debian 10 apt安装不了软件

用debos构建了debian10的文件系统，在用apt-get 安装软件的时候出现如下错误

Err:1 https://mirrors.ustc.edu.cn/debian buster/main armhf libpci3 armhf 1:3.5.2-1
  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: 202.141.176.110 443]
Err:2 https://mirrors.ustc.edu.cn/debian buster/main armhf pciutils armhf 1:3.5.2-1
  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: 202.141.176.110 443]
E: Failed to fetch https://mirrors.ustc.edu.cn/debian/pool/main/p/pciutils/libpci3_3.5.2-1_armhf.deb  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: 202.141.176.110 443]
E: Failed to fetch https://mirrors.ustc.edu.cn/debian/pool/main/p/pciutils/pciutils_3.5.2-1_armhf.deb  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: 202.141.176.110 443]
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing

根据提示运行apt-get update,出现如下错误

Ign:1 https://mirrors.ustc.edu.cn/debian buster InRelease
Err:2 https://mirrors.ustc.edu.cn/debian buster 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: 202.141.176.110 443]
Reading package lists... Done                          
E: The repository 'https://mirrors.ustc.edu.cn/debian buster Release' no longer has 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.

分析是证书错误不可用，看了下系统时间，是2019年的，慢了一年多，于是用ntpdate更新下系统时间

$ ntpdate 公司对时服务器IP

重新使用apt-get install 安装软件，可以正常安装，问题解决。