Why is su using a different ruby version compared to when I'm logged in as the actual user?

Question

I'm trying to deploy a Ruby on Rails application using nginx and unicorn. When I try to run my unicorn init script, I get the following error:

$ sudo service rails_app start
Starting rails_app
-su: bundle: command not found

It fails to run on this command:

su - complab -c "bundle exec unicorn -c config/unicorn.rb -E production -D"

However, running unicorn manually while logged in as $USER works just fine:

$ bundle exec unicorn -c config/unicorn.rb -E production

I have verified that the path set on the init script is correct. On further investigation, I discovered that while $USER has ruby version 2.2.0 installed via rbenv, running su - $USER -c "ruby -v" shows that it's running on 1.9.3.

I have already run rbenv global 2.2.0 but still it doesn't work.

I thought su meant I was able to temporarily changing the user who owns the session? Why is it that su $USER shows a different ruby version from when I am actually logged in as $USER?

Hope you can help me out!

Answer 1

The reason is that sudo doesn't preserve environment variable. And since rbenv is using user environment it doesn't work out of the box. You can use a command like this to run ruby with sudo:

ruby=`which ruby` && sudo $ruby -v

If you want to run unicorn under the user you have installed rbenv into you have to change these to match your app:

!/bin/sh

### BEGIN INIT INFO
# Provides:          unicorn
# Required-Start:    $local_fs $remote_fs
# Required-Stop:     $local_fs $remote_fs
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: starts unicorn
# Description:       starts uniconr using start-stop-daemon
### END INIT INFO

set -u
set -e

export PATH=/path/to/rbenv/bin:$PATH
export RBENV_DIR=/path/to/rbenv
export RBENV_ROOT=/path/to/rbenv

APP_ROOT=/path/to/rack_app/root
PID=$APP_ROOT/tmp/pids/unicorn.pid
RAILS_ENV=production

export PATH="$RBENV_ROOT/shims:$RBENV_ROOT/rbenv:$PATH"
CMD="bundle exec $RBENV_ROOT/shims/unicorn -D -E $RAILS_ENV -c config/unicorn/$RAILS_ENV.rb"


old_pid="$PID.oldbin"

cd $APP_ROOT || exit 1

sig () {
    test -s "$PID" && kill -$1 `cat $PID`
}

oldsig () {
    test -s $old_pid && kill -$1 `cat $old_pid`
}

case $1 in
start)
    sig 0 && echo >&2 "Already running" && exit 0
    $CMD
    ;;
stop)
    sig QUIT && exit 0
    echo >&2 "Not running"
    ;;
force-stop)
    sig TERM && 0
    echo >&2 "Not running"
    ;;
restart|reload)
    sig HUP && echo reloaded OK && exit 0
    echo >&2 "Couldn't reload, starting '$CMD' instead"
    $CMD
    ;;
upgrade)
    sig USR2 && exit 0
    echo >&2 "Couldn't upgrade, starting '$CMD' instead"
    ;;
rotate)
    sig USR1 && echo rotated logs OK && exit 0
    echo >&2 "Couldn't rotate logs" && 1
    ;;
*)
    echo >&2 "Usage $0 <start|stop|restart|upgrade|rotate|force-stop>"
    exit 1
    ;;
esac