PTYs

There is a configuration option which asks the backend driver to ask the remote host to assign the connection a pty. A pty is a pseudo-terminal, which in effect means tell the backend that this is an interactive session. This is normally a bad idea.

Most of the differences are best explained by this page from the author of rbenv.

When Capistrano makes a connection it is a non-login, non-interactive shell. This was not an accident!

It’s often used as a band aid to cure issues related to RVM and rbenv not loading login and shell initialisation scripts. In these scenarios RVM and rbenv are the tools at fault, or at least they are being used incorrectly.

Whilst, especially in the case of language runtimes (Ruby, Node, Python and friends in particular) there is a temptation to run multiple versions in parallel on a single server and to switch between them using environmental variables, this is an anti-pattern, and symptomatic of bad design (e.g. you’re testing a second version of Ruby in production because your company lacks the infrastructure to test this in a staging environment).