1.
Open the terminal and use the system's built-in gedit editor to edit the sources file under administrator privileges.
su
//输入密码
//有需要的话提前备份
gedit /etc/apt/sources.list
2.
Replace the Tsinghua University mirror source (note that ubuntu is followed by -ports, and the x86 architecture does not have this suffix. I failed to select the wrong update source before): https://mirrors.tuna.tsinghua.edu. cn/help/ubuntu-ports/Select according to your system version, then copy and paste it, save and close.
3.
Use the apt-get package management tool to update the verification:
apt-get update//更新源
apt-get upgrade//更新已下载的包
If you are using the Debian series instead of the Redhat series, just replace apt-get with yum.