faisal:~$ sudo apt-get update
Hit:1 http://repo.steampowered.com/steam precise InRelease
Hit:2 http://archive.canonical.com/ubuntu xenial InRelease
Hit:3 http://ubuntu.mirrors.uk2.net/ubuntu xenial InRelease
Get:4 http://ubuntu.mirrors.uk2.net/ubuntu xenial-updates InRelease [95.7 kB]
Hit:5 http://ubuntu.mirrors.uk2.net/ubuntu xenial-backports InRelease
Hit:6 http://ubuntu.mirrors.uk2.net/ubuntu xenial-security InRelease
Get:7 http://ubuntu.mirrors.uk2.net/ubuntu xenial-updates/universe amd64 Packages [324 kB]
Get:8 http://ubuntu.mirrors.uk2.net/ubuntu xenial-updates/universe i386 Packages [321 kB]
Ign:9 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial InRelease
Hit:10 http://ppa.launchpad.net/flexiondotorg/hal-flash/ubuntu xenial InRelease
Hit:11 http://ppa.launchpad.net/geary-team/releases/ubuntu xenial InRelease
Hit:12 http://ppa.launchpad.net/linrunner/thinkpad-extras/ubuntu xenial InRelease
Hit:13 http://ppa.launchpad.net/numix/ppa/ubuntu xenial InRelease
Hit:14 http://ppa.launchpad.net/snwh/pulp/ubuntu xenial InRelease
Ign:15 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial Release
Ign:16 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main amd64 Packages
Ign:17 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main i386 Packages
Ign:18 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main all Packages
Ign:19 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main Translation-en_US
Ign:20 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main Translation-en
Ign:16 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main amd64 Packages
Ign:17 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main i386 Packages
Ign:18 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main all Packages
Ign:19 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main Translation-en_US
Ign:20 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main Translation-en
Ign:16 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main amd64 Packages
Ign:17 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main i386 Packages
Ign:18 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main all Packages
Ign:19 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main Translation-en_US
Ign:20 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main Translation-en
Ign:16 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main amd64 Packages
Ign:17 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main i386 Packages
Ign:18 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main all Packages
Ign:19 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main Translation-en_US
Ign:20 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main Translation-en
Ign:16 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main amd64 Packages
Ign:17 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main i386 Packages
Ign:18 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main all Packages
Ign:19 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main Translation-en_US
Ign:20 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main Translation-en
Err:16 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main amd64 Packages
404 Not Found
Ign:17 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main i386 Packages
Ign:18 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main all Packages
Ign:19 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main Translation-en_US
Ign:20 http://ppa.launchpad.net/caffeine-developers/ppa/ubuntu xenial/main Translation-en
Fetched 740 kB in 26s (27.5 kB/s)
Reading package lists... Done
W: The repository 'http://ppa.launchpad.net/caffeine-developers/ppa/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/caffeine-developers/ppa/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.
faisal:~$