Daemonizing a python script in debian

Question

I have a python script that i want to run in the background on startup. This is the script:

#!/usr/bin/python
from Adafruit_CharLCD import Adafruit_CharLCD
from subprocess import * 
from time import sleep, strftime
from datetime import datetime
from datetime import timedelta
from os import system
from os import getloadavg
from glob import glob

#Variables
lcd = Adafruit_CharLCD() #Stores LCD object
cmdIP = "ip addr show eth0 | grep inet | awk '{print $2}' | cut -d/ -f1" #Current IP
cmdHD = "df -h / | awk '{print $5}'" # Available hd space
cmdSD = "df -h /dev/sda1 | awk '{print $5}'" # Available sd space
cmdRam = "free -h"
temp = 0

#Run shell command
def run_cmd(cmd):
    p = Popen(cmd, shell=True, stdout=PIPE)
    output = p.communicate()[0]
    return output

#Initalises temp device     
def initialise_temp():
    #Initialise
    system("sudo modprobe w1-gpio")
    system("sudo modprobe w1-therm")
    #Find device
    devicedir = glob("/sys/bus/w1/devices/28-*")
    device = devicedir[0]+"/w1_slave"
    return device

#Gets temp  
def get_temp(device):
    f = open (device, 'r')
    sensor = f.readlines()
    f.close()

    #parse results from the file
    crc=sensor[0].split()[-1]
    temp=float(sensor[1].split()[-1].strip('t='))
    temp_C=(temp/1000.000)
    temp_F = ( temp_C * 9.0 / 5.0 ) + 32

    #output
    return temp_C

#Gets time
def get_time():
    return datetime.now().strftime('%b %d  %H:%M:%S\n')

#Gets uptime
def get_uptime():
    with open('/proc/uptime', 'r') as f:
        seconds = float(f.readline().split()[0])
        array = str(timedelta(seconds = seconds)).split('.')
        string = array[0].split(' ')
        totalString = string[0] + ":" + string[2]
    return totalString

#Gets average load
def get_load():
    array = getloadavg()
    average = 0
    for i in array:
        average += i
    average = average / 3
    average = average * 100
    average = "%.2f" % average
    return str(average + "%")

#def get_ram():
def get_ram():
    ram = run_cmd(cmdRam)
    strippedRam = ram.replace("\n"," ");
    splitRam = strippedRam.split(' ')
    totalRam = int(splitRam[52].rstrip("M"))
    usedRam = int(splitRam[59].rstrip("M"))
    percentage = "%.2f" % ((float(usedRam) / float(totalRam)) * 100)
    return percentage + "%"

#Gets the SD usage
def get_sd():
    sd = run_cmd(cmdSD)
    strippedSD = sd.lstrip("Use%\n")
    return strippedSD

#Gets the HD usage
def get_hd():
    hd = run_cmd(cmdSD)
    strippedHD = hd.lstrip("Use%\n")
    return strippedHD

def scroll():
    while(1):
        lcd.scrollDisplayLeft()
        sleep(0.5)

#Uptime and IP
def screen1():
    uptime = get_uptime()
    lcd.message('Uptime %s\n' % (uptime))
    ipaddr = run_cmd(cmdIP)
    lcd.message('IP %s' % (ipaddr))

#Ram and load
def screen2():
    ram = get_ram()
    lcd.message('Ram Used %s\n' % (ram))
    load = get_load()
    lcd.message('Avg Load %s' % (load))

#Temp and time
def screen3():
    time = get_time();
    lcd.message('%s\n' % (time))
    lcd.message('Temp %s' % (temp))

#HD and SD usage
def screen4():
    sd = get_sd()
    lcd.message('SD Used %s\n' % (sd))
    hd = get_hd()
    lcd.message('HD Used %s' % (hd))

#Pause and clear
def screenPause(time):
    sleep(time)
    #In here to reduce lag
    global temp
    temp = str(get_temp(device));
    lcd.clear()
###########################################################################################################

#Initialise
lcd.begin(16,2)
device = initialise_temp()
lcd.clear()

#Testing

#Main loop
while(1):
    screen1()
    screenPause(5)
    screen2()
    screenPause(5)
    screen3()
    screenPause(5)
    screen4()
    screenPause(5)

I know i probably havnt done things the write way but its the first attempt. My startup script is in /etc/init.d This is the script:

#! /bin/sh
### BEGIN INIT INFO
# Provides:          LCD looping
# Required-Start:    $remote_fs $syslog
# Required-Stop:     $remote_fs $syslog
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: LCD daemon
# Description:       This file should be used to construct scripts to be
#                    placed in /etc/init.d.
### END INIT INFO

# Author: Foo Bar <foobar@baz.org>
#
# Please remove the "Author" lines above and replace them
# with your own name if you copy and modify this script.

