apt-get update produces the error

[Colin Watson]

On Tue, Dec 13, 2016 at 08:26:35AM -0000, Grizzly wrote:
> When I run "apt-get update" it sems to work but ends with
> 
> W: The repository 'http://extras.ubuntu.com/ubuntu xenial Release' does not have a Release file.
> N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
> N: See apt-secure(8) manpage for repository creation and user configuration details.
> E: Failed to fetch http://extras.ubuntu.com/ubuntu/dists/xenial/main/source/Sources  404  Not Found [IP: 91.189.92.152 80]
> E: Some index files failed to download. They have been ignored, or old ones used instead.

extras.ubuntu.com was retired in the Ubuntu 15.04 cycle:

  https://lists.ubuntu.com/archives/technical-board/2015-January/002063.html

Just remove it from sources.list.

-- 
Colin Watson                                       [cjwatson at ubuntu.com]