Table of Contents
cron-wrap
What is it?
“Obviously, you're not a golfer”. But you are probably a sysadmin.
The cwrap.py script is meant to be used as a wrapper for cron jobs. The idea here is that you use this script to wrap whatever would be a normal cronjob for you to perform functions based on what options are specified. I think this is best explained with an example.
I have a cronjob that runs every minute. First, I don't want “overlap”, a second instance is run while the first one is still running, if a single run takes a long time. Solved. The nature of my cronjob (just a script that is being run) is such that there will be an occasional failure, but an occasional failure, in this case, can be ignored. Instead, I only want to know when the script has failed 5 times in a row. Solved. By default, cwrap.py will also swallow all the output for the occasional fails, but I at least want a record of those failures so that I can determine whether the intermittent fails are happening more frequently and constitute a different problem. Solved (by turning on the syslog option).
This script may not be useful for everyone, but for some out there, it will save you a lot of time, effort and probably emails in your inbox.
Getting a Copy of it
If cron-wrap sounds like something you might be interested in, head over to the github page to download it, or clone the repository.
You can also install this via pip or easy_install.
pip install cron-wrap
NOTE: The RPMs are not guaranteed to be the latest versions. Check Github to find out what the latest version is. That said, I will try and keep these up to date.
Donations
By no means should anyone feel they have to donate. However, if you've used this stuff to save some time, prevent head shaped holes in the wall, raise your children or you just think this is awesome and want to contribute to my Surly fund (that stuff isn't cheap, but it's soooooo good), you can click the Paypal donate button below and toss me a couple of dollars. I've heard from others who have donated that they were visited by flying monkeys that spoke Icelandic, and were subsequently showered with fantastic gifts from said monkeys. I don't know if this is true, or if drug use was involved, but it still sounds pretty awesome.
<html> <form action=“https://www.paypal.com/cgi-bin/webscr” method=“post”> <input type=“hidden” name=“cmd” value=“_s-xclick”> <input type=“hidden” name=“hosted_button_id” value=“83ENX2ZV8E694”> <input type=“image” src=“https://www.paypalobjects.com/en_US/i/btn/btn_donateCC_LG.gif” border=“0” name=“submit” alt=“PayPal - The safer, easier way to pay online!”> <img alt=“” border=“0” src=“https://www.paypalobjects.com/en_US/i/scr/pixel.gif” width=“1” height=“1”> </form> </html>
Failures
The concept of a failure is simple. The exit code of the script that cwrap.py is running must be non-zero for cwrap.py to call it a “failure”.
Options
There are a plethora of options available here. See cwrap.py -h or man cwrap.py for the full lowdown.
Example
Here is a short example of how you would run a cron job with cwrap.py.
For the purpose of this example, we'll say that the normal cronjob is run as:
cron.sh -a do_stuff
Let's say that we always want to see the first failure in a string of failures (-f). Beyond the first failure, we don't want to be notified until the 10th consecutive failure (-n 10). This script can take a while to run so I want any other runs to retry two times (-r 2), but if it wasn't able to run because another instance was running, I don't want to hear about it (-i). I also don't want to see any normal output from it, but just when it fails (-q). Last, I want all errors to be logged to syslog (-S) under LOCAL1 (-C LOG_LOCAL1). Here would be the example:
cwrap.py -fSiq -n 10 -r 2 -C LOG_LOCAL1 cron.sh -a do_stuff