# Do NOT "set -e"

# PATH should only include /usr/* if it runs after the mountnfs.sh script
PATH=/sbin:/usr/sbin:/bin:/usr/bin
DESC="Loops the LCD screen through LCD.py"
NAME=startup.py
DAEMON=/home/pi/Programming/LCD/startup.py
DAEMON_ARGS=""
PIDFILE=/var/run/daemonLCD.pid
SCRIPTNAME=/etc/init.d/daemonLCD

# Exit if the package is not installed
[ -x "$DAEMON" ] || exit 0

# Read configuration variable file if it is present
[ -r /etc/default/daemonLCD ] && . /etc/default/daemonLCD

# Load the VERBOSE setting and other rcS variables
. /lib/init/vars.sh

# Define LSB log_* functions.
# Depend on lsb-base (>= 3.2-14) to ensure that this file is present
# and status_of_proc is working.
. /lib/lsb/init-functions

#
# Function that starts the daemon/service
#
do_start()
{
        # Return
        #   0 if daemon has been started
        #   1 if daemon was already running
        #   2 if daemon could not be started
        start-stop-daemon --start --quiet --pidfile $PIDFILE --exec $DAEMON --test > /dev/null \
                || return 1
        start-stop-daemon --start --quiet --pidfile $PIDFILE --exec $DAEMON -- \
                $DAEMON_ARGS \
                || return 2
        # Add code here, if necessary, that waits for the process to be ready
        # to handle requests from services started subsequently which depend
        # on this one.  As a last resort, sleep for some time.
}

#
# Function that stops the daemon/service
#
do_stop()
{
        # Return
        #   0 if daemon has been stopped
        #   1 if daemon was already stopped
        #   2 if daemon could not be stopped
        #   other if a failure occurred
        start-stop-daemon --stop --quiet --retry=TERM/30/KILL/5 --pidfile $PIDFILE --name $NAME
        RETVAL="$?"
        [ "$RETVAL" = 2 ] && return 2
        # Wait for children to finish too if this is a daemon that forks
        # and if the daemon is only ever run from this initscript.
        # If the above conditions are not satisfied then add some other code
        # that waits for the process to drop all resources that could be
        # needed by services started subsequently.  A last resort is to
        # sleep for some time.
        start-stop-daemon --stop --quiet --oknodo --retry=0/30/KILL/5 --exec $DAEMON
        [ "$?" = 2 ] && return 2
        # Many daemons don't delete their pidfiles when they exit.
        rm -f $PIDFILE
        return "$RETVAL"
#
# Function that sends a SIGHUP to the daemon/service
#
do_reload() {
        #
        # If the daemon can reload its configuration without
        # restarting (for example, when it is sent a SIGHUP),
        # then implement that here.
        #
        start-stop-daemon --stop --signal 1 --quiet --pidfile $PIDFILE --name $NAME
        return 0
}

case "$1" in
  start)
        [ "$VERBOSE" != no ] && log_daemon_msg "Starting $DESC" "$NAME"
        do_start
        case "$?" in
                0|1) [ "$VERBOSE" != no ] && log_end_msg 0 ;;
                2) [ "$VERBOSE" != no ] && log_end_msg 1 ;;
        esac
        ;;
  stop)
        [ "$VERBOSE" != no ] && log_daemon_msg "Stopping $DESC" "$NAME"
        do_stop
        case "$?" in
                0|1) [ "$VERBOSE" != no ] && log_end_msg 0 ;;
                2) [ "$VERBOSE" != no ] && log_end_msg 1 ;;
        esac
        ;;
  status)
        status_of_proc "$DAEMON" "$NAME" && exit 0 || exit $?
        ;;
  #reload|force-reload)
        #
        # If do_reload() is not implemented then leave this commented out
        # and leave 'force-reload' as an alias for 'restart'.
        #
        #log_daemon_msg "Reloading $DESC" "$NAME"
        #do_reload
        #log_end_msg $?
        #;;

  restart|force-reload)
        #
        # If the "reload" option is implemented then remove the
        # 'force-reload' alias
        #
        log_daemon_msg "Restarting $DESC" "$NAME"
        do_stop
        case "$?" in
          0|1)
                do_start
                case "$?" in
                        0) log_end_msg 0 ;;
                        1) log_end_msg 1 ;; # Old process is still running
                        *) log_end_msg 1 ;; # Failed to start
                esac
                ;;
          *)
                # Failed to stop
                log_end_msg 1
                ;;
        esac
        ;;
  *)
        #echo "Usage: $SCRIPTNAME {start|stop|restart|reload|force-reload}" >&2
        echo "Usage: $SCRIPTNAME {start|stop|status|restart|force-reload}" >&2
        exit 3
        ;;
esac

:

Im think i have missed something as when i type daemonLCD start it says command not found. Any input would be great.

