cron rbenv bundle exec rake task

keywords: cron, crontab, Ubuntu 14.04, rbenv, RACK_ENV, RAILS_ENV, Ruby 2.2.2, Rails backgroud job

The example

Let say we have a deploy user and we want to have an automated rake task execution that would proces some events every minute.

We could use whenever gem or some other gem altering crontab or behaving similar to cron (daemons gem) but this project is too small or VM has too litle memory or project is too not-important so we want to keep it simple.

Our server deploy user already has rbenv installed (http://www.eq8.eu/blogs/4-installing-rbenv-on-ubuntu-machine) and we already have our project in folder ~/apps/myapp

The task that we want cron to process is RACK_ENV=production bundle exec rake event:process

note: RACK_ENV is similar to RAILS_ENV. In my example I’m using simple Sinatra app therefore I’m passing RACK_ENV to ActiveRecord::Base

Set up cron

To setup cron job for user deploy you do:

crontab -u deploy -e

And we add:

* * * * * PATH=$PATH:/usr/local/bin && bash -lc "cd /home/deploy/apps/myapp && RACK_ENV=production bundle exec rake event:process"

Obviously the * * * * * is a crontab scheduling syntax (run something every minute) and you can learn abaut the values anywhere (e.g. http://kvz.io/blog/2007/07/29/schedule-tasks-on-linux-using-crontab/), this is outside the topic of our article.

But why all those command arguments ? Well it’s tricky.

You see, apparently cron has limited access to $PATH and doesn’t know about your user’s bash configuration (it’s not triggering as bash env).

So you need to extend the PATH and then trigger your command via bash -lc which will load .bash_profile therefore your ands rbenv location and furtherly extends $PATH with rbenv. bash -lc executes only one command that’s why the remaining part is in quotes " "

From what I’ve seen playing around with our curl example (but I may be wrong on this) because we load the .bash_profile the ENV changes yet again therefore RACK_ENV=production (or RAILS_ENV=production) must be inside the quotes othervise it’s not going to be passed to rake.

note: Of course you can setup cron on whatever user or as a global cron job (crontab -e) but then your rbenv needs to be installed globaly on system not on a user.

.bash_profile is not the same as .bashrc

if you have lines:

export RBENV_ROOT="${HOME}/.rbenv"

if [ -d "${RBENV_ROOT}" ]; then
  export PATH="${RBENV_ROOT}/bin:${PATH}"
  eval "$(rbenv init -)"
fi

… in .bashrc and not in .bash_profile this will not work (unless your .bash_profile is loading bashrc. The reason is (like I said before) bash -lc loads .bash_profile context.

To solve this either load .bash_profile form .bashrc or other way around.

# in .bashrc
. ~/.bash_profile

cron log

If you need further debugging what is going worng check:

grep CRON /var/log/syslog
tail -f /var/log/syslog

Even more cron rbenv debugging

For me helpfull was to add something like this to crontab:

* * * * * PATH=$PATH:/usr/local/bin && bash -lc "cd /home/deploy/apps/myapp && RACK_ENV=production bundle exec rake event:process > /tmp/lets_figure_this_out.txt"

To check what ENV variables are actually set:

* * * * * bash -lc "env > /tmp/env.txt"

…and check if you have something like this

PATH=/home/app/.rbenv/shims:/home/app/.rbenv/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin:/home/app/bin

Just please remember to remove those lines when you’re finished

Last note

I’m not an expert on Cron or Bash I’m just a Ruby developer trying to get stuff done. I may be wrong on some stuff mentioned in here, please correct me in comment or make a Pull Request to the article.

https://github.com/equivalent/scrapbook2/blob/master/archive/blogs/2015-07-02-cronntab-rbenv-bundle-exec-rake-task.md