@reboot cronjob not executing

问题:

I have a Python script which simply writes some text and saves it to a file

#! /usr/bin/python3
def main():
     filename = '/home/user/testHello.txt'
     openfile = open(filename,"w")
     print("Hello CRON", file = openfile)
if __name__ == "__main__":
     main();

I want to execute this script at startup via CRON. So I edit the crontab listing by using

>crontab -e

My entire crontab looks like :

SHELL = /bin/bash
PATH = /sbin:/bin:/usr/sbin:/usr/bin
MAILTO = root
HOME = /
# run-parts
1 * * * * /home/user/tester.py
@reboot /home/user/tester.py

This is the location of the file, and the file has permissions to execute. I can run the file no problem as a script from the commandline. Yet when I restart the machine, no file is generated. I am trying to understand why, and played around with the crontab entry.

@reboot /usr/bin/python3 /home/user/tester.py

This didn't work either.

Edit:

ps aux | grep crond 

gives me

user     2259 0.0 0.0.  9436  948 pts/0 S+ 23:39   0:00 grep --color=auto crond

I am unsure how to check if crond is running, or if the user in question is mounted before/after CRON. I'll try with:

sudo crontab -e 

but that hasn't worked either.

Running:

pgrep cron

returns 957

回答1:

Mark Roberts pointed out a few things I'd done wrong.

Namely, the spaces here

MAIL = root
HOME = /

Get rid of those spaces..

Next, having Cron configuration fixed to email every minute.. instead of what I had :

*/1 * * * * /home/user/tester.py

Seems to me Lubuntu doesn't support the @Reboot Cron syntax.

回答2:

From what I've discovered just now, the @reboot syntax seems to depend on what crontab you're editing. I found that for the system-level /etc/cron.d/ folder, entries there must have a user, just like regular time-based crons.

Thus this worked for me, on Ubuntu 14.04, to run the specified command as root on startup:

@reboot root /home/vagrant/log.sh

回答3:

I've had a similar problem with a @reboot cron job not running; in case it helps anyone else:

The problem for me is that my home directory is encrypted with eCryptfs (which is what you get if you choose to encrypt your home directory when installing Ubuntu) - broadly speaking this means that the contents of your home directory aren't available until you log in, but cron runs @reboot jobs on reboot, not when you log in.

回答4:

I managed to get @reboot working with the answer @halfer provided, but want to add an interesting abstract from man 5 crontab

... The format of a cron command is very much the V7 standard, with a number of upward-compatible extensions. Each line has five time and date fields, followed by a command, followed by a newline character ('\n'). The system crontab (/etc/crontab) uses the same format, except that the username for the command is specified after the time and date fields and before the command. The fields may be separated by spaces or tabs. The maximum permitted length for the command field is 998 characters. ...

So you might check these as well in case the job is still not running.