cd to symbolically linked directory fails in cron environment

Question

I have a server running Ubuntu 12.04, which we use to host a Rails app. I'm running a task on cron, which is made up of a couple of unix commands separated by && - e.g:

cd /home/deploy/app/current && RAILS_ENV=production ...

The final bit has been snipped, as the command is failing on the very first cd, with this:

cd: No such file or directory

In the deploy user's environment that cd works without a problem. The directory exists, and it's a symbolic link:

lrwxrwxrwx 1 deploy deploy 42 Mar  4 15:28 /home/deploy/app/current -> /home/deploy/app/releases/20130304152305

I thought it was strange that the ability for the shell to cd to a symbolic link would be affected by the environment, so I spit out the cron's environment variables to a file, according to this question: How to simulate the environment cron executes a script with?.

If I try and execute that line as the cron user, it fails:

$ env - $(cat ~/cron.env) cd /home/deploy/app/current
env: cd: No such file or directory

Why does this happen? The cron's environment variables are:

HOME=/home/deploy
LOGNAME=deploy
PATH=/usr/bin:/bin
LANG=en_US.UTF-8
SHELL=/bin/sh
PWD=/home/deploy

Answer 1

cd is a shell builtin, not an program, and so neither cron nor env cannot execute it directly. The following should work for your cron job:

sh -c "cd /home/deploy/app/current && RAILS_ENV=production ..."