2012-3-21
1.update-alternatives
参考网上帖子安装jdk时，都会有如下配置，但很少有解释command结尾的数字代表什么意思
。update-alternatives是uubuntu中专门维护系统链接符的工具。其中结尾数字是更改后的优先级。

sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/java-7-sun/bin/java 300  sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/java-7-sun/bin/javac 300

在这片博客中Install JDK 7 on Ubuntu，作者有这么两段段描述引用sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk1.7.0/jre/bin/java 3
to add your new JDK 7 installation into alternatives list. I put 3 there as 2 was last number for my configuration. You should use your own number from the previous step increased by 1.引用 sudo update-alternatives install /usr/bin/java java /usr/lib/jvm/jdk1.7.0/jre/bin/java 0

This will select needed java version in case you had not any previous java version installed before.所以这个数字不是一味的填写300。这片博客中也有提到。How do I install Oracle Java JDK 7?