shing@shing-K55A:~$ sudo apt update
[sudo] password for shing:
Get:1 http://security.ubuntu.com/ubuntu zesty-security InRelease [89.2 kB]
Hit:2 http://us.archive.ubuntu.com/ubuntu zesty InRelease
Get:3 http://us.archive.ubuntu.com/ubuntu zesty-updates InRelease [89.2 kB]
Ign:4 http://ppa.launchpad.net/kirillshkrogalev/ffmpeg-next/ubuntu zesty InRelease
Ign:5 http://ppa.launchpad.net/kubuntu-ppa/backports/ubuntu zesty InRelease
Hit:6 https://dl.winehq.org/wine-builds/ubuntu zesty InRelease
Hit:7 http://us.archive.ubuntu.com/ubuntu zesty-backports InRelease
Hit:8 http://ppa.launchpad.net/obsproject/obs-studio/ubuntu zesty InRelease
Err:9 http://ppa.launchpad.net/kirillshkrogalev/ffmpeg-next/ubuntu zesty Release
404 Not Found
Err:10 http://ppa.launchpad.net/kubuntu-ppa/backports/ubuntu zesty Release
404 Not Found
Get:11 https://repo.skype.com/deb stable InRelease [4,486 B]
Err:11 https://repo.skype.com/deb stable InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 1F3045A5DF7587C3
Reading package lists... Done
E: The repository 'http://ppa.launchpad.net/kirillshkrogalev/ffmpeg-next/ubuntu zesty Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://ppa.launchpad.net/kubuntu-ppa/backports/ubuntu zesty Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: https://repo.skype.com/deb stable InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 1F3045A5DF7587C3
E: The repository 'https://repo.skype.com/deb stable InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.