How to check if a specific executable has a live process - bash

Question

I want to write a script that checks periodically if a specific executable has a live process, something like this:
psping [-c ###] [-t ###] [-u user-name] exe-name
-c - limit amount of pings, Default is infinite
-t - define alternative timeout in seconds, Default is 1 sec
-u - define user to check process for. The default is ANY user.
For example, psping java will list all processes that are currently invoked by the java command.
The main goal is to count and echo the number of live processes for a user, whose executable file is exe-name, java in the above example.
I wrote a function:
perform_ping(){
ps aux | grep "${EXE_NAME}" | awk '{print $2}' | while read PID
do
echo $PID # -> This will echo the correct PID
# How to find if this PID was executed by ${EXE_NAME}
done
fi
sleep 1
}
I'm having a hard time figuring out how to check if a specific executable file has a live process.

Answer 1

To list all processes that opens a file, we can use the lsof command. Because an executable must be opened in order to be run, we may just use lsof for this purpose.
The next problem is that when we run a java file, we simply type java some_file, and if we issue lsof java it will coldly says that lsof: status error on java: No such file or directory because the java is actually /usr/bin/java.
To convert from java to /usr/bin/java we can use which java, so the command would be:
lsof $(which $EXE_FILE)
The output may looks like this:
lsof: WARNING: can't stat() tracefs file system /sys/kernel/debug/tracing
Output information may be incomplete.
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
python3 26969 user txt REG 8,1 4526456 15409 /usr/bin/python3.6
In this case I searched python3 as lsof $(which python3). It will report the PID in the second field. But when there's another user that invokes python3 too, lsof will issue the warning on stderr like the first two lines because it cannot read other users info. Therefore, we modify the command as:
lsof $(which python3) 2> /dev/null
to suppress the warning. Then we're almost there:
lsof $(which python3) 2> /dev/null | awk 'NR > 1 { print $2 }'
Then you can use read to catch the PID.
Edit: how to list all processes for all users?
By default lsof doesn't read process for a specific file, but after further reading man lsof I found that there are options that meet your needs.
-a causes list selection options to be ANDed.
-c c selects the listing of files for processes executing the command that begins with the characters of c. Multiple commands may be specified, using multiple -c options.
-u s selects the listing of files for the user whose login names or user ID numbers are in the comma-separated set s.
Therefore, you can use
lsof -c java
to list all commands that are run by java. And to see a specific user, add -u option as
lsof -a -c java -u user
-a is needed for the AND operation. If you run this command you will see multiple entry for a process, to unique them, run
lsof -c java 2> /dev/null | sed 1d | sort -uk2,2
Also please notice that users may run their own java in their path and therefore you have to decide which one to monitor: java or /usr/bin/java.