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schedule a cron job to ping a server and run python script

I am trying to automate a bash script in Ubuntu. The script pings a server and then runs a python script if the packet is not received. The python script sends me a a notification when the ping is not returned. The script works when I run it manually, but it is not working when I schedule a cron job.
The bash script is named ping.sh.
#!/bin/bash
pingString=$(ping -c 1 google.com) # google is just and example, for my script I am using a server that intentionally does not return the packet.
msgRecieved="1 received, 0% packet loss"
msgLost="0 received, 100% packet loss"
if `echo ${pingString} | grep "${msgLost}" 1>/dev/null 2>&1`
then
python3 ping.py
fi
This is how I setup the cron job:
crontab -u username -e
* * * * * /bin/sh /home/username/Documents/ping.sh
I am confused because I set other dummy cron job for testing and it works fine. Example below:
* * * * * /bin/sh /home/username/Documents/test.sh
test.sh
#! /bin/bash
touch /home/username/Documents/ping_server/text.txt
The text.txt file is successfully created every minute.

Thanks for the suggestions. My problem was solved by
adding full path of the python script "ping.py" in the bash script
adding environment variables to crontab
I didn't know environment variables set in .bashrc are not loaded when running cron.
In Ubuntu it is possible to declare env variables before the jobs scheduled just like you would in bash.rc:
crontab -u username -e
ENV_VAR1=variable1
* * * * * /bin/sh /home/username/Documents/ping.sh

crontab python script query

I have a python script on a Pi3 which sends sensor readings to a mysql database, which I would like to run at boot. I have tried several combinations of #boot within crontab, but the database table never gets any fresh data.
The first line of the script is...
#!/usr/bin/python
and the script runs with:
./distance2.py
#reboot /home/pi/distance2.py &
# #reboot cd /pyhome/pi/Pimoroni/VL53L1X/Examples && sudo python distance2.py
# #reboot /home/pi/Pimoroni/VL53L1X/Examples/distance2.py &
(I moved the script from the Pimoroni directory for the sake of simplicity.)
When run from terminal, the script works perfectly:
pi#raspberrypi:~ $ ./distance2.py
distance.py
Display the distance read from the sensor.
Uses the "Short Range" timing budget by default.
Press Ctrl+C to exit.
VL53L1X Start Ranging Address 0x29
VL53L0X_GetDeviceInfo:
Device Name : VL53L1 cut1.1
Device Type : VL53L1
Device ID :
ProductRevisionMajor : 1
ProductRevisionMinor : 15
Distance: 0mm
(1L, 'record inserted.')
Distance: 60mm
(1L, 'record inserted.')
Distance: 60mm
grep shows it's running OK (Unless the red colour of the script name text means something bad?)
ps aux | grep distance2.py
pi 1530 0.0 0.5 7332 2032 pts/0 S+ 16:20 0:00 grep --color=auto distance2.py
What's crontab #boot got against my humble project?

Try full path to the python and write the log for investigation:
#reboot /usr/bin/python /home/pi/distance2.py > /home/pi/distance2_cronjoblog 2>&1

Python script not working when launched at startup of RPi

RPi 1B with V1 cam.
Python script takes a picture when pushbutton hooked to gpio is pressed. Then picture is emailed via Mutt.
All working fine when doing step by step.
But not doing as intended when lauched automatically at startup.
import subprocess
from datetime import datetime
from gpiozero import Button
button = Button(17)
while True:
button.wait_for_press()
time = datetime.now()
filename = "capture-%04d%02d%02d-%02d%02d%02d.jpg" % (time.year, time.month, time.day, time.hour, time.minute, time.second)
subprocess.call("raspistill -t 500 -o %s" % filename, shell=True)
subprocess.call("echo "" | mutt -s 'Someone at the door' -i messageBody.txt myname#mailprovider.com -a %s" % filename, shell=True)
All working fine when typing :
$ python raspicam.py
I get a nice email within seconds with picture attached to it.
Next logical step is to get this script to be launched at startup:
$ nano launcher.sh
#!/bin/sh
# launcher.sh
cd /
cd home/pi
python doorbell02.py
cd /
$ chmod 755 launcher.sh
$ sh launcher.sh
Then get it to be launched at startup via cron :
$ mkdir logs
$ sudo crontab -e
add: #reboot sh /home/pi/launcher.sh >/home/pi/logs/cronlog 2>&1
At next reboot all working fine except sending mail via with mutt.
$ ps aux shows that my python script and script launcher belongs to "root"... is it where trouble comes from ?
root 475 0.0 0.0 0 0 ? S 16:51 0:00 [cifsd]
root 500 0.0 0.6 7932 2300 ? Ss 16:51 0:00 /usr/sbin/cron -f
root 502 0.0 0.6 9452 2384 ? S 16:51 0:00 /usr/sbin/CRON -f
root 506 0.0 0.3 1924 1148 ? Ss 16:51 0:00 /bin/sh -c sh /home/pi/launcher.sh >/home/pi/logs/cronlog 2>&1
root 511 0.0 0.2 1924 1108 ? S 16:51 0:00 sh /home/pi/launcher.sh
root 513 1.5 2.5 34348 9728 ? Sl 16:51 4:25 python doorbell02.py
I am also unable to get pdb to work alongside with my script to get some log or debug info...
Some hints would be very appreciated
Thank you very much for your time

