Check to see if python script is running

Question

I have a python daemon running as a part of my web app  How can I quickly check  using python  if my daemon is running and  if not  launch it   I want to do it that way to fix any crashes of the daemon  and so the script does not have to be run manually  it will automatically run as soon as it is called and then stay running   How can i check  using python  if my script is running

User · Answer

try this      usr bin env python import os  sys  atexit  try        Set PID file     def set pid file            pid   str os getpid            f   open  myCode pid    w           f write pid          f close        def goodby            pid   str  myCode pid           os remove pid       atexit register goodby      set pid file         Place your code here  except KeyboardInterrupt      sys exit 0

User · Answer

Try this other version  def checkPidRunning pid                  Check For the existence of a unix pid              try          os kill pid  0      except OSError          return False     else          return True    Entry point if   name         main         pid   str os getpid        pidfile   os path join       tmp     program     pid        if os path isfile pidfile  and checkPidRunning int file pidfile  r   readlines   0                 print   s already exists  exiting    pidfile             sys exit       else          file pidfile   w   write pid         Do some actual work here     main        os unlink pidfile

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There are a myriad of options  One method is using system calls or python libraries that perform such calls for you  The other is simply to spawn out a process like   ps ax   grep processName   and parse the output  Many people choose this approach  it isn t necessarily a bad approach in my view

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Of course the example from Dan will not work as it should be   Indeed  if the script crash  rise an exception  or does not clean pid file  the script will be run multiple times   I suggest the following based from another website    This is to check if there is already a lock file existing     usr bin env python import os import sys if os access os path expanduser     lockfile vestibular lock    os F OK            if the lockfile is already there then check the PID number          in the lock file         pidfile   open os path expanduser     lockfile vestibular lock     r           pidfile seek 0          old pid   pidfile readline             Now we check the PID from lock file matches to the current           process PID         if os path exists   proc  s    old pid                   print  You already have an instance of the program running                  print  It is running as process  s     old pid                 sys exit 1          else                  print  File is there but the program is not running                  print  Removing lock file for the   s as it can be there because of the program last time it was run    old pid                 os remove os path expanduser     lockfile vestibular lock      This is part of code where we put a PID file in the lock file  pidfile   open os path expanduser     lockfile vestibular lock     w   pidfile write   s    os getpid    pidfile close     This code will check the value of pid compared to existing running process   avoiding double execution   I hope it will help

User · Answer

There are very good packages for restarting processes on UNIX   One that has a great tutorial about building and configuring it is monit    With some tweaking you can have a rock solid proven technology keeping up your daemon

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Here is more useful code  with checking if exactly python executes the script        usr bin env python  import os from sys import exit   def checkPidRunning pid       global script name     if pid lt 1          print  Incorrect pid number           exit       try          os kill pid  0      except OSError          print  Abnormal termination of previous process           return False     else          ps command    ps -o command   s   grep -Eq  python     s      pid script name          process exist   os system ps command          if process exist    0              return True         else              print  Process with pid  s is not a Python process  Continue       pid             return False   if   name         main         script name   os path basename   file        pid   str os getpid        pidfile   os path join       tmp    script name   pid       if os path isfile pidfile           print  Warning  Pid file  s existing  Checking for process       pidfile         r pid   int file pidfile  r   readlines   0           if checkPidRunning r pid               print  Python process with pid    s is already running  Exit     r pid             exit           else              file pidfile   w   write pid      else          file pidfile   w   write pid     main programm            os unlink pidfile    Here is string   ps command    ps -o command   s   grep -Eq  python     s      pid script name    returns 0 if  grep   is successful  and the process  python  is currently running with the name of your script as a parameter

User · Answer

I m a big fan of Supervisor for managing daemons   It s written in Python  so there are plenty of examples of how to interact with or extend it from Python   For your purposes the XML-RPC process control API should work nicely

User · Answer

Consider the following example to solve your problem      usr bin python   - - coding  latin-1 - -  import os  sys  time  signal  def termination handler  signum frame       global running     global pidfile     print  You have requested to terminate the application         sys stdout flush       running   0     os unlink pidfile   running   1 signal signal signal SIGINT termination handler   pid   str os getpid    pidfile     tmp   os path basename   file    split      0    pid   if os path isfile pidfile       print   s already exists  exiting    pidfile     sys exit   else      file pidfile   w   write pid     Do some actual work here  while running    time sleep 10    I suggest this script because it can be executed one time only

