I have a Java server running on an Ubuntu machine and every few days it just... dies. Every exit point on every thread leaves a log entry and everything is wrapped in try-catch with a log entry in the catch, but on these mysterious shutdowns, nothing gets logged.
I launch the server with a simple nohup java -jar MyServer.jar command.
One time, I had a terminal I launched it from still open when this happened and the word "KILLED" showed up there. Note that, when I kill the server myself with a kill command from another terminal, nothing shows up.
How do I determine what killed it?
Related
I'm developing a Java desktop application for Windows and I'm trying to implement the Windows Restart Manager. I'm successfully receiving the Windows messages for exiting the application and when I send them manually, it just works and the application shut downs.
When I do it as part of the uninstall process, the shutdown procedure in my application runs and I can even see it calls System.exit(0) but even after that, there's a process that doesn't stop. My Java application is packaged into an executable file using launch4j in case that's relevant.
The way I know System.exit(0) is being called is because I'm dumping debugging information to a file and I print out that System.exit(0) is about to be call and I can see that whether the application succeeds or fails on properly shutting down.
Using the Process Explorer I can see the javaw.exe sub-process and when the exit procedure happens, that goes away, but the parent process remains. While the is running, it looks like this:
and after the failed exit, it looks like this:
If I have a remote debugger connected to the process, at this point, the debugger gets disconnected.
What could be causing this?
I'm close to being convinced this is a bug in launch4j, so, I reported it here: https://sourceforge.net/p/launch4j/bugs/185/
I have a .jar runnable running on my server. When I run the file locally I am able to see its output via my IDE. Similarly I can connect via SSH and run the file and see the output, but when I close the session the JAR exits.
Is there any way to have my application continuously running and then tapping into the java applications output using a terminal service like SSH without having to stop/start the application.
Any help would be appreciated.
You can use either screen or nohup
What is happening is that when you close your SSH session, there is a hangup call made to the program.
You could use nohup. Nohup stands for "no hangup"
nohup java -jar myJar.jar > outputFile.txt
That would run the program in the backround and send all output to outputFile.txt. When you end your session it will continue running. You must use a kill command to kill it.
The second option is you could use screen which essentually creates a detachable "ghost session". When you run screen it looks like you are in a different ssh session. Then when you detach from screen, the processes continues in the backround. When you exit your ssh session, screen continues to run.
You simply ssh back into the server, and re-attach to your screen session, and like magic, your program is still running with all relevent output. A simple read on the man page should catch you up on how to do this.
man screen
Lastly, I decided to add this third option, not because its viable, but simply so you can understand that it is an option. (Some people would claim this is the only REAL option as it is what your SUPPOSED to do. Frankly I couldn't care less and think you should do whatever is the easiest to get to your goal.)
You can also edit your program to swallow the hangup signal. The program would then always run in the backround. You can then use
java -jar myJar.jar & > outputFile.com
The & tells the command to start a new process (aka run in the backround) and the > sends the output to a file. This is how normal server applications like tomcat or spring boot work. They simply swallow the hangup call.
I have a small java server listening on port 10299 for performing some image processing on demand. I start the program as follows:
java -Xms15m -Xmx25m -jar /tools/image-server.jar > /tools/image-server.log &
After an indeterminate period of time the process gets killed whithout any error message (or at least i haven't discovered any...). The OS is Ubuntu 10.04.3 LTS.
The code itself seems to be working fine, since it is running without error on my other machine.
What could cause the unexpected ending of the program?
Is it possible to check which process killed the program?
Which log files could I check?
I am writing a java program that runs under unix.
It would like run forever. But when I start it from command line, I have to leave that window open always until the program stop.
Could anyone give me some idea about how can i run it at back end? Just start it from command line then I could close that command line.
Thank you very much.
If you don't want to "daemonize" it you can just use nohup:
$ nohup your-program &
$ exit
and your-program will continue to run in the background until it finishes.
You're asking about making your program a "daemon". Check out these links about daemonizing java programs, and this one about daemonizing any process in linux.
...Another option is to use the "screen" utility. Its a little tricky if you've never used it, but you can do things like launch a job in a terminal at work and easily reconnect to the same terminal from anywhere else to check on the status of the job. I use it for connecting to servers where I run long-running jobs. Without using screen my process would die if my local machine crashes, or the power goes out, or fire, etc.
I have a Java application launched via Webstart. About half the time, this program will not die. This program listens on a socket and when it receives a particular command, should close down. When it receives this command, it prints out what it normally should to the java console (that it received the shutdown command), the Java console closes, all the windows close, but the java process continues to run.
I have tried switching System.exit(0) to Runtime.getRuntime().halt(0) with no success - the same problem happens (my initial thought was a shutdown hook was affecting it).
Furthermore, when I have VisualVM connected to the Java process, it also indicates that it loses the connection when halt or exit are called, and I cannot reconnect, but the java process continues to exist.
Any ideas on how I could solve this? I've tries wrapping the program in try { } and exit/halt in finally { } to ensure nothing was holding it up, tried halting instead of exiting, etc...
My only thought is Java could be retaining a system resource (file handle to socket or something) or be stuck in a system call so the system won't let it quit - but the Java console closes, which to me seems like an indication the VM is trying to shutdown...
Any thoughts or ideas are appreciated!