Ubuntu 解决：当执行`sudo apt-get update`命令时 出现的 “apt-get 404 Not Found Package Repository Errors” 问题

Ubuntu 解决：当执行sudo apt-get update或者sudo apt-get install命令是出现的 “apt-get 404 Not Found Package Repository Errors” 问题 和 “E: Some index files failed to download They have been ignored, or old ones used” 问题

W: The repository ‘http://ppa.launchpad.net/ackondro/tibesti/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://ppa.launchpad.net/ackondro/tibesti/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.
E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable)
E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?

或者

W: The repository ‘http://ppa.launchpad.net/ackondro