昨天装系统装出问题了，今天又发现服务器内存条烧了一根，让本就不富裕的内存又-8G。今天好不容易装好了系统，发现
apt update又出现了问题。经过百度之后，摸索着解决了问题。本来想发个博客，又想起来服务器刚装好系统，啥都没有，没法发博客。
报错信息
violettec@linux:~# sudo apt-get update Ign:1 https://mirrors.ustc.edu.cn/ubuntu bionic InRelease Ign:2 https://mirrors.ustc.edu.cn/ubuntu bionic-updates InRelease Ign:3 https://mirrors.ustc.edu.cn/ubuntu bionic-backports InRelease Ign:4 https://mirrors.ustc.edu.cn/ubuntu bionic-security InRelease Ign:5 https://mirrors.ustc.edu.cn/ubuntu bionic-proposed InRelease Err:6 https://mirrors.ustc.edu.cn/ubuntu bionic Release Certificate verification failed: The certificate is NOT trusted. The certificate chain uses not yet valid certificate. Could not handshake: Error in the certificate verification. [IP: 202.141.160.110 443] Err:7 https://mirrors.ustc.edu.cn/ubuntu bionic-updates Release Certificate verification failed: The certificate is NOT trusted. The certificate chain uses not yet valid certificate. Could not handshake: Error in the certificate verification. [IP: 202.141.160.110 443] Err:8 https://mirrors.ustc.edu.cn/ubuntu bionic-backports Release Certificate verification failed: The certificate is NOT trusted. The certificate chain uses not yet valid certificate. Could not handshake: Error in the certificate verification. [IP: 202.141.160.110 443] Err:9 https://mirrors.ustc.edu.cn/ubuntu bionic-security Release Certificate verification failed: The certificate is NOT trusted. The certificate chain uses not yet valid certificate. Could not handshake: Error in the certificate verification. [IP: 202.141.160.110 443] Err:10 https://mirrors.ustc.edu.cn/ubuntu bionic-proposed Release Certificate verification failed: The certificate is NOT trusted. The certificate chain uses not yet valid certificate. Could not handshake: Error in the certificate verification. [IP: 202.141.160.110 443] Reading package lists... Done E: The repository 'https://mirrors.ustc.edu.cn/ubuntu bionic 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 'https://mirrors.ustc.edu.cn/ubuntu bionic-updates 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 'https://mirrors.ustc.edu.cn/ubuntu bionic-backports 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 'https://mirrors.ustc.edu.cn/ubuntu bionic-security 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 'https://mirrors.ustc.edu.cn/ubuntu bionic-proposed 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.
上面的报错信息，是我使用了中科大的源后，更新apt后的报错信息。当我复制下面这一段信息进行百度的时候，发现没有什么有用的线索。
E: The repository 'https://mirrors.ustc.edu.cn/ubuntu bionic 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.
当我尝试搜索靠上点的报错时：
Certificate verification failed: The certificate is NOT trusted. The certificate chain uses not yet valid certificate. Could not handshake: Error in the certificate verification.
发现也许是服务器时间错误，导致证书检验错误。我看了一下服务器时间：
violettec@linux:~# date -R Sun, 28 Jan 2018 15:59:44 +0000
（当时北京时间：2021/02/07 22:54）
本想用工具自动联网修改一下时间，想起来了apt是坏的，只能手动修改了。
violettec@linux:~# timedatectl set-timezone "Asia/Shanghai" #设置时区 violettec@linux:~# sudo date -s "2021-02-07 22:54:00" #设置时间
然后再apt update，换回清华源，终于正常了。
博客终于恢复了...