Capistrano - cannot find ruby

Question

Its confusing. I've gone through the documentation, I know capistrano uses a non-login, non-interactive shell.

So I have this simple task

desc 'Echo environment vars'
namespace :env do
  task :echo do
    on roles(:app) do
      execute 'echo $PATH'
      execute 'printenv'
      execute 'echo $PATH'
      execute '/usr/bin/env ruby --version'
    end
  end
end

Run cap production env:echo

The output is this

DEBUG[558ffc94] Running /usr/bin/env [ ! -d ~/.rbenv/versions/2.1.5 ] on mycompany.com
DEBUG[558ffc94] Command: [ ! -d ~/.rbenv/versions/2.1.5 ]
DEBUG[558ffc94] Finished in 7.972 seconds with exit status 1 (failed).
INFO[c9043b5c] Running /usr/bin/env echo $PATH on mycompany.com
DEBUG[c9043b5c] Command: echo $PATH
INFO[c9043b5c] Finished in 0.211 seconds with exit status 0 (successful).
DEBUG[c9043b5c]         /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
INFO[c9043b5c] Finished in 0.211 seconds with exit status 0 (successful).
INFO[7a765d1d] Running /usr/bin/env printenv on mycompany.com
DEBUG[7a765d1d] Command: ( PATH=$HOME/.rbenv/shims:$HOME/.rbenv/bin:$PATH RBENV_ROOT=~/.rbenv RBENV_VERSION=2.1.5 /usr/bin/env printenv )
DEBUG[7a765d1d]         RBENV_VERSION=2.1.5
DEBUG[7a765d1d]         RBENV_ROOT=/home/deployer/.rbenv
DEBUG[7a765d1d]         PATH=/home/deployer/.rbenv/shims:/home/deployer/.rbenv/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
DEBUG[7a765d1d]         XDG_SESSION_ID=159
DEBUG[7a765d1d]         TERM=xterm
DEBUG[7a765d1d] 
DEBUG[7a765d1d]         SHELL=/bin/bash
DEBUG[7a765d1d]         SSH_CLIENT=172.16.10.10 51174 22
DEBUG[7a765d1d]         SSH_TTY=/dev/pts/3
DEBUG[7a765d1d]         USER=deployer
DEBUG[7a765d1d] 
DEBUG[7a765d1d]         SSH_AUTH_SOCK=/tmp/ssh-OtFWklQB4e/agent.7579
DEBUG[7a765d1d]         MAIL=/var/mail/deployer
DEBUG[7a765d1d]         PWD=/home/deployer
DEBUG[7a765d1d]         LANG=en_US.UTF-8
DEBUG[7a765d1d]         SHLVL=1
DEBUG[7a765d1d]         HOME=/home/deployer
DEBUG[7a765d1d]         LOGNAME=deployer
DEBUG[7a765d1d]         SSH_CONNECTION=172.16.10.10 51174 172.16.10.55
DEBUG[7a765d1d]         LC_CTYPE=en_US.UTF-8
DEBUG[7a765d1d]         XDG_RUNTIME_DIR=/run/user/1001
DEBUG[7a765d1d]         _=/usr/bin/env
INFO[7a765d1d] Finished in 0.228 seconds with exit status 0 (successful).
INFO[461230a4] Running /usr/bin/env echo $PATH on mycompany.com
DEBUG[461230a4] Command: echo $PATH
INFO[461230a4] Finished in 0.209 seconds with exit status 0 (successful).
DEBUG[461230a4]         /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
INFO[461230a4] Finished in 0.209 seconds with exit status 0 (successful).
INFO[0d327934] Running /usr/bin/env /usr/bin/env ruby --version on mycompany.com
DEBUG[0d327934] Command: /usr/bin/env ruby --version
cap aborted!
SSHKit::Runner::ExecuteError: Exception while executing on host mycompany.com: /usr/bin/env ruby --version exit status: 127
/usr/bin/env ruby --version stdout: Nothing written
/usr/bin/env ruby --version stderr: Nothing written
config/deploy.rb:253:in `block (3 levels) in <top (required)>'
SSHKit::Command::Failed: /usr/bin/env ruby --version exit status: 127
/usr/bin/env ruby --version stdout: Nothing written
/usr/bin/env ruby --version stderr: Nothing written
config/deploy.rb:253:in `block (3 levels) in <top (required)>'
Tasks: TOP => env:echo
(See full trace by running task with --trace)

I notice that printenv shows a different PATH and echoing $PATH shows something different. Why?

Next, why is "/usr/bin/env ruby --version" failing?

I try replacing "execute '/usr/bin/env ruby --version'" with "execute 'which ruby'", I get "SSHKit::Command::Failed: which ruby exit status: 1"

I give it the whole path - "execute '/usr/bin/which ruby'", same result - "SSHKit::Command::Failed: /usr/bin/which ruby exit status: 1"

What is going on? Why isn't the PATH shown with "printenv" being picked up?

Thanks for helping clarify.

Answer 1

This is nicely explained in the sshkit gem command map section:

It's often a problem that programmatic SSH sessions don't have the same environment variables as interactive sessions.

A problem often arises when calling out to executables expected to be on the $PATH. Under conditions without dotfiles or other environmental configuration, $PATH may not be set as expected, and thus executables are not found where expected.

Btw. just to make clear - capistrano uses sshkit as its backend.

As for the high-level approach to capistrano, I'd recommend just using capistrano-rbenv + capistrano-rbenv-install gems (disclaimer, I wrote the latter one).

With these 2 gems, all you need is to have ruby version specified, for example:

# in config/deploy.rb
set :rbenv_ruby, '2.0.0-p247'

And everything else should just work smoothly! Even the exact ruby version will be installed to the server if necessary, so that the user doesn't have to fiddle with it.