当我尝试更新我的Ubuntu 16.04。我已经尝试了几种解决方案，但目前都没有效果。
错误：
W: http://archive.canonical.com/ubuntu/dists/precise/Release.gpg: Signature by key 630239CC130E1A7FD81A27B140976EAF437D05B5 uses weak digest algorithm (SHA1)
W: http://us.archive.ubuntu.com/ubuntu/dists/precise-security/InRelease: Signature by key 630239CC130E1A7FD81A27B140976EAF437D05B5 uses weak digest algorithm (SHA1)
W: GPG error: http://extras.ubuntu.com/ubuntu precise Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 16126D3A3E5C1192
W: The repository 'http://extras.ubuntu.com/ubuntu precise Release' 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.
W: http://us.archive.ubuntu.com/ubuntu/dists/precise-updates/InRelease: Signature by key 630239CC130E1A7FD81A27B140976EAF437D05B5 uses weak digest algorithm (SHA1)
W: http://us.archive.ubuntu.com/ubuntu/dists/precise-backports/InRelease: Signature by key 630239CC130E1A7FD81A27B140976EAF437D05B5 uses weak digest algorithm (SHA1)
W: http://us.archive.ubuntu.com/ubuntu/dists/precise/Release.gpg: Signature by key 630239CC130E1A7FD81A27B140976EAF437D05B5 uses weak digest algorithm (SHA1)
W: The repository 'http://ppa.launchpad.net/upubuntu-com/network/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/upubuntu-com/network/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.
取消勾选一些不需要的包/存储库后从软件和更新部分，我设法摆脱了一些错误，但仍然存在一些错误：
The repository 'http://ppa.launchpad.net/upubuntu-com/network/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: http://archive.canonical.com/ubuntu/dists/precise/Release.gpg: Signature by key 630239CC130E1A7FD81A27B140976EAF437D05B5 uses weak digest algorithm (SHA1)
E: Failed to fetch http://ppa.launchpad.net/upubuntu-com/network/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.
涂抹溶液后提供如下（由 Raphael 提供），大多数错误都已解决。除了这些错误：
W: The repository 'http://ppa.launchpad.net/upubuntu-com/network/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/upubuntu-com/network/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.
答案1
您正在使用Xenial，但您的sources.list包含 的链接Precise。要纠正此问题，
备份您当前的
sources.list：sudo mv /etc/apt/sources.list /etc/apt/sources.list.bak创建一个新的
source.list：sudo nano /etc/apt/sources.list复制并粘贴以下内容：
deb http://us.archive.ubuntu.com/ubuntu/ xenial main restricted universe multiverse deb-src http://us.archive.ubuntu.com/ubuntu/ xenial main restricted universe multiverse deb http://us.archive.ubuntu.com/ubuntu/ xenial-security main restricted universe multiverse deb http://us.archive.ubuntu.com/ubuntu/ xenial-updates main restricted universe multiverse deb http://us.archive.ubuntu.com/ubuntu/ xenial-proposed main restricted universe multiverse deb http://us.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse deb-src http://us.archive.ubuntu.com/ubuntu/ xenial-security main restricted universe multiverse deb-src http://us.archive.ubuntu.com/ubuntu/ xenial-updates main restricted universe multiverse deb-src http://us.archive.ubuntu.com/ubuntu/ xenial-proposed main restricted universe multiverse deb-src http://us.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse然后，在键盘上按下以下内容：
Ctrl+X然后Y，最后Enter。
最后，尝试更新您的来源：
sudo apt-get update
编辑:-ppa错误就是它所说的。它ppa没有 的发布文件Xenial。要删除ppas，请按照以下答案操作询问Ubuntu。