我对 Ubuntu 完全不了解，只在办公室电脑上使用它。
以下是我发布的版本的详细信息：
Distributor ID: Ubuntu
Description: Ubuntu 16.04.3 LTS
Release: 16.04
Codename: xenial
在过去的 6-9 个月里，我使用它没有遇到任何问题。我习惯每周左右更新一次系统（sudo apt-get update、sudo apt-get upgrade 和 sudo apt-get dist-upgrade），直到大约 2 周前，一切似乎都运行正常。
然而，在过去的两周里，运行这些命令开始返回大量错误。我的 LibreOffice 也损坏了，我卸载了它并安装了一个干净的版本，但令我震惊的是，我也无法安装新版本。我关注了这里的很多帖子并做了十几件事，我担心这会加剧我的问题。我尝试更改服务器等，在此过程中，我的软件和更新完全停止工作。
只有我的 Synaptic 包管理器和当我尝试重新加载包时它也会返回以下错误。
这是我在 Synaptic 包管理器中收到的消息。
The repository 'http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial Release' does not have a Release file.
Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
See apt-secure(8) manpage for repository creation and user configuration details.
Failed to fetch http://ppa.launchpad.net/shutter/ppa/ubuntu/dists/xenial/InRelease Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
Failed to fetch http://ppa.launchpad.net/teejee2008/ppa/ubuntu/dists/xenial/InRelease Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
Failed to fetch http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu/dists/xenial/main/binary-amd64/Packages 404 Not Found
Some index files failed to download. They have been ignored, or old ones used instead.
这些是我的 sources.list 的内容
#------------------------------------------------------------------------------#
# OFFICIAL UBUNTU REPOS #
#------------------------------------------------------------------------------#
###### Ubuntu Main Repos
deb http://in.archive.ubuntu.com/ubuntu/ xenial main restricted universe multiverse
deb-src http://in.archive.ubuntu.com/ubuntu/ xenial main restricted universe multiverse
###### Ubuntu Update Repos
deb http://in.archive.ubuntu.com/ubuntu/ xenial-security main restricted universe multiverse
deb http://in.archive.ubuntu.com/ubuntu/ xenial-updates main restricted universe multiverse
deb-src http://in.archive.ubuntu.com/ubuntu/ xenial-security main restricted universe multiverse
deb-src http://in.archive.ubuntu.com/ubuntu/ xenial-updates main restricted universe multiverse
sudo apt-get 更新
Ign:1 http://dl.google.com/linux/chrome/deb stable InRelease
Hit:2 http://dl.google.com/linux/chrome/deb stable Release
Hit:3 http://in.archive.ubuntu.com/ubuntu xenial InRelease
Hit:5 http://in.archive.ubuntu.com/ubuntu xenial-security InRelease
Hit:6 http://ppa.launchpad.net/apt-fast/stable/ubuntu xenial InRelease
Hit:7 http://in.archive.ubuntu.com/ubuntu xenial-updates InRelease
Ign:8 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial InRelease
Hit:9 http://ppa.launchpad.net/libreoffice/ppa/ubuntu xenial InRelease
Hit:10 http://ppa.launchpad.net/mc3man/xerus-media/ubuntu xenial InRelease
Hit:11 http://ppa.launchpad.net/nemh/systemback/ubuntu xenial InRelease
Get:12 http://ppa.launchpad.net/shutter/ppa/ubuntu xenial InRelease [1,005 B]
Err:12 http://ppa.launchpad.net/shutter/ppa/ubuntu xenial InRelease
Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
Get:13 http://ppa.launchpad.net/teejee2008/ppa/ubuntu xenial InRelease [1,005 B]
Err:13 http://ppa.launchpad.net/teejee2008/ppa/ubuntu xenial InRelease
Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
Ign:14 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial Release
Ign:15 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main amd64 Packages
Ign:16 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main i386 Packages
Ign:17 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main all Packages
Ign:18 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main Translation-en_IN
Ign:19 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main Translation-en
Ign:15 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main amd64 Packages
Ign:16 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main i386 Packages
Ign:17 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main all Packages
Ign:18 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main Translation-en_IN
Ign:19 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main Translation-en
Ign:15 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main amd64 Packages
Ign:16 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main i386 Packages
Ign:17 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main all Packages
Ign:18 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main Translation-en_IN
Ign:19 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main Translation-en
Ign:15 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main amd64 Packages
Ign:16 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main i386 Packages
Ign:17 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main all Packages
Ign:18 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main Translation-en_IN
Ign:19 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main Translation-en
Ign:15 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main amd64 Packages
Ign:16 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main i386 Packages
Ign:17 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main all Packages
Ign:18 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main Translation-en_IN
Ign:19 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main Translation-en
Err:15 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main amd64 Packages
404 Not Found
Ign:16 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main i386 Packages
Ign:17 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main all Packages
Ign:18 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main Translation-en_IN
Ign:19 http://ppa.launchpad.net/fossfreedom/packagefixes/ubuntu xenial/main Translation-en
Fetched 2,010 B in 42s (47 B/s)
Reading package lists... Done
W: The repository 'http://ppa.launchpad.net/fossfreedom/packagefixes/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/shutter/ppa/ubuntu/dists/xenial/InRelease Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
E: Failed to fetch http://ppa.launchpad.net/teejee2008/ppa/ubuntu/dists/xenial/InRelease Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
E: Failed to fetch http://ppa.launchpad.net/fossfreedom/packagefixes/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.