You can preview your render interactively via RenderMan's Image Tool or Render View.
Using 'it' for Linux
Set your RMANFB environment variable to 'it' so the frame buffer will be pointing to 'it'.
setenv RMANFB it or export RMANFB=it depending on your shell.
- Set Display Device to Houdini Display (the default). If you change it to Framebuffer Device, it will also work.
Using 'it' for OSX/Windows
You don't need to set RMANFB. Simply set your Display Device to 'it'.
Pressing Render to MPlay will output your framebuffer directly to RenderMan's Image Tool (it).
The advantage of rendering to 'it' is prman outputs directly to the frame buffer without going through Houdini's imdisplay. So you will notice the render updating is faster than rendering in Render View. However, there may be some limitations, please consult the release notes for more information.
Using Render View
Go to Render View. Select your output, e.g. /out/ris5. And press Render.
The advantage of using Render View is you can view your AOV interactively and crop window works. See AOV Setup and Viewing.
To create a crop window, shift+left mouse drag to create the box. This currently only works in Render View.