ubuntu自带的软件源连接太慢，改用国产的阿里软件源。修改/etc/apt/sources.list文件，添加阿里源debhttp://mirrors.aliyun.com/ubuntu/bionicmainrestricteduniversemultiversedebhttp://mirrors.aliyun.com/ubuntu/bionic-securitymainrestricteduniversemultiversedebhttp://mirrors.aliyun.com/ubuntu/bionic-updatesmainrestricteduniversemultiversedebhttp://mirrors.aliyun.com/ubuntu/bionic-proposedmainrestricteduniversemultiversedebhttp://mirrors.aliyun.com/ubuntu/bionic-backportsmainrestricteduniversemultiversedeb-srchttp://mirrors.aliyun.com/ubuntu/bionicmainrestricteduniversemultiversedeb-srchttp://mirrors.aliyun.com/ubuntu/bionic-securitymainrestricteduniversemultiversedeb-srchttp://mirrors.aliyun.com/ubuntu/bionic-updatesmainrestricteduniversemultiversedeb-srchttp://mirrors.aliyun.com/ubuntu/bionic-proposedmainrestricteduniversemultiversedeb-srchttp://mirrors.aliyun.com/ubuntu/bionic-backportsmainrestricteduniversemultiverse保存后执行apt-get更新apt-get升级
