How to apt-delete-repository?

I would like to run the reverse of this command to remove the non-compatible repository in Debian 8.1

sudo add-apt-repository -y ppa:nemh/systemback

where the command add-apt-repository is in the package software-properties-common.
I could not find the systemback entry in /etc/apt/sources.list.

How can you run the reverse of the command?

Answers:

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Method 1

To remove a repository, you have to do 2 things:

• Remove it from sources.list.

  If it was added by add-apt-repository then you will find it in its own file in /etc/apt/sources.list.d, not in the main sources.list.

  sudo rm /etc/apt/sources.list.d/nemh-systemback-precise.list

• Optional: Stop trusting the key

  Use apt-key list to list trusted keys. Look for an entry like “Launchpad PPA for Kendek” in this case. Then use apt-key del to delete it:

  sudo apt-key del 73C62A1B

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0