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Cron and virtualenv

Posted by: admin November 1, 2017 Leave a comment

Questions:

I am trying to run a Django management command from cron. I am using virtualenv to keep my project sandboxed.

I have seen examples here and elsewhere that show running management commands from within virtualenv’s like:

0 3 * * * source /home/user/project/env/bin/activate && /home/user/project/manage.py command arg

However, even though syslog shows an entry when the task should have started, this task never actually runs (the log file for the script is empty). If I run the line manually from the shell, it works as expected.

The only way I can currently get the command to run via cron, is to break the commands up and put them in a dumb bash wrapper script:

#!/bin/sh
source /home/user/project/env/bin/activate
cd /home/user/project/
./manage.py command arg

Please enlighten me what the difference is. What am I missing?

Thanks

EDIT:

ars came up with a working combination of commands:

0 3 * * * cd /home/user/project && /home/user/project/env/bin/python /home/user/project/manage.py command arg

At least in my case, invoking the activate script for the virtualenv did nothing. This works, so on with the show.

Answers:

You should be able to do this by using the python in your virtual environment:

/home/my/virtual/bin/python /home/my/project/manage.py command arg

EDIT: If your django project isn’t in the PYTHONPATH, then you’ll need to switch to the right directory:

cd /home/my/project && /home/my/virtual/bin/python ...

You can also try to log the failure from cron:

cd /home/my/project && /home/my/virtual/bin/python /home/my/project/manage.py > /tmp/cronlog.txt 2>&1

Another thing to try is to make the same change in your manage.py script at the very top:

#!/home/my/virtual/bin/python

Questions:
Answers:

Running source from a cronfile won’t work as cron uses /bin/sh as its default shell, which doesn’t support source. You need to set the SHELL environment variable to be /bin/bash:

SHELL=/bin/bash
*/10 * * * * root source /path/to/virtualenv/bin/activate && /path/to/build/manage.py some_command > /dev/null

It’s tricky to spot why this fails as /var/log/syslog doesn’t log the error details. Best to alias yourself to root so you get emailed with any cron errors. Simply add yourself to /etc/aliases and run sendmail -bi.

More info here:
http://codeinthehole.com/archives/43-Running-django-cronjobs-within-a-virtualenv.html

Questions:
Answers:

Rather than mucking around with virtualenv-specific shebangs, just prepend PATH onto the crontab.

From an activated virtualenv, run these three commands and python scripts should just work:

$ echo "PATH=$PATH" > myserver.cron
$ crontab -l >> myserver.cron
$ crontab myserver.cron

The crontab’s first line should now look like this:

PATH=/home/me/virtualenv/bin:/usr/bin:/bin:  # [etc...]

Questions:
Answers:

The only correct way to run python cron jobs when using a virtualenv is to activate the environment and then execute the environment’s python to run your code.

One way to do this is use virtualenv’s activate_this in your python script, see: http://virtualenv.readthedocs.org/en/latest/userguide.html#using-virtualenv-without-bin-python

Another solution is echoing the complete command including activating the environment and piping it into /bin/bash. Consider this for your /etc/crontab:

***** root echo 'source /env/bin/activate; python /your/script' | /bin/bash

Questions:
Answers:

The best solution for me was to both

  • use the python binary in the venv bin/ directory
  • set the python path
    to include the venv modules directory.

man python mentions modifying the path in shell at $PYTHONPATH or in python with sys.path

Other answers mention ideas for doing this using the shell. From python, adding the following lines to my script allows me to successfully run it directly from cron.

import sys
sys.path.insert(0,'/path/to/venv/lib/python3.3/site-packages');

Here’s how it looks in an interactive session —

Python 3.3.2+ (default, Feb 28 2014, 00:52:16) 
[GCC 4.8.1] on linux
Type "help", "copyright", "credits" or "license" for more information.

>>> import sys

>>> sys.path
['', '/usr/lib/python3.3', '/usr/lib/python3.3/plat-x86_64-linux-gnu', '/usr/lib/python3.3/lib-dynload']

>>> import requests
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named 'requests'   

>>> sys.path.insert(0,'/path/to/venv/modules/');

>>> import requests
>>>