How to fix E: Could not get lock /var/lib/apt/lists/lock - open (11: Resource temporarily unavailable) in APT

The simplest and safest solution is to wait for any running package manager to complete. Close any GUI package managers (Software Center, Update Manager) and wait a few minutes:

# Check what process is holding the lock
sudo lsof /var/lib/apt/lists/lock

If you see "unattended-upgrade" in the output, your system is installing security updates. Let this complete before running apt. You can monitor its progress:

sudo systemctl status apt-daily-upgrade.service

Wait until the service shows "inactive" status.

Use lsof to see which process holds the lock file:

sudo lsof /var/lib/apt/lists/lock

You may also check other related lock files:

sudo lsof /var/lib/dpkg/lock-frontend
sudo lsof /var/lib/dpkg/lock
sudo lsof /var/cache/apt/archives/lock

The output will show the process name and PID. Common processes include:
- unattended-upgrade: Automatic security updates
- apt-get: Another apt operation
- apt: Direct apt command
- update-manager: Software update dialog

If a process is genuinely stuck (not just slow), you can forcefully terminate it. This is safer than removing lock files:

# Find the process ID from the lsof output above
sudo kill -9 <PID>

Or use fuser to terminate all processes holding the lock:

sudo fuser -vik -TERM /var/lib/apt/lists/lock

After killing the process, repair the package database:

sudo dpkg --configure -a
sudo apt update

If no process is using the lock (lsof shows no output), the lock file may be stale. Remove it:

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

Then update your package lists:

sudo apt update

Verify that apt directories have correct ownership and permissions:

sudo chown -R root:root /var/lib/apt/
sudo chmod 755 /var/lib/apt/lists
sudo chmod 755 /var/cache/apt/archives
sudo apt update

These commands ensure the apt directories are owned by root with proper permissions.

If automated updates keep interfering with your work, you can disable them by editing the update configuration:

sudo nano /etc/apt/apt.conf.d/20auto-upgrades

Comment out (add // to the beginning) these lines:

APT::Periodic::Update-Package-Lists "1";
APT::Periodic::Download-Upgradeable-Packages "1";
APT::Periodic::AutocleanInterval "7";
APT::Periodic::Unattended-Upgrade "1";

Save with Ctrl+X, then Y, then Enter. This disables automatic background updates, allowing you to run apt manually when you choose.