由前一篇文章開始折騰supervisor，想玩玩tomcat異常退出後使用supervisor自動讓tomcat重新啓動，
隨即丟了一個tomcat在服務器裏面，本來就沒有放任何項目，空跑在那邊，只是tomcat有個界面就看看起沒起來。
於是手動停止tomcat的進程觸發supervisor自動拉起服務，應該是沒有問題的，但是，來來回回啓動了個兩三次，突然發現，tomcat竟然起不來了！
隨即查閱下日誌：
root@test-s1 bin]# tail -f ../logs/catalina.out
19-Jun-2018 15:57:06.666 INFO [main] org.apache.coyote.AbstractProtocol.init Initializing ProtocolHandler ["ajp-nio-8009"]
19-Jun-2018 15:57:06.667 INFO [main] org.apache.tomcat.util.net.NioSelectorPool.getSharedSelector Using a shared selector for servlet write/read
19-Jun-2018 15:57:06.667 INFO [main] org.apache.catalina.startup.Catalina.load Initialization processed in 535 ms
19-Jun-2018 15:57:06.684 INFO [main] org.apache.catalina.core.StandardService.startInternal Starting service Catalina
19-Jun-2018 15:57:06.684 INFO [main] org.apache.catalina.core.StandardEngine.startInternal Starting Servlet Engine: Apache Tomcat/8.1.15
19-Jun-2018 15:57:06.690 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory /opt/apache-tomcat-8.1.15-server/webapps/ROOT
卡在這個啓動狀態至少由10分鐘才能完全啓動起來，而且每次都這樣。。。空跑都能這麼操蛋？部署個項目還得了？難道要半小時？
網上查閱到有個大神寫的文章，大意就是下面這句話：
The library used for random number generation in Sun's JVM relies on /dev/random by default for UNIX platforms. This can potentially block the Oracle WebLogic Communication Services process because on some operating systems /dev/random waits for a certain amount of "noise" to be generated on the host machine before returning a result. Although /dev/random is more secure, Oracle recommends using /dev/urandom if the default JVM configuration delays Oracle WebLogic Communication Services startup.
To determine if your operating system exhibits this behavior, try displaying a portion of the file from a shell prompt:
head -n 1 /dev/random
Open the $JAVA_HOME/jre/lib/security/java.security file in a text editor.
Change the line:
securerandom.source=file:/dev/random
to read:
securerandom.source=file:/dev/urandom
Save your change and exit the text editor.
就是linux提供隨機數設備是/dev/random 和/dev/urandom，一般我們都只是都使用"/dev/random"，這個參數做隨機數（因爲每本操蛋的書都是這麼寫的！也沒人說過爲啥。）
兩個有區別，urandom安全性沒有random高，但random需要時間間隔生成隨機數。jdk默認調用random。
所以根據上面的說法，修改配置文件：
find / -name securerandom.source
找到Java.security文件，在文件中找到securerandom.source這個設置項，將其改爲：
securerandom.source=file:/dev/urandom
修改完畢後，重啓tomcat，瞬間啓動完畢。