"sudo apt-get update" >> Not update [closed]
*Purpose: Install "turtlebot" for kinetic(16.04) / (ROS book - Morgan Quigley, studying)
*My Development environment: Ubuntu 16.04 / ROS-kinetic / Notebook: xps 15 9570 / Multi-boot: Windows 10 (C drive) / Ubuntu (E drive) / ★ROS-kinetic / Rviz / gazebo /turtlebot3 >> already installed
*Ref Wiki http://wiki.ros.org/kinetic/Installat...
*Uniqueness - Server change Not updated >> changed "old-releases.ubuntu.com"
*Message ROS : https://imgur.com/a/JQeVZQg
*Error Message / Sever: http://old-releases.ubuntu.com/ubuntu
Err:11 http://ppa.launchpad.net/kirillshkrogalev/ffmpeg-next/ubuntu xenial/main amd64 Packages 404 Not Found
W: The repository 'http://old-releases.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.
W: The repository 'http://ppa.launchpad.net/kirillshkrogalev/ffmpeg-next/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://kr.archive.ubuntu.com/ubuntu/dists/xenial/InRelease Unable to find expected entry 'http://us.archive.ubuntu.com/ubuntu//source/Sources' in Release file (Wrong sources.list entry or malformed file)
E: Failed to fetch http://old-releases.ubuntu.com/ubuntu/dists/xenial/main/binary-amd64/Packages 404 Not Found [IP: 91.189.88.153 80]
E: Failed to fetch http://ppa.launchpad.net/kirillshkrogalev/ffmpeg-next/ubuntu/dists/xenial/main/binary-amd64/Packages 404 Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.
I don't see any errors from the ROS apt repo, but it looks like the other PPAs and apt repos that you have configured are not set up correctly or have been turned off since the last time you used this computer.
I had something similar, i think it has something to do with the GPG keys that have been changed. you could try this link
Are you running behind a proxy server? If so then:
1) Ensure proxy settings are correct in ~/.bashrc and /etc/apt/apt.conf
2) Run "source ~/.bashrc"
3) Run "sudo -E apt-get update"
gpg key: New Apply(already) C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654
and proxy server ---> Oh, no
This doesn't look like a problem with any of the ROS repositories, but as @ahendrix already comments, with other repositories.
As such, I'm going to close this question as off-topic for this site, and would recommend you @ik_Builder to post this on a forum such as Ask Ubuntu.