How to find/kill a specific python program - linux

Question

There are two different python programs running in this VM
one is a background job who monitors a folder and then 'does stuff' (with several workers)
10835 ? Sl 0:03 python main.py
10844 ? Sl 34:02 python main.py
10845 ? S 33:43 python main.py
the second one is started via script
20056 pts/1 S+ 0:00 /bin/bash ./exp.sh
20069 pts/1 S+ 0:00 /bin/bash ./exp.sh
20087 pts/1 S+ 0:10 python /home/path/second.py
i have tried numerous things to find a way to kill only the main program (i want to build a cron watchdog), but non succeded
first one i want to find only the hanging 'python main.py' process (accompanied by [defunct]), but i cant even find just this process alone.
the upper ones are from ps -ax (so they both are running currently)
pgrep 'python' returns all PIDs, also from second.py which i dont want: (not usefull, so is pkill therefore)
pgrep 'python'
10835
10844
10845
20087
pgrep 'python main.py' always returns empty, so does pgrep 'main.py;
the only thing which works
ps ax | grep 'python main.py'
but this one also returns its own PID, grepping 'ps' isn't a prefered solution afair. when main.py hangs, it shows "python main.py [defunct]". a
ps ax | grep 'python main.py [defunct]'
is useless as test as it always returns true. pgrep for anything more than 'python' also returns always false. i am a bit clueless.

Answer 1

This works for me. Found it on the pgrep bro pages.
Find the pids of processes with 'test.py' as an argument, like 'python test.py'
pgrep -f test.py
And I use it to check if a python process is running:
searcher="backend/webapi.py"
if pgrep -f "$searcher" > /dev/null
then
echo "$(date +%y-%m-%d-%H-%M-%S) $searcher is alive. Doing nothing."
else
echo "No $searcher. Kickstarting..."
pushd $HOME/there/;
./run_backend
popd;
echo "Pgrepping $searcher:"
pgrep "$searcher" # out to loggers
fi

Answer 2

In your daemon python script you should create PID file:
def writePidFile():
pid = str(os.getpid())
f = open('/tmp/my_pid', 'w')
f.write(pid)
f.close()
Now killing this process is simple:
kill `cat /tmp/my_pid`
Or you can just use grep and filter its own process:
ps ax | grep 'python main.py [defunct]' | grep -v grep

Answer 3

I think I've found a pretty safe way to do find the proper python process PID for a specific file only. The idea is to find all the python processes, then all "test.py" processes and intersect the results to find the correct PID.
I use the subprocess module in a python script (you can interpolate for .sh script):
import subprocess as subp
#Get a list of all processes with a certain name
def get_pid(name):
return list(map(int,subp.check_output(["pidof", "-c", name]).split()))
#Get a list of all pids for python3 processes
python_pids = get_pid('python3')
#Get a list of all pids for processes with "main.py" argument
main_py_pids = list(map(int,subp.check_output(["pgrep", "-f", "main.py"]).split()))
python_main_py_pid = set(python_pids).intersection(main_py_pids)
print(python_pids)
print(main_py_pids)
print(python_main_py_pid)
Result with 3 running python processes (including the one from this script) and one "sudo nano main.py" process:
Python pids: [3032, 2329, 1698]
main.py pids: [1698, 3031]
Interesection: {1698}