启动Alluxio：Could not create ServerSocket on address /0.0.0.0:19998

按照alluxio官网的单机或者集群安装教程，在进行
bin/alluxio format时出现错误：
question1：

[localhost] Exception in thread "main" java.lang.UnsupportedClassVersionError: alluxio/cli/Format : Unsupported major.minor version 51.0
[localhost] at java.lang.ClassLoader.defineClass1(Native Method)
[localhost] at java.lang.ClassLoader.defineClass(ClassLoader.java:634)
[localhost] at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
[localhost] at java.net.URLClassLoader.defineClass(URLClassLoader.java:277)
[localhost] at java.net.URLClassLoader.access$000(URLClassLoader.java:73)
[localhost] at java.net.URLClassLoader$1.run(URLClassLoader.java:212)
[localhost] at java.security.AccessController.doPrivileged(Native Method)
[localhost] at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
[localhost] at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
[localhost] at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
[localhost] at java.lang.ClassLoader.loadClass(ClassLoader.java:266)

在stackoverflow查看后，说是编译程序在高版本的java,但是运行在了较低版本，所以出现了版本不支持情况。然后查了所使用的测试机，java -version显示已是java1.8.
最后决定使用maven自行编译，在pom.xml中修改<hadoop.version>版本后，在jdk7的环境中执行mvn clean package -DskipTests 。问题解决。【1.8环境编译成功但是无法启动，a bug???】

question2：

[node2] Formatting Alluxio Worker @ node2
[node2] Exception in thread "main" java.lang.NoClassDefFoundError: alluxio/cli/Format
[node2] Caused by: java.lang.ClassNotFoundException: alluxio.cli.Format
[node2] at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
[node2] at java.security.AccessController.doPrivileged(Native Method)
[node2] at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
[node2] at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
[node2] at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
[node2] at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
[node2] Could not find the main class: alluxio.cli.Format. Program will exit.
[node2] Connection to node2 closed.

bin/alluxio-start.sh local之后发现是以下问题

Could not create ServerSocket on address /0.0.0.0:19998.

在alluxio-1.4.0/conf/alluxio-site.properties中增加配置项

export alluxio.master.port=18998
export alluxio.master.web.port=18999

然后重新执行bin/alluxio-start.sh local即可发现系统启动成功