注释掉 /etc/apt/apt.conf文件内容
# 查看当前代理:
env |grep https_proxy
env |grep http_proxy
# 去除当前代理
export https_proxy=
export http_proxy=
# 确定哪些网址不需要代理,一般是单位域名后缀
# 如果想永久使用,将该句增加到/etc/profile, 然后source /etc/profile
export no_proxy=.ustc.edu.cn
# 修改开源软件下载源,其中是开源软件镜像源地址
vi /etc/apt/sources.list
# 下载软件包
sudo apt update
# 升级软件包
sudo apt dist-upgrade
sudo apt-get autoremove
sudo apt install update-manager-core
sudo do-release-upgrade