How to fix E: Release file for URL is expired (invalid since Xd Xh Xmin Xs ago) in APT

First, check if your system's date and time are correct. This is the most common cause. The system clock is critical for validating cryptographic signatures.

# Check current date and time
date

# Check timezone
timedatectl status

# Enable automatic time synchronization (recommended)
sudo timedatectl set-ntp true

# If timedatectl doesn't work, manually sync time from NTP server
sudo ntpdate pool.ntp.org
# or
sudo systemctl restart systemd-timesyncd

Wait a few seconds after running these commands and try apt update again. If the system clock was the issue, this should resolve the error.

If updating the system time didn't work, you can temporarily bypass the validity check while investigating further. This tells APT to skip signature expiration validation for this one command.

# With apt
sudo apt -o Acquire::Check-Valid-Until=false update

# Or with apt-get
sudo apt-get -o Acquire::Check-Valid-Until=false update

# Then install packages normally
sudo apt install package-name

This allows you to proceed with package installation while you address the root cause. However, do not make this permanent without understanding why.

If you're using an end-of-life distribution or an inactive mirror, switch to an archive mirror or a more actively maintained one.

For old Debian versions (Jessie, Stretch, Wheezy), use the Debian archive instead of the regular mirror:

sudo nano /etc/apt/sources.list

Replace:
- deb http://deb.debian.org/debian buster main
- With: deb http://archive.debian.org/debian buster main

For actively supported distributions, choose a well-maintained mirror from the official list:
https://www.debian.org/mirror/list

Then test the update:

sudo apt update

If bypassing the check is necessary as a permanent solution (only after confirming it's safe), create a persistent APT configuration file:

# Create/edit the apt config
echo 'Acquire::Check-Valid-Until "false";' | sudo tee /etc/apt/apt.conf.d/99disable-check-valid-until

# Verify the file was created
cat /etc/apt/apt.conf.d/99disable-check-valid-until

Now apt commands will bypass the validity check by default. This should only be done if:
1. You've confirmed your system clock is correct
2. You understand you're accepting packages from expired repository signatures
3. You're in a controlled environment (development VM, isolated system, etc.)

Warning: Do not use this on production systems or systems exposed to untrusted networks, as it reduces security validation.

If this error occurs inside a Docker container, the issue is likely that the container image is very old. Rebuild with a fresh base image:

# Instead of this:
FROM debian:jessie

# Use a more recent version:
FROM debian:bookworm

Then rebuild your image:

docker build --no-cache -t myapp:latest .