So, I'm trying to get the kernel message to output to both serial and the screen/keyboard. I found this message from @andyf omnios.org/ml-archive/2017-March/008447.html but it doesn't stay on the screen/keyboard once the OS is booted. Is there a way to get it on both? specifically, I'm looking for the messages on kernel panics so I can keep a buffer of them even if the machine reboots.

Once the OS is active, it only has a notion of a single primary console. It will not duplicate to both places.

If you are trying to capture kernel panics, I would recommend setting up a dump device to capture them.

if the primary console is serial, is there a way to make assign a login prompt to the screen/keyboard?

The easiest way is to enable the VT services -- svcadm enable vtdaemon '*console-login:vt*'

okay, thanks