How to Fix The following signatures couldn’t be verified Error in Ubuntu Linux | The following signatures couldn’t be verified Error in Ubuntu Linux | Jenkins Key Download Error

GPG error: https://pkg.jenkins.io/debian-stable binary/ Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY FEF32E745F2C3D5
E: The repository 'http://pkg.jenkins.io/debian-stable binary/ Release' is not signed.

This is a very common Jenkins install issue on Ubuntu/Debian. It happens because APT no longer trusts the old Jenkins GPG key method.

Fix (Recommended Solution)

Step 1: Remove old Jenkins repo (if exists)

sudo rm -f /etc/apt/sources.list.d/jenkins.list
sudo rm -f /etc/apt/sources.list.d/jenkins*.list

Step 2: Download and install Jenkins GPG key (new method)

curl -fsSL https://pkg.jenkins.io/debian-stable/jenkins.io-2023.key \
| sudo tee /usr/share/keyrings/jenkins-keyring.asc > /dev/null

✅ This stores the key in the recommended keyrings location

Step 3: Add Jenkins repository (signed-by)

echo deb [signed-by=/usr/share/keyrings/jenkins-keyring.asc] \
https://pkg.jenkins.io/debian-stable binary/ \
| sudo tee /etc/apt/sources.list.d/jenkins.list > /dev/null 

Step 4: Update & install Jenkins

sudo apt update
sudo apt install jenkins -y 

✅ Error should now be gone