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I have a Rails runner task that I want to run from cron, but of course cron runs as root and so the environment is set up improperly to get RVM to work properly. I've tried a number of things and none have worked thus far. The crontab entry is:

*  0 * * * root cd /home/deploy/rails_apps/supercharger/current/ && /usr/local/rvm/wrappers/ruby-1.9.3-p484/ruby bundle exec rails runner -e production "Charger.start"

Apologies for the super long command line. Anyhow, the error I'm getting from this is:

ruby: No such file or directory -- bundle (LoadError)

So ruby is being found in the RVM directory, but again, the environment is wrong.

I tried rvm alias delete [alias_name] and it seemed to do something, but darn if I know where the wrapper it generated went. I looked in /usr/local/rvm/wrappers and didn't see one with the name I had specified.

This seems like a common problem -- common enough that the whenever gem exists. The runner command I'm using is so simple, it seemed like a slam dunk to just put this entry in the crontab and go, but not so much...

Any help with this is appreciated.

Steve Ross
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2 Answers2

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You can run cron as different user than root. Even in your example the task begins with

*  0 * * * root cd

root is the user that runs the command. You can edit it with crontab -e -u username.

If you insist on running cron task as root or running as other user does not work for some reason, you can switch user with su. For example:

su - username -c "bundle exec rails runner -e production "Charger.start"
katafrakt
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  • I did try `0 * 0 0 0 0 deploy big_long_command_string` but it failed to respect the RVM settings. There's some magic I may have missed. I believe `whenever` may be a cheap solution but it obviously doesn't cover up the personal blind spot I obviously have in this case. – Steve Ross Oct 05 '14 at 22:12
  • That's why actually the second method may be better. Cron jobs run in `sh`, not `bash` by default and you probably don't have RVM configured with `sh` (I don't know if it's even possible). You could try to change shell to `bash` (see: http://unix.stackexchange.com/questions/94456/how-to-change-cron-shell-sh-to-bash) but then you would probably need to manually source some files like `.bash_profile` or wherever is RVM configured. – katafrakt Oct 06 '14 at 06:28
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It sounds like you could use a third-party tool to tether your Rails app to cron: Whenever. You already know about it, but it seems you never tried it. This gem includes a simple DSL that could be applied in your case like:

every :day # Or specify another period, or something else, see README
  runner "Charger.start"
end

Once you've defined your schedule, you'll need to write it into crontab with whenever command line utility. See README file and whenever --help for details.

It should not cause any performance impact at runtime since all it does is conversion into crontab format upon deployment or explicit command. It's not needed, once the server is running, everything is done by cron after that.

If you don't want an extra gem anyway, you might as well check what command does it issue for executing your task. Still, an automated way of adding a cron task is easier to maintain and to deploy. Sure, just tossing a line into the crontab is easier — just for you and just this once. Then it starts to get repetitive and tiring, not to mention confusion for other potential developers who will have to set up something similar on their own machines.

D-side
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  • To speed this process up, I went with `whenever` and after deploy, ssh'ed into the server and ran the `whenever` command. I copied and pasted into my crontab. At some point, I may want to incorporate this into my deploy, but not right now... Once the job is running reliably, then the extra automation step. Thanks! – Steve Ross Oct 05 '14 at 22:09