Lost SSH session during upgrade

I was in the middle of an upgrade when someone accidentally closed my terminal. When I tried to restart the apt upgrade process, I encountered an error message about a lock file being held.

This was on a machine running production applications, so I needed to resolve the issue quickly and minimize the risk of causing any downtime or further issues. After some research, I found a straightforward and effective solution.

The Problem: Locked apt Process

When apt is running, it creates a lock file to prevent other package management processes from interfering. If the process is interrupted unexpectedly — like when my terminal was abruptly closed — this lock file might not be removed properly. As a result, any subsequent attempts to run apt will fail with a message like:

E: Could not get lock /var/lib/dpkg/lock-frontend.

The Solution: Safely Removing the Lock

To resolve this issue, I could follow these steps and successfully complete the upgrade:

sudo killall apt # to release the lock
sudo dpkg --configure -a # to fix the interrupted upgrade
sudo apt upgrade # to make sure no packages are left not upgraded

As you can imagine, this was nerve-wracking, but having a solid plan in place made all the difference. Additionally, knowing we had backups gave us peace of mind — if the problem persisted, we could at least roll back to a recent backup.