Try using absolute paths in your code.
It helped me in my case.

Starting ngrok and python app on startup

I am currently running ngrock and a python app concurrently on a specific port to text my raspberry pi, and have it respond accordingly to my message via Twilio. Each time my raspberry pi boots up, or reboots, I need to manually start the services again with ./ngrok http 5000 and python /path/to/file/app.py. To avoid that, I edited my cron jobs as follows, and wrote a script called startService.py. However, it doesn't seem to be functioning properly, as I do not receive answers to texts after reboot. Any ideas?
Cron:
# m h dom mon dow command
*/5 * * * * python /rasp/system/systemCheck.py
#reboot python /Rasp/system/twilio/startService.py &
startService.py
import os
os.system('/./ngrok http -subdomain=ABC123 5000')
os.system('python /Rasp/system/twilio/starter/app.py')

You did not mention your OS, assuming your OS using Upstart for boot you can create upstart script to start then your process will automatically spawn at boot or when the process die. For ngrok, create a file /etc/init/ngrok.conf
# Ngrok
#
# Create tunnel provided by ngrok.io
description "Ngrok Tunnel"
start on runlevel [2345]
stop on runlevel [!2345]
respawn
respawn limit 10 5
umask 022
exec /ngrok http -subdomain={{My Reserved Subdomain}} 5000
Now it will automaticlaly start at boot. If you want to start manually just issue command.
$ sudo service ngrok start
Just for suggestion, putting your binary on root directory / is not good practice.
Reference:
http://notes.rioastamal.net/2016/05/starting-ngrok-automatically-at-boot.html

After multiple failed attempts I have seem to come up with a working system. I first had to authorize the root user to use my ngrok account by doing the following:
sudo su
./ngrok authtoken {{Insert Your Auth Token Here}}
exit
Then, I created ngrokLauncher.sh and appLauncher.sh as shown.
ngrokLauncher.sh:
#!/bin/sh
# launcher.sh
cd /
./ngrok http -subdomain={{My Reserved Subdomain}} 5000 &
cd /
appLauncher.sh:
#!/bin/sh
# launcher.sh
cd /Storage/system/twilio/starter
python app.py &
cd /
Then, I modified the file permissions so they would be able to be run on startup sudo chmod 755 ngrokLauncher.sh && sudo chmod 755 appLauncher.sh. Lastly, I edited the Cron Jobs as follows:
Crontab:
# m h dom mon dow command
*/5 * * * * python /SKYNET/system/systemCheck.py
#reboot sh /Storage/ngrokLauncher.sh >/Storage/logs/cronlog 2>&1
#reboot sh /Storage/appLauncher.sh >/Storage/logs/cronlog 2>&1
Then after running sudo reboot, the system restarted and I received a response to my sms from the python app.

