Note the use of the kill command in Java applications

 

Foreword

As we all know, kill is used to kill process linux system.

kill pid [..]

The kill command may be sent to the corresponding predetermined signal process or work. The default is to use the kill command signal 15 for the end of the process or work. If the process or working ignore this signal, you can use the signal 9, forced to kill the process or job.

Therefore, to ensure that the process to kill if you can use a -9 argument

kill -9 pid [..]

The use -3 parameters, you can print process execution log

kill -3 pid

Applications in Java

Create a web application of SpringBoot

Start classes are as follows, add a hook function, when the process closed, will call the hook function.

@SpringBootApplication
public class WebApplication {

    public static void main(String args[]){

        SpringApplication.run(WebApplication.class,args);

        Runtime.getRuntime().addShutdownHook(new Thread(){

            @Override
            public void run() {
                System.out.println("do ShutdownHook.......... ");
            }
        });
    }
}

 

 Use maven package.

mvn package

 

 

Testing kill -3　

Start the application

Be careful if you use relative paths to start applications, jps see the name of the process for the jar, using an absolute path follows the full jar name is displayed: web-1.0.jar.

java -jar ~/aProject/web/target/web-1.0.jar

 

View the process pid

lgj@lgj-Lenovo-G470:~/aProject/web/target$ jps | grep web
21060 web-1.0.jar

 

Use kill -3 

lgj@lgj-Lenovo-G470:~/aProject/web/target$ kill -3 21060

 

You can see the start screen printed stack information Java applications. Print signal is received -3 time thread information.

If you use the following way to start the application

nohup java -jar ~/aProject/web/target/web-1.0.jar   &

lgj@lgj-Lenovo-G470:~/aProject/web/target$ ls -l |grep nohup.out 
-rw------- 1 lgj lgj    22811 Jun  9 00:41 nohup.out

 

You can see the start of the directory where more than one file nohup.out. The document records the application process to start running log.

nohup command &;

Saying that he sets run applications.

At this time, using kill -3. Thread information can be printed to the nohup.out view.

Testing kill and kill -9

Start the application

java -jar ~/aProject/web/target/web-1.0.jar

 

Use kill the process kill pid

lgj@lgj-Lenovo-G470:~/aProject/web/target$ jps | grep web
21470 web-1.0.jar
lgj@lgj-Lenovo-G470:~/aProject/web/target$ kill 21470
lgj@lgj-Lenovo-G470:~/aProject/web/target$ 

 

You can see the output log output function hooks printed

do ShutdownHook.......... 

2019-06-09 01:18:28.610  INFO 21470 --- [           main] com.demo.web.WebApplication              : Started WebApplication in 4.585 seconds (JVM running for 5.274)
do ShutdownHook.......... 
2019-06-09 01:18:41.381  INFO 21470 --- [       Thread-3] o.s.s.concurrent.ThreadPoolTaskExecutor  : Shutting down ExecutorService 'applicationTaskExecutor'

 

Use kill -9 pid kill the process

lgj@lgj-Lenovo-G470:~/aProject/web/target$ jps | grep web
21568 web-1.0.jar
lgj@lgj-Lenovo-G470:~/aProject/web/target$ kill -9 21568

 

The last log does not output the contents of the hook function

2019-06-09 01:20:37.579  INFO 21568 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8452 (http) with context path ''
2019-06-09 01:20:37.585  INFO 21568 --- [           main] com.demo.web.WebApplication              : Started WebApplication in 4.171 seconds (JVM running for 4.812)
Killed

 

 

to sum up

When using the kill operation java application

1.kill -3 pid can print thread information of the current process, but does not close the Java application!

2.kill pid is kill -15 pid, will call the hook function ShutdownHook , general ShutdownHook will be some operations, such as saving data, close the connection.

3.kill -9 pid. Does not call the hook function ShutdownHook .