How to fix E: Could not open lock file /var/lib/dpkg/lock-frontend - open (13: Permission denied) in APT

The simplest and most common fix is to prefix your apt commands with sudo to run them with administrative privileges:

sudo apt update
sudo apt install package-name
sudo apt upgrade

This grants the apt command the necessary permissions to access the dpkg lock files. Always use sudo when running any apt or dpkg commands that modify the system.

Ubuntu and Debian systems often run automatic background updates that lock the package manager. Wait 10-15 minutes for these processes to complete naturally before trying again.

You can check if apt is currently running:

ps aux | grep -i apt

If you see unattended-upgrade or apt processes, let them finish. This is the safest approach.

If background updates don't seem to be the issue, check what process is holding the lock file:

sudo lsof /var/lib/dpkg/lock-frontend

This command shows which process (if any) has the lock file open. If no output appears, the lock file exists but isn't being used by any running process—likely a leftover from a previous operation.

You can also check for any stuck apt processes:

ps aux | grep apt

If a process is hanging and preventing package operations, you can terminate it. First, identify the PID from the previous step, then:

# For graceful termination
sudo kill PID

# For forced termination (if the process won't stop)
sudo kill -9 PID

Replace PID with the actual process ID. After killing the process, run:

sudo dpkg --configure -a

This command completes any interrupted package installations and cleans up the system state.

Only do this if you're certain no package manager is running. Removing lock files while apt is active can corrupt your package database.

First, verify no apt processes are running:

sudo lsof /var/lib/dpkg/lock-frontend

If no output appears, you can safely remove the stale lock files:

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

Then reconfigure dpkg:

sudo dpkg --configure -a
sudo apt update

If the lock persists despite trying the above steps, rebooting the system will clear any stuck processes and lock files:

sudo reboot

After rebooting, the lock file issue should be resolved and you can run apt commands normally with sudo.