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ps ax   grep processName   if yor debug script in pycharm always exit  pydevd py --multiproc --client 127 0 0 1 --port 33882 --file processName

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My solution is to check for the process and command line arguments Tested on windows and ubuntu linux  import psutil import os  def is running script       for q in psutil process iter            if q name   startswith  python                if len q cmdline    gt 1 and script in q cmdline   1  and q pid   os getpid                    print       Process is already running  format script                   return True      return False   if not is running  test py        n   input  What is Your Name         print   Hello     n

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The pid library can do exactly this   from pid import PidFile  with PidFile      do something     It will also automatically handle the case where the pidfile exists but the process is not running

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A simple example if you only are looking for a process name exist or not   import os  def pname exists inp       os system  ps -ef  gt   tmp psef       lines open   tmp psef    r   read   split   n       res  i for i in lines if inp in i      return True if res else False  Result  In  21   pname exists  syslog   Out 21   True  In  22   pname exists  syslog    Out 22   False

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Drop a pidfile somewhere  e g   tmp   Then you can check to see if the process is running by checking to see if the PID in the file exists  Don t forget to delete the file when you shut down cleanly  and check for it when you start up     usr bin env python  import os import sys  pid   str os getpid    pidfile     tmp mydaemon pid   if os path isfile pidfile       print   s already exists  exiting    pidfile     sys exit   file pidfile   w   write pid  try        Do some actual work here finally      os unlink pidfile    Then you can check to see if the process is running by checking to see if the contents of  tmp mydaemon pid are an existing process  Monit  mentioned above  can do this for you  or you can write a simple shell script to check it for you using the return code from ps   ps up  cat  tmp mydaemon pid    gt  dev null  amp  amp  echo  Running     echo  Not running    For extra credit  you can use the atexit module to ensure that your program cleans up its pidfile under any circumstances  when killed  exceptions raised  etc

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Came across this old question looking for solution myself   Use psutil   import psutil import sys from subprocess import Popen  for process in psutil process iter        if process cmdline        python    your script py            sys exit  Process found  exiting     print  Process not found  starting it    Popen   python    your script py

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Using bash to look for a process with the current script s name  No extra file   import commands import os import time import sys  def stop if already running        script name   os path basename   file        l   commands getstatusoutput  ps aux   grep -e   s    grep -v grep   awk   print  2    awk   print  2      script name      if l 1           sys exit 0     To test  add  stop if already running   print  running normally  while True      time sleep 3

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This is what I use in Linux to avoid starting a script if already running   import os import sys   script name   os path basename   file    pidfile   os path join   tmp   os path splitext script name  0       pid    def create pidfile        if os path exists pidfile           with open pidfile   r   as  file              last pid   int  file read               Checking if process is still running         last process cmdline     proc  d cmdline    last pid         if os path exists last process cmdline               with open last process cmdline   r   as  file                  cmdline    file read               if script name in cmdline                  raise Exception  Script already running           with open pidfile   w   as  file          pid   str os getpid             file write pid    def main           Your application logic goes here      if   name         main         create pidfile       main     This approach works good without any dependency on an external module

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The other answers are great for things like cron jobs  but if you re running a daemon you should monitor it with something like daemontools

User · Answer

A technique that is handy on a Linux system is using domain sockets  import socket import sys import time  def get lock process name         Without holding a reference to our socket somewhere it gets garbage       collected when the function exits     get lock  lock socket   socket socket socket AF UNIX  socket SOCK DGRAM       try            The null byte   0  means the socket is created            in the abstract namespace instead of being created            on the file system itself            Works only in Linux         get lock  lock socket bind   0    process name          print  I got the lock      except socket error          print  lock exists          sys exit     get lock  running test   while True      time sleep 3   It is atomic and avoids the problem of having lock files lying around if your process gets sent a SIGKILL You can read in the documentation for socket close that sockets are automatically closed when garbage collected

User · Answer

Rather than developing your own PID file solution  which has more subtleties and corner cases than you might think   have a look at supervisord -- this is a process control system that makes it easy to wrap job control and daemon behaviors around an existing Python script

[python] Check to see if python script is running

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