How to control background process in linux

Question

I need to write a script in Linux which can start a background process using one command and stop the process using another.

The specific application is to take userspace and kernel logs for android.

following command should start taking logs

$ mylogscript start

following command should stop the logging

$ mylogscript stop

Also, the commands should not block the terminal. For example, once I send the start command, the script run in background and I should be able to do other work on terminal.

Any pointers on how to implement this in perl or python would be helpful.

EDIT: Solved: https://stackoverflow.com/a/14596380/443889

Answer 1

I got the solution to my problem. Solution essentially includes starting a subprocess in python and sending a signal to kill the process when done. Here is the code for reference:

#!/usr/bin/python

import subprocess
import sys
import os
import signal

U_LOG_FILE_PATH = "u.log"
K_LOG_FILE_PATH = "k.log"
U_COMMAND = "adb logcat > " + U_LOG_FILE_PATH
K_COMMAND = "adb shell cat /proc/kmsg > " + K_LOG_FILE_PATH

LOG_PID_PATH="log-pid"

def start_log():
    if(os.path.isfile(LOG_PID_PATH) == True):
        print "log process already started, found file: ", LOG_PID_PATH
        return
    file = open(LOG_PID_PATH, "w")
    print "starting log process: ", U_COMMAND
    proc = subprocess.Popen(U_COMMAND,
        stdout=subprocess.PIPE, stderr=subprocess.PIPE,
        shell=True, preexec_fn=os.setsid)
    print "log process1 id = ", proc.pid
    file.write(str(proc.pid) + "\n")
    print "starting log process: ", K_COMMAND
    proc = subprocess.Popen(K_COMMAND,
        stdout=subprocess.PIPE, stderr=subprocess.PIPE,
        shell=True, preexec_fn=os.setsid)
    print "log process2 id = ", proc.pid
    file.write(str(proc.pid) + "\n")
    file.close()

def stop_log():
    if(os.path.isfile(LOG_PID_PATH) != True):
        print "log process not started, can not find file: ", LOG_PID_PATH
        return
    print "terminating log processes"
    file = open(LOG_PID_PATH, "r")
    log_pid1 = int(file.readline())
    log_pid2 = int(file.readline())
    file.close()
    print "log-pid1 = ", log_pid1
    print "log-pid2 = ", log_pid2
    os.killpg(log_pid1, signal.SIGTERM)
    print "logprocess1 killed"
    os.killpg(log_pid2, signal.SIGTERM)
    print "logprocess2 killed"
    subprocess.call("rm " + LOG_PID_PATH, shell=True)

def print_usage(str):
    print "usage: ", str, "[start|stop]"

# Main script
if(len(sys.argv) != 2):
    print_usage(sys.argv[0])
    sys.exit(1)

if(sys.argv[1] == "start"):
    start_log()
elif(sys.argv[1] == "stop"):
    stop_log()
else:
    print_usage(sys.argv[0])
    sys.exit(1)

sys.exit(0)