Cron Jobs

In practice, meetup2xibo and summarize-m2x-logs run unattended as cron jobs.

Cron Setup

Cron runs jobs listed in a crontab file. This file must be edited with the crontab program:

$ crontab -e

The example cron jobs below are written for the bash shell. Add this line to the crontab to select that shell:

SHELL=/bin/bash

When a cron job produces any output to stdout or stderr (standard output and standard error, respectively), cron can send those results via email. Add this line to the crontab to specify the email recipient:

MAILTO=chris.jones@example.com

The cron jobs run meetup2xibo, summarize-m2x-logs, and yesterday, all programs installed by the meetup2xibo package. The which command will reveal where meetu2xibo and the other programs were installed:

$ which meetup2xibo
/home/joels/.virtualenvs/meetup2xibo/bin/meetup2xibo

Add this line to the crontab to extend the system path with the path to the meetup2xibo programs:

PATH=~/.virtualenvs/meetup2xibo/bin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

Meetup2xibo Cron Jobs

Cron runs meetup2xibo frequently to keep the agenda displays up-to-date with Meetup.com. Most events start on the hour, at a quarter past, or half past the hour, so run times are slightly offset ahead of event start times.

The following crontab line schedules ordinary meetup2xibo runs every 10 minutes:

3,13,23,33,43,53 * * * * cd ~/meetup2xibo && . ./meetup2xibo.env && meetup2xibo -w

The -w option directs warnings to standard error; cron will send them via email to the cron user. Meetup2xibo will log info and higher messages to the default meetup2xibo.log file.

Late each day, cron runs meetup2xibo with two extra options:

• -c to log schedule conflicts
• -m to log all location mappings from Meetup.com’s venue name and how-to-find-us fields to Xibo’s location

This run is scheduled to avoid the every-10-minute runs. The following crontab line schedules a schedule conflict and location mapping meetup2xibo run every night before midnight:

48 23 * * * cd ~/meetup2xibo && . ./meetup2xibo.env && meetup2xibo -w -c -m

Summarize-m2x-logs Cron Job

Cron runs summarize-m2x-logs early every morning to summarize the previous day’s meetup2xibo activity and mail the results to interested people. The time was chosen to take place after daily log rotation, to have low impact on computer resources, and to provide a morning email to administrators. The following crontab line schedules summarize-m2x-logs while administrators are sleeping:

44 1 * * * YESTERDAY=`yesterday` ; summarize-m2x-logs
-t "jmith@example.com events@example.com"
-s "Meetup to Xibo Summary for ${YESTERDAY}"
~/meetup2xibo/meetup2xibo.log.${YESTERDAY}
| ssmtp -t

These five lines must be combined into a single crontab line.

Yesterday’s date is saved in YESTERDAY for substituion later on the line. The -t option selects email-formatted output and provides a space-separated list of email recipients. The -s option provides the email subject with yesterday’s date inserted. Summarize-m2x-logs takes yesterday’s log file, ~/meetup2xibo/meetup2xibo.log.${YESTERDAY}, with yesterday’s date appended to the filename.

Cron pipes the email output to the sSMTP, a lightweight mail transport agent that handles only outbound emails. On a more capable computer, sendmail could be used instead.