我知道已经添加了类似的问题，但它们对我来说都不起作用。
事情是这样的：
我正在寻找问题的解决方案，然后我申请了来自 nicktux 的解决方案
我是 Linux 新手，使用 Ubuntu 18.04。我可能盲目地输入了解决方案，但现在我遇到了更大的问题。
当我输入时sudo apt-get update我得到：
Reading package lists... Done
W: GPG error: http://archive.canonical.com/ubuntu precise Release: The following signatures were invalid: 630239CC130E1A7FD81A27B140976EAF437D05B5
E: The repository 'http://archive.canonical.com/ubuntu precise Release' 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.
W: GPG error: http://extras.ubuntu.com/ubuntu precise Release: The following signatures were invalid: C47415DFF48C09645B78609416126D3A3E5C1192
E: The repository 'http://extras.ubuntu.com/ubuntu precise Release' 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.
W: GPG error: http://us.archive.ubuntu.com/ubuntu precise-security InRelease: The following signatures were invalid: 630239CC130E1A7FD81A27B140976EAF437D05B5
（重复了相同的链接。）
我试过sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 630239CC130E1A7FD81A27B140976EAF437D05B5
什么都没用。我现在非常紧张，希望我不需要因为类似的问题再次格式化我的笔记本电脑。
告诉我我该怎么办？