Thanks

Answer 1

Assuming you may want to manage more than one daemon in the future, let me recommend Supervisord. It's much simpler than writing and managing your own init.d scripts.

For example, starting your script would be as easy as including this in the conf:

[program:myscript]
command=/usr/bin/python /path/to/myscript.py

I use an init.d script available here. Rename it to supervisord and copy it to your /etc/init.d/ then run:

sudo update-rc.d supervisord defaults

I believe that init script has supervisord run as root as default. You can have it drop to run as another user if you like. I'm not if children run as root or not, although I'd assume not. Go ahead and check, but if they don't you can stick a sudo before the python command in your supervisord.conf where you call the script.

It that doesn't run, (or if you want supervisord to run as a non-root but still want your script run as root) you can allow for anyone (or a group of users) to run the python script as root (although you should make quite certain that this script cannot be edited by anyone other than root).

edit your sudoers file with "sudo visudo" and add the following to the end:

USERS ALL=(ALL) NOPASSWD: /path/to/myscript.py

Then make sure you have a shebang at the beginning of your python script and change the command to omit the python call, i.e:

[program:myscript]
command=sudo /path/to/myscript.py

Answer 2

Here's a good blog post which deals with this question: Getting a Python script to run in the background (as a service) on boot

Answer 3

Use daemontools from djb. It is a lot easier than the other answers provided. For starters you can install daemon tools with apt-get so you do not need to worry about grabbing an unknown script from a gist and you get updates through debian like normal. daemontools also takes care of restarting the service if it dies and provides for logging. There is a description of daemontools and debian here:

http://blog.rtwilson.com/how-to-set-up-a-simple-service-to-run-in-the-background-on-a-linux-machine-using-daemontools/

djb's page aout daemontools:

http://cr.yp.to/daemontools.html

Answer 4

This is a classic mistake new Unix/Linux users make. /etc/init.d isn't in your path which is why you can't just run daemonLCD. Try using the full path (/etc/init.d/daemonLCD start) or prepending ./ (./daemonLCD start).

The script needs to be executable for either of the above to work.

Answer 5

thanks for the code above. I've been using it to figure out how to set up a daemon on a linux machine.

With some tweaking I could get it to work quite well.

But something puzzled me. And that was checking if the process was running, by checking the exists of the /var/run/myfile.pid

That's just the pidfile - NOT the process, right?

Take a look at /lib/lsb/init-functions.status_of_proc

status_of_proc () {
local pidfile daemon name status OPTIND

pidfile=
OPTIND=1
while getopts p: opt ; do
    case "$opt" in
        p)  pidfile="$OPTARG";;
    esac
done
shift $(($OPTIND - 1))

if [ -n "$pidfile" ]; then
    pidfile="-p $pidfile"
fi
daemon="$1"
name="$2"

status="0"
pidofproc $pidfile $daemon >/dev/null || status="$?"
if [ "$status" = 0 ]; then
    log_success_msg "$name is running"
    return 0
elif [ "$status" = 4 ]; then
    log_failure_msg "could not access PID file for $name"
    return $status
else
    log_failure_msg "$name is not running"
    return $status
fi
}

That's only dealing with the success or failure of accessing the PID file.

Now, I'm building this daemon to go on a small device. I've discovered it's using BusyBox and I don't have init-functions :-( But I do have pidof.

So I added

        log_success_msg "pidof $NAME is $(pidof -x $NAME)" >> $LOGFILE
       log_success_msg "PIDFILE of $NAME is" >> $LOGFILE
       sed -n '1p' < $PIDFILE >> $LOGFILE

and checked $LOGFILE and lo and behold the numbers are different.

I did pstree -s -p on both numbers and

the pidof number spits out a very short tree, so it's for the root level process

but the $PIDFILE number vomits out branch after branch, so I don't think pstree can find the process.

Yes, the do_stop in Joseph Baldwin Roberts's code will kill both processes. But if the process is killed in another way e.g. kill -9 12345, the $PIDFILE is still there. So, the daemon will falsely believe the process is already running an refuse to start.