How to fix unattended-upgrades: dpkg was interrupted, you must manually run 'dpkg --configure -a' in APT

First, verify that dpkg is indeed in an interrupted state by running:

sudo dpkg --configure -a --dry-run

The --dry-run flag shows what would be configured without actually making changes. This lets you see which packages are waiting to be configured without taking action yet.

Once you've confirmed the pending configurations, run the command to actually complete them:

sudo dpkg --configure -a

This command goes through all packages that have been unpacked but not yet fully configured and completes their installation. This typically takes a few minutes depending on how many packages are waiting.

After dpkg completes, update your package lists and check for any remaining issues:

sudo apt update
sudo apt --fix-broken install

The --fix-broken install command will install any missing dependencies or fix any remaining broken package states. This ensures your system is fully consistent before resuming automatic updates.

In rare cases where dpkg lock files are stuck, you may need to remove them. Only do this if dpkg is completely hung and unresponsive:

sudo rm -f /var/lib/dpkg/lock
sudo rm -f /var/lib/dpkg/lock-frontend
sudo rm -f /var/cache/apt/archives/lock

After removing lock files, run dpkg again:

sudo dpkg --configure -a

Lock file removal should only be a last resort when the system is truly deadlocked.

After resolving the dpkg state, verify that your package system is consistent:

sudo apt-get check

This command checks for broken package dependencies without making any changes. If it completes without errors, your system is ready for normal operations.

To prevent this error from appearing in the future, configure unattended-upgrades to automatically repair interrupted dpkg state. Edit the configuration file:

sudo nano /etc/apt/apt.conf.d/50unattended-upgrades

Find or add the following line (it may already be there):

Unattended-Upgrade::AutoFixInterruptedDpkg "true";

If it's set to false or missing, change it to true. This setting makes unattended-upgrades automatically run dpkg --configure -a if it detects an interrupted state, preventing manual intervention from being required:

sudo systemctl restart unattended-upgrades

Restart the service to apply the configuration change.

Review system logs to understand what caused the dpkg interruption originally:

sudo journalctl -xe | tail -50
sudo tail -100 /var/log/unattended-upgrades/unattended-upgrades.log

Look for:
- Unexpected reboot messages
- Power failure indicators
- Disk space warnings (No space left on device)
- Kernel panic messages

Understanding the root cause helps prevent future interruptions. For example, if disk space was the issue, you may need to clean up or expand your filesystem.