Cron jobs research notes

  1. connect to server via SSH
  2. $ crontab -l to check cron jobs under current user
  3. $ crontab -e to edit cron table (note: if using vim, after the command above, enter i to insert content)
  4. * * * * * cd director && /user/bin/python3 test.py run this test.py python file once very minute
    (ref: Dillon Head’s post: beginners guid to cron)

    additionally:

  5. if you want to see the status: * * * * * cd director && /user/bin/python3 test.py >> test.out
  6. after the cron job has been executed: tail -f test.out to check the status if there’s anthing printed out from test.py file

Setting up for sending mail - django-mailer

Installation

(venv)$ pip install django-mailer

Settings.py

# settings.py

EMAIL_BACKEND = "mailer.backend.DbBackend"
# specify you are actually using django default mail backends to send emails
MAILER_EMAIL_BACKEND = 'django.core.mail.backends.smtp.EmailBackend'

EMAIL_USE_SSL = True
EMAIL_HOST = 'smtp.mail.ru'
EMAIL_PORT = 465
EMAIL_HOST_USER = 'example@email.com'
EMAIL_HOST_PASSWORD = 'email_psswd'
DEFAULT_FROM_EMAIL = 'Official Email <{}>'.format(EMAIL_HOST_USER)

bash command:

(venv)$ python manage.py send_mail

bash command ==> crontab -e

According to the official document, there should be a few cron jobs to be setup, including a send_mail command and 2 logging command:

*       * * * * (/path/to/your/python /path/to/your/manage.py send_mail >> ~/cron_mail.log 2>&1)
0,20,40 * * * * (/path/to/your/python /path/to/your/manage.py retry_deferred >> ~/cron_mail_deferred.log 2>&1)
0 0 * * * (/path/to/your/python /path/to/your/manage.py purge_mail_log 7 >> ~/cron_mail_purge.log 2>&1)

So edit the crontab:

$ crontab -e

Refer to the format below:

*/5 * * * * source /home/ubuntu/.bashrc && source /home/ubuntu/work/your-project/bin/activate && python /home/ubuntu/work/your-project/src/manage.py runcrons > /home/ubuntu/cronjob.log
# execute this command every 5 mins

An alternative way: DIY shell script

This SO post helped me to understand this

Basically, you create a text file and write a “shebang” and a couple command instead of writing everything in crontab:

  • the format of the script file (everything is a must)
    create a script file called script.sh 
      #!/bin/bash
  source /home/ubuntu/.bashrc
  source /home/ubuntu/project/venv/bin/activate
  python /home/ubuntu/project/manage.py send_mail >> /home/ubuntu/logs/cron_mail.log 2>&1
  • make your file executable 
      $ chmod +x script.sh
  • modify your path to add the directory where your script is located 
      $ export PATH=$PATH:/appropriate/directory

    Typically, you want $HOME/bin for storing your own scripts

Troubleshooting:

Checkout the Why crontab scripts are not working post

  • Cron not running 
      $ pgrep cron

    If you see no number, then cron is not running. sudo /etc/init.d/cron start can be used to start cron.

      $ sudo /etc/init.d/cron start
  [ ok ] Starting cron (via systemctl): cron.service.
  # OR
  $ sudo service cron start

    Also you could use systemctl in modern Linux, e.g.

      $ sudo systemctl start cron

    ### It seems that a new server just set up requires turning on cron manually.

  • Crontab file has to end in a new line.. it’s a silly one