How do I restart a python program on my pi when it crashes?

Question

I have a python program named endless.py. I want to restart it whenever it crashes, and write the time that it restarted, to a file named restartlog.txt. Here is my python code so far:

import time, os, subprocess
while True:
        x = os.popen('ps -ef | grep python').read()
        if 'endless.py' not in x:
                print 'Restarted'
                y = open('restartlog.txt', 'a')
                y.seek(0)
                x = time.asctime( time.localtime(time.time()))
                z = '\nRestarted at', x
                z = str(z)
                y.write(z)
                print 'Written!'
                subprocess.call('python endless.py', shell=True)
        time.sleep(1)

This restarts the program, but it also creates a new one called /bin/sh -c /usr/bin/python /home/pi/endless.py. It also doesn't write to the file unless I remove the subprocess.call() (I checked). Is there any way to restart the program cleanly and write it to a file in linux or python?

score 3 · Accepted Answer · answered Mar 25 '14 at 16:43

You can do this very easily with a shell script:

#!/bin/sh

COMMAND=endless.py
LOGFILE=restart.txt

writelog() {
  now=`date`
  echo "$now $*" >> $LOGFILE
}

writelog "Starting"
while true ; do
  $COMMAND
  writelog "Exited with status $?"
  writelog "Restarting"
done

If you really want to use python:

#!/usr/bin/env python

import time, subprocess

COMMAND=['/path/to/endless.py']
LOGFILE='/path/to/restart.txt'

def writelog(message):
    with open(LOGFILE,'a') as f:
        f.write("{0} {1}\n".format(time.asctime( time.localtime(time.time())),
                                   message))

writelog("Starting")
while True:
    rc = subprocess.call(COMMAND)
    if rc >= 0:
        writelog("Exited with {0} status".format(rc))
    else:
        writelog("Exited on signal {0}".format(0-rc))
    writelog("Restarting")

score 0 · Answer 2 · answered Mar 25 '14 at 10:52

The problem is that subprocess.call waits for the command to complete.

An alternative would be to use subprocess.Popen instead, for example

import time, subprocess

# Logging function
def AddLog(status):
    # Add line to status log
    logFile = open('restartlog.txt', 'a')
    timeString = time.asctime(time.localtime(time.time()))
    logFile.write('%s %s\n' % (timeString, status))
    # Force the log to be written out
    logFile.flush()
    logFile.close()

# Start the process first time
process = subprocess.Popen(['python', 'endless.py'])
AddLog('Started')

while True:
    # Check the state of the process
    status = process.poll()

    if status != None:
        # Terminated, restart process
        process = subprocess.Popen(['python', 'endless.py'])
        print 'Termination code %d, restarted' % (status)
        AddLog('Restarted')
    else:
        # Still running
        time.sleep(1)

This has the added advantage of avoiding the ps command as well as not waiting for the command to finish.

I have to agree with Lenik though, it is really better to ensure the script does not fail, is there a problem there which you require help with?

Finally I am a little confused why you are opening the log file in append mode but immediately moving the write position to the start of the file, did you want an appending log or a single last message log?

How do I restart a python program on my pi when it crashes?

2 Answers2