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.
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'm using JSch to automate remotely launching a python script from a background Java process.
Modifying the Shell.java example included in the JSch package, I've successfully installed JSch, connected to my Pi, and even commented out the user/domain/password/host key checking prompt boxes in favor of storing these values directly in my Java code.
After my java code logs into the remote Pi, I'd like it to send something like
sudo nohup python2 myFoo.py & disown
to the terminal.
In the Shell.java example I'm modifying, I see lines of code redirecting the input and output streams of the channel object to System.in and System.out but I'd like to simply manually inject that above line into the remote terminal and disconnect.
Why/my goal:
I have a small mesh network of Pi's running a script for most of the day.
I'd like to eliminate downtime, but the code sometimes stops working after looping for 3-4 days straight, (sometimes as long as a week straight before the code bugs out and stops).
The script running on each node updates a mySQL database with a "last check in" field.
I'm hoping to write a small background program in Java that will run indefinitely on my server, checking the "last check in" for each station every now and then, and if it notices a node go down, remotely ssh into it and sudo reboot now, wait about 60-100 seconds, then sudo nohup python2 myFoo.py & disown
You have picked a wrong example. The "shell" channel is for implementing an interactive shell session, not for automating a command execution.
Use the "exec" channel, see the Exec.java example.
Channel channel=session.openChannel("exec");
((ChannelExec)channel).setCommand(command);
channel.connect();
...
For a full code, see How to read JSch command output? – Which shows how to correctly read both standard and error output simultaneously, to allow command to complete and to collect all output including the errors.
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?
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 open up an external application from my java application. How can I close this application from the same Java application?
thanks
The best you can do (without venturing into messy/complicated/platform specific stuff) is to call Process.kill() on the Process object you got when you started the external application.
I don't think this is guaranteed to close the application*, and there is a chance that it may cause it to close uncleanly; i.e. without giving the application a chance to save open files, etc.
* Indeed, on *NIX if you started a "setuid root" process from a non-root Java application, and the OS won't let it send any signals to to.
Why don't you have a batch (Windows) or script (*nix) file that start and stops that application, and then run your runtime.exec with the parameter start/stop?
UPDATE:
This may help: http://it.toolbox.com/blogs/database-solutions/kill-a-process-in-windows-bat-19875
Second Update
You can also search by exe name using: 'tasklist ^| findstr /i excel.exe'
On Windows this will fail. It's a top 25 bug (or maybe top 25 rfe), though it really isn't so much Java's fault ... On Windows any children of the parent process will not be killed when parent is killed..... and there are many ways to run afoul of this (cmd /c anything and you will be in game-over-land)