问题
I have no knowledge on Linux commands but I couldn't resist asking why such errors are showing after the command sudo apt-get update:
W: The repository 'http://ppa.launchpad.net/bumblebee/stable/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/ubuntu-x-swat/x-updates/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: GPG error: http://ppa.launchpad.net/umang/indicator-stickynotes/ubuntu xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 799A5FD5D1C5997F
W: The repository 'http://ppa.launchpad.net/umang/indicator-stickynotes/ubuntu xenial InRelease' is not signed.
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/bumblebee/stable/ubuntu/dists/xenial/main/binary-amd64/Packages 404 Not Found
E: Failed to fetch http://ppa.launchpad.net/ubuntu-x-swat/x-updates/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 would like to know what's exactly going on with the following errors. An explanation would be very helpful for me.
回答1:
I solved this error following theses steps:
Open the Software Updates application; - In "Other Software" tab unmark all options; - In Ubuntu Software tab, "Download from:" choose "Main server" option.
Click in "Close" button and wait a minute until ubuntu reload apt-get.
Done.
回答2:
I solved this error following theses steps:
1. Open the Software Updates application;
2. In "Other Software" tab unmark all options;
3. In Ubuntu Software tab, "Download from:" choose "Main server" option.
4. Click in "Close" button and wait a minute until ubuntu reload apt-get.
Done.
回答3:
The following commands will resolve the issue,
wget -q "http://deb.playonlinux.com/public.gpg" -O - | sudo apt-key add -
sudo wget http://deb.playonlinux.com/playonlinux_trusty.list -O /etc/apt/sources.list.d/playonlinux.list
sudo sh -c "echo 'deb http://download.opensuse.org/repositories/home:/strycore/xUbuntu_16.04/ /' > /etc/apt/sources.list.d/lutris.list"
wget -nv https://download.opensuse.org/repositories/home:strycore/xUbuntu_16.04/Release.key -O Release.key
sudo apt-key add - < Release.key
sudo apt-get update
来源：https://stackoverflow.com/questions/41244349/getting-following-error-after-the-commad-sudo-apt-get-update-on-ubuntu-16-04