# SOLVE: Waiting for cache lock: Could not get lock: /var/lib/dpkg/lock-frontend. (Ubuntu Focal, Rasberry Pi 3 Model B+) > Author: Junner > Date: 5/8/2025 After using `sudo apt upgrade`, terminal showed: > Waiting for cache lock: Could not get lock: /var/lib/dpkg/lock-frontend. It is held by process 3399. I checked the process name by ``` ps -A | grep 3399 ``` The process is `unattended-upgr`. I knew it's a system service for upgrading packages regularly. I can't turn it off with ``` sudo systemctl stop unattended-upgrades.service ``` By doing this, it'll hold there, no terminated. But we can terminate it by `kill`. Before doing this, let's carefully looking at who's locking. ``` sudo lsof /var/lib/dpkg/lock-frontend ``` Someone told me that several processes might there. But for me there was only 3399. And `kill` them all: ``` sudo kill -9 3399 ``` The service will restart immediately. So now we should turn the service off. ``` sudo systemctl stop unattended-upgrades.service ``` After rebooting the machine, `unattended-upgrades.service` will restart. So no worries. Now we can `sudo apt upgrade`.