添加源时出错：
add-apt-repository ppa:qbittorrent-team/qbittorrent-stable
ERROR: '~qbittorrent-team' user or team does not exist.确认ppa用户名没错后用curl测试http获取是否正常，提示证书无效：
curl 'https://launchpad.net/~qbittorrent-team/+archive/ubuntu/qbittorrent-stable'
curl: (60) SSL certificate problem: certificate is not yet valid安装证书后再试：
apt-get install ca-certificates依旧出现错误，查看系统时间不对，通过ntp更新时间解决：
ntpdate ntp.ubuntu.com