Issues related to Ubuntu OS or related distributions
If you want to delete an wrong or non-working repository you can listed and delete by going to:
$ cd /etc/apt/sources.list.d
$ ls
docker.list elementary.list owncloud.list patches.list
so first we need to list the repositories to determine which will be removed:
$ sudo apt-key list
/etc/apt/trusted.gpg
--------------------
pub rsa2048 2015-09-28 [SC] [expires: 2022-05-28]
06D7 EADE 708A 40FA 136E B454 0700 205D FD41 A71A
uid [ unknown] devel OBS Project <devel@s2.owncloud.com>
/etc/apt/trusted.gpg.d/elementary.key.asc
-----------------------------------------
pub rsa1024 2011-10-01 [SC]
6C87 69CE DC20 F5E6 6C3B 7D37 BF36 996C 4E1F 8A59
uid [ unknown] Launchpad PPA for elementary OS team
in this case we will delete the owncloud repository 06D7 EADE 708A 40FA 136E B454 0700 205D FD41 A71A
by using:
$ sudo apt-key del "06D7 EADE 708A 40FA 136E B454 0700 205D FD41 A71A"
OK
$ sudo apt-get update