How to fix apt-get source You must put some 'source' URIs in your sources.list

Problem:

You want to download an apt source package using

apt-get source <package name>

but instead you see this error message:

E: You must put some 'source' URIs in your sources.list

Solution

In most cases, you can fix this easily using

sudo apt-get update

If this does not fix the issue, edit /etc/apt/sources.list, e.g. using

sudo nano /etc/apt/sources.list

and ensure that the deb-src lines are not commented out.

Example: You need to change

deb http://archive.ubuntu.com/ubuntu artful main restricted
# deb-src http://archive.ubuntu.com/ubuntu artful main restricted

to

deb http://archive.ubuntu.com/ubuntu artful main restricted
deb-src http://archive.ubuntu.com/ubuntu artful main restricted

and run sudo apt update after changing the file.

If there are repositories without a deb-src line, you can often try to copy the deb line - for example, from

deb http://myserver.com/deb focal main

you can create an additional line

deb-src http://myserver.com/deb focal main

by changing deb to deb-src and running sudo apt update afterwards. This often works, but it depends on the repository.