Crontab not restarting process

I am trying to setup a crontab to run 6 python data scrapers. I am tired of having to restart them manually when one of them fails. When running the following:
> ps -ef | grep python
ubuntu 31537 1 0 13:09 ? 00:00:03 python /home/ubuntu/scrapers/datascraper1.py
etc... I get a list of the datascrapers 1-6 all in the same folder.
I edited my crontab like this:
sudo crontab -e
# m h dom mon dow command
* * * * * pgrep -f /home/ubuntu/scrapers/datascraper1.py || python /home/ubuntu/scrapers/datascraper1.py > test.out
Then I hit control+X to exit and hit yes to save as /tmp/crontab.M6sSxL/crontab .
However it does not work in restarting or even starting datascraper1.py whether I kill the process manually or if the process fails on its own. Next, I tried reloading cron but it still didn't work:
sudo cron reload
Finally I tried removing nohup from the cron statement and that also did not work.
How can I check if a cron.allow or cron.deny file exists?
Also, do I need to add a username before pgrep? I am also not sure what the "> test.out" is doing at the end of the cron statement.
After running
grep CRON /var/log/syslog
to check to see if cron ran at all, I get this output:
ubuntu#ip-172-31-29-12:~$ grep CRON /var/log/syslog
Jan 5 07:01:01 ip-172-31-29-12 CRON[31101]: (root) CMD (pgrep -f datascraper1.py ||
python /home/ubuntu/scrapers/datascraper1.py > test.out)
Jan 5 07:01:01 ip-172-31-29-12 CRON[31100]: (CRON) info (No MTA installed, discarding output)
Jan 5 07:17:01 ip-172-31-29-12 CRON[31115]: (root) CMD ( cd / && run-parts --report /etc/cron.hourly)
Jan 5 08:01:01 ip-172-31-29-12 CRON[31140]: (root) CMD (pgrep -f datascraper1.py || python /home/ubuntu/scrapers/datascraper1.py > test.out)
Since there is evidence of Cron executing the command, there must be something wrong with this command, (note: I added the path to python):
pgrep -f datascraper1.py || /usr/bin/python /home/ubuntu/scrapers/datascraper1.py > test.out
Which is supposed to check to see if datascaper1.py is running, if not then restart it.
Since Cron is literally executing this statement:
(root) CMD (pgrep -f datascraper1.py || python /home/ubuntu/scrapers/datascraper1.py > test.out)
aka
root pgrep -f datascraper1.py
Running the above root command gives me:
The program 'root' is currently not installed. You can install it by typing:
sudo apt-get install root-system-bin
Is there a problem with Cron running commands from root?
Thanks for your help.

First of all, you need to see if cron is working at all.
Add this to your cron file (and ideally delete the python statement for now, to have a clear state)
* * * * * echo `date` >>/home/your_username/hello_cron
This will output the date in the file "hello_cron" every minute. Try this, and if this works, ie you see output every minute, write here and we can troubleshoot further.
You can also look in your system logs to see if cron has ran your command, like so:
grep CRON /var/log/syslog
Btw the >test.out part would redirect the output of the python program to the file test.out. I am not sure why you need the nohup part - this would let the python programs run even if you are logged out - is this what you want?
EDIT: After troubleshooting cron:
The message about no MTA installed means that cron is trying to send you an e-mail with the output of the job but cannot because you dont have an email programm installed:
Maybe this will fix it:
sudo apt-get install postfix
The line invoking the python program in cron is producing some output (an error) so it's in your best interests to see what happens. Look at this tutorial to see how to set your email address: http://www.cyberciti.biz/faq/linux-unix-crontab-change-mailto-settings/
Just in case the tutorial becomes unavailable:
MAILTO:youremail#example.com

You need to add python home to your path at the start of the job, however you have python set up. When you're running it yourself and you type python, it checks where you are, then one level down, then your $PATH. So, python home (where the python binary is) needs to be globally exported for the user that owns the cron (so, put it in a rc script in /etc/rc.d/) or, you need to append the python home to path at the start of the cron job. So,
export PATH=$PATH:<path to python>
Or, write the cron entry as
/usr/bin/python /home/ubuntu/etc/etc
to call it directly. It might not be /usr/bin, run the command
'which python'
to find out.
The 'No MTA' message means you are getting STDERR, which would normally get mailed to the user, but can't because you have no Mail Transfer Agent set up, like mailx, or mutt, so no mail for the user can get delivered from cron, so it is discarded. If you'd like STDERR to go into the log also, at the end, instead of
"command" > test.out
write
"command" 2>&1 > test.out
to redirect STDERR into STDOUT, then redirect both to test.out.