Run a sudo (or startup) python script from cron on a Raspberry Pi?

sudo cron python startup raspberry-pi

8,880

Drop the sudo its not needed since its running as root, and sudo by default wont run without a tty.

You can tell sudo to run without a tty by running visudo and commenting out requiretty:

#Default requiretty

NOTE this does have security disadvantages see here

8,880

Author by

nivek

Updated on September 18, 2022

Comments

nivek over 1 year
I'm helping out with an art project (http://stargateeggbeater.com/ for those interested) built on Raspberry Pi. The RPi controls an addressable LED strip through the GPIO, using the spidev device per these instructions. To start the display, we run:
```
sudo python lightpaint-FF.py
```
We plan to take this project to parties and festivals, so ideally we'd like to have it start running automatically on boot. (Our RPi doesn't have a monitor connected, so right now we have to log in with another laptop using SSH and run the code using nohup before logging out again).

My first attempt at solving this problem was to write a simple bash script:
```
#!/bin/bash

if [ ! "$(pidof python)" ] 
 then
   sudo python /home/pi/lightpaint-FF.py
fi
```
And to modify /etc/crontab to include
```
* * * * * root /home/pi/EggbeaterCronJob
```
The desired behavior is to check every minute to see if any Python instances are running and, if not, start the python script. I have verified that this script works when called from a terminal:
```
pidof python # returns nothing
sudo /home/pi/EggbeaterCronJob
pidof python # returns new process ID
```
But after updating my crontab, no python process ID ever appears on its own accord. Just to be sure, I also made sure I wasn't making a boneheaded mistake in my crontab configuration:
```
* * * * * root touch test-freaking-cron
```
This verified that cron was indeed responding to my edits.
- jasonwryan almost 11 years
  
  What distro are you running on your Pi?
- goldilocks almost 11 years
  
  While I guess the cron job should work, it might be more straightforward to just use an infinite loop in the bash script with sleep 60 at the end. Also makes it easier to stop ;). Very very cool, that LED strip light painting stuff!
- Halfgaar almost 11 years
  
  And then put that in /etc/rc.local
- user2914606 almost 11 years
  
  why don't you write a service file? it depends on what distribution you're using but that seems easier than using cron.
- nivek almost 11 years
  
  strugee, thanks. I was able to get some advice from friends and waded through the thick documentation for update-rc.d. IMHO the task of making sense of the dense SysV documentation is harder than a cron job (for a beginner!) :-) But in terms of functionality, yes, I agree with you that starting the program on startup makes more sense than running a redundant script every minute. (The cron option would have the advantage of auto-restarting the python code if it were to break---but we've already used this toy for several hours at a time with no problem, so hopefully that won't be needed!)
- nivek almost 11 years
  
  For future Googlers, for the record, I did not figure out why the Cron script didn't work.