[Python] SIGUSR1 signal mysteriously fails with `tar`, kills process instead of reporting...

I'm executing a tar process with the subprocess module and I discovered the ability to use signals to get progress information out of it (send to stderr).

$ tar -xpf archive.tar --totals=SIGUSR1 ./blah
$ pkill -SIGUSR1 tar # separate terminal, session etc.


Unfortunately, I am unable to replicate this sequence successfully in Python.

import os
import subprocess
import signal
import time
import sys

# Define the command to execute
command = ["tar", "-xpf", sys.argv[2], "-C", sys.argv[1], "--totals=SIGUSR1"]

# Start the subprocess
print(' '.join(command))
process = subprocess.Popen(command, preexec_fn=os.setsid, stderr=subprocess.PIPE)

try:
while True:
# Ping the subprocess with SIGUSR1 signal
# NOTWORK: process.send_signal(signal.SIGUSR1)
# NOTWORK: os.killpg(os.getpgid(process.pid), signal.SIGUSR1)
subprocess.Popen(["kill", "-SIGUSR1", str(process.pid)])

print(process.stderr.readline().decode("utf-8").strip())
# print(process.stdout.readline().decode("utf-8").strip())

# Wait for a specified interval
time.sleep(1.9) # Adjust the interval as needed

except KeyboardInterrupt:
# Handle Ctrl+C to gracefully terminate the script
process.terminate()

# Wait for the subprocess to complete
process.wait()


The only style that works is opening a kill process with Popen like a cave man.

I noticed that after using os.kill or Popen.send_signal, the .poll() method returns -10. Seems like it dies after receiving the signal for some reason?

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