这些路径很多只是个链接而已，采用ls -l可以一层一层查看到真实路径的：
[roysong@roysong ~]$ ls -l /usr/bin/java
lrwxrwxrwx 1 root root 22 Mar 8 08:51 /usr/bin/java -> /etc/alternatives/java
[roysong@roysong ~]$ ls -l /etc/alternatives/java
lrwxrwxrwx 1 root root 46 Mar 8 08:51 /etc/alternatives/java -> /usr/lib/jvm/jre-1.7.0-openjdk.x86_64/bin/java
[roysong@roysong ~]$ ls -l /usr/lib/jvm/jre-1.7.0-openjdk.x86_64/bin/java
-rwxr-xr-x 1 root root 10048 Mar 5 14:46 /usr/lib/jvm/jre-1.7.0-openjdk.x86_64/bin/java
