ubuntu安装update出错，什么原因

很高兴为您解答：

Ubuntu 11 04 (Natty) 已经停止支持,但可以使用old-releases源了,先备份源列表文件:
sudo cp /etc/apt/sources list /etc/apt/sources list backup

sudo gedit /etc/apt/sources list
把里面的内容替换为以下内容:
deb old-releases ubuntu com/ubuntu/ natty main restricted universe multiverse
deb old-releases ubuntu com/ubuntu/ natty-security main restricted universe multiverse
deb old-releases ubuntu com/ubuntu/ natty-updates main restricted universe multiverse
deb old-releases ubuntu com/ubuntu/ natty-proposed main restricted universe multiverse
deb old-releases ubuntu com/ubuntu/ natty-backports main restricted universe multiverse
deb-src old-releases ubuntu com/ubuntu/ natty main restricted universe multiverse
deb-src old-releases ubuntu com/ubuntu/ natty-security main restricted universe multiverse
deb-src old-releases ubuntu com/ubuntu/ natty-updates main restricted universe multiverse
deb-src old-releases ubuntu com/ubuntu/ natty-proposed main restricted universe multiverse
deb-src old-releases ubuntu com/ubuntu/ natty-backports main restricted universe multiverse

重载源列表,使配置生效:
sudo apt-get update

安装SSH服务器和客户端:
sudo apt-get install openssh-server openssh-client