debian’s package README explains that origin and suite or archive information comes from repository Release files and can be examined with apt-cache policy. unattended-upgrades 2.12 README
Debian’s wiki describes the default aim as automatically installing security updates, rather than new features, but the exact package set depends on the installed release’s shipped configuration and local overrides. Do not broaden allowed origins without checking what those repositories contain. Put local changes in a later-sorting APT configuration fragment instead of editing package-shipped defaults in place; this helps keep local policy separate from package updates. unattended-upgrades 2.12 README
Choose the right level of automation
| Choice | What it means | Trade-off |
|---|---|---|
| Stable release, security-focused origins | Automatic installation is limited by the stable release’s configured eligible origins. | Reduces the delay before security fixes are applied while keeping scope narrower than a broad upgrade policy. Debian says unattended upgrades are mainly intended for security upgrades on stable. |
| Testing or unstable release | Packages change more broadly as those distributions evolve. | Debian Reference cautions against unattended upgrades on testing or unstable because the system can eventually break; manual supervision gives more opportunity to assess changes. |
| Download or list updates for later review | Use APT periodic behavior to refresh package lists or download upgradeable packages without automatically installing all eligible updates. | Preserves an approval step, but fixes may remain unapplied until someone reviews and installs them. Available behavior depends on periodic settings. |
| Automatic installation with monitoring | Allow eligible updates to install and regularly inspect logs and package outcomes. | Reduces routine delay and manual work, but requires operational monitoring and a recovery plan for problems. |
These are operational choices, not quantified risk rankings: Debian’s documentation does not provide a universal schedule or measured failure rates. The guidance on stable versus testing and unstable is in the Debian Reference.
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Review logs
The Debian Bookworm manual lists the main unattended-upgrades log and the separate dpkg log:
/var/log/unattended-upgrades/unattended-upgrades.log/var/log/unattended-upgrades/unattended-upgrades-dpkg.log
Also review /var/log/dpkg.log for package-manager activity. A lack of recent entries may mean the schedule has not run, no packages qualified, or another configuration issue is involved; use the timer status and APT settings to narrow down the cause. Debian Bookworm unattended-upgrade manual Debian PeriodicUpdates wiki
Simulate or enable debug output
To simulate an update without installing it, run:
sudo unattended-upgrade --dry-runFor diagnostic output, run:
sudo unattended-upgrade -dThe dry run is useful for seeing what the current configuration would select; it does not prove a future scheduled run will succeed. The -d option enables debug output in the Bookworm manual. Debian Bookworm unattended-upgrade manual
Consider package-change and bug notifications
Debian’s wiki suggests apt-listchanges for notifications about package changes. Email delivery may require a configured local mail transfer agent; installing a notification package alone does not ensure mail reaches an administrator. Debian PeriodicUpdates wiki
The Debian Handbook notes that apt-listbugs, when installed, can prevent automatic installation of packages associated with reported serious or grave bugs. This safeguard depends on that package being installed and configured. Debian Handbook: Automatic Upgrades
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