1. Back up your current sources list.

sudo mv /etc/apt/sources.list /etc/apt/sources.list_bak

2. Create a new sources list.

sudo nano /etc/apt/sources.list

3. Paste the following contents and save.

deb http://us.archive.ubuntu.com/ubuntu/ artful main restricted
deb http://us.archive.ubuntu.com/ubuntu/ artful-updates main restricted
deb http://us.archive.ubuntu.com/ubuntu/ artful universe
deb http://us.archive.ubuntu.com/ubuntu/ artful-updates universe
deb http://us.archive.ubuntu.com/ubuntu/ artful-backports main restricted universe multiverse
deb http://archive.canonical.com/ubuntu artful partner
deb http://security.ubuntu.com/ubuntu artful-security main restricted
deb http://security.ubuntu.com/ubuntu artful-security universe

4. Update your packages list to enable the new sources list.

apt update

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