Stop Java from killing Bash script that started it

I’ve spent the past couple days working on this, and at this point I am super stuck. I have a Java program that must be run not as a service. This program must also be capable of updating itself when a new file is given for updating.

As a result, I have a script that is started with Linux that starts the Java application and then checks every 5 seconds if the application has been terminated. If the application has been terminated, it should check if there is an update and then start appropriately.

This is the code for that script:

#!/bin/bash
JAVA_HOME=/usr/lib/jvm/java-16-openjdk-amd64
WORKING_DIR=~/Data
LOG=$WORKING_DIR/logs/Bash.log

rm $LOG
echo "Script started" > $LOG

while true; do
  source $WORKING_DIR/Server.pid

  if ! kill -0 $AppPID; then

    echo "App must be started" >> $LOG

    source $WORKING_DIR/UpdateStatus
    if [ "$UpdateReady" -eq "1" ]; then
      echo "Moving files for update" >> $LOG

      mv $WORKING_DIR/Server.jar $WORKING_DIR/old.jar
      mv $WORKING_DIR/new.jar $WORKING_DIR/Server.jar
    fi

    nohup ${JAVA_HOME}/bin/java -jar ${WORKING_DIR}/Server.jar &
    echo AppPID="$!" > $WORKING_DIR/Server.pid
    echo "Server started" >> $LOG

    if [ "$UpdateReady" -eq "1" ]; then
      echo "Checking for safe update" >> $LOG
      source $WORKING_DIR/Server.pid
      echo UpdateReady="0" > $WORKING_DIR/UpdateStatus

      sleep 5;

      if kill -0 $AppPID; then
        echo "Update successful" >> $LOG
        rm $WORKING_DIR/old.jar
      else
        echo "Update failed, restarting old jar" >> $LOG
        rm $WORKING_DIR/Server.jar
        mv $WORKING_DIR/old.jar $WORKING_DIR/Server.jar
        nohup ${JAVA_HOME}/bin/java -jar ${WORKING_DIR}/Server.jar &
        echo AppPID="$!" > $WORKING_DIR/Server.pid
      fi

    fi

    echo "Server start process finished, going into idle state" >> $LOG
  fi

  sleep 5
  echo "5 seconds idle passed" >> $LOG
done

To initialize the update, I have tried a couple of different things, both with the same result. First I had set UpdateReady="1" through Java, then used exit(0);. I have also tried having Java call a Bash script which also sets UpdateReady="1" but uses kill $AppPID to shutdown the java application.

The result is that both the Java application and the Bash script stop executing causing the update and restart to fail! I have looked through a significant amount of Stack Overflow questions and answers finding things such as nohup, all to no avail.

I will once again state that the Java application cannot be run as a service. No packages other than what is included in Java or made by Apache can be used, and no programs can be installed to Linux. I would prefer to solve the problem with Bash.

Upon testing some things mentioned in comments, I may have missed something that turns out to be important. While all other runs of the startup script will be run by the startup applications manager, the initial run is not.

The install is taken care of remotely with an SSH connection sending the following command string:

cd /home/UserName; unzip -u -o Server.zip; chmod 777 install.sh; bash install.sh &; exit

install.sh is as follows:

#!/bin/bash
INSTALL_DIR=~/Data

mkdir ${INSTALL_DIR}
mkdir ${INSTALL_DIR}/logs
mkdir ${INSTALL_DIR}/data

cp Server.jar ${INSTALL_DIR}/Server.jar
cp service-start.sh ${INSTALL_DIR}/service-start.sh

chmod 777 ${INSTALL_DIR}/service-start.sh

rm Server.jar
rm service-start.sh
rm Server.zip

nohup bash $INSTALL_DIR/service-start.sh &

Upon rebooting my machine, I noticed that this problem goes away! This means that there must be a problem with the initial setup script. When the shell command is run, it does seem to be sticky and not actually let go after the bash install.sh &. I have tried putting nohup at the beginning of this, however the entire line will not run in that case for reasons I am not able to determine.

I would prefer to not have the user be forced to restart after install and can’t seem to find any way to force the Startup Application manager to start an application at any time other than startup.

Answer

Well, after a lot of searching and some prompting from the comments, I found that the issue lied with how the program was initially being started.

As mentioned in the update, the first run is always started by an ssh connection. I knew there was a slight problem with this ssh connection, as it seemed to hold onto the connection no matter what I did. It turns out that this was causing the problem that resulted in the Bash instance and the Java instance remaining attached.

The solution for this problem was found here: jsch ChannelExec run a .sh script with nohup “lose” some commands

After managing to get the initial setup to start with nohup properly, the issue has gone away.

Advertisement

Answer