Using shush as a crontab wrapper

Apr 11, 2015   #cron 

Cron is a great tool for linux servers, but it's a very limited in it's capabilities (since it follows the Unix philosophy), so when I started to run up against those limits, I began doing all sorts of bash trickery to accomplish what I needed to happen, but that swiftly started giving me even more problem. At work, I use the Jenkins CI tool as a cron replacement (great tool, allows for distributed runs, queuing tasks, emails on failure, etc), but it seemed rather heavy weight for a homelab. Thankfully, there are a lot of cron wrappers/replacements out there, but I settled on shush, a neat little wrapper script for cron.

There are a couple reasons I like it:

  • The ability to manually run scripts under shush before adding them to cron
  • Automatic crontab management
  • Simple C binary, very few dependencies
  • Text based config file
  • Locking and timeout handling

Basically how it works is that there's a designated directory that holds all the shush configuration files. These files can be named anything, although I usually have them be extensionless for simplicity. You can then run any of these files with shush -c <directory> <config_file_name>. If you use the default directory of $HOME/.shush/, you can just run shush <config_file_name>. However, in order to have the config file run regularly, you need to set the schedule setting, and run shush -c <directory> -u to update the crontab file.

The man page has some more documentation, but I'll at least break down the example config file to make it more understandable.

Set the command shush -c /etc/shush -u to run every day at 9 PM:

command=shush -c /etc/shush -u
schedule=0 9 * * *

Use a lockfile. If a lockfile already exists, send an email to root and root-logs, then abort the job:

lock=notify=root root-logs,abort

Send out an email notification if the script is still running after 5 minutes, but keep the script alive:

timeout=5m,notify=root root-logs

Print stderr output first, use the text format, and set the email subject:

stderr=first
format=text
Subject=Crontab Daily Update

Always send an email to root-logs:

[logs]
to=root-logs

If one of the various failure conditions applies, send an email to root:

[readers]
if=$exit != 0 || $outlines != 1 || $errsize > 0 || U
to=root
format=rich

Shush is a very powerful tool, and I'm very happy with the ways that I've been able to implement it in my homelab. However, it can be a bit confusing for a beginner, and the regexp matching features leave much to be desired. With the intention of fixing things up, I've create a repository at https://github.com/smuth4/shush, which I can hopefully use to clean up things, and get the project active again. Feel free to compile, try out and maybe even contribute to this neat little tool!