man options(4) tells as; 

     options COMPAT_ULTRIX
     On those architectures that support it, this enables binary compatibility
     with Ultrix applications built for the same architecture.  This currently
     is limited to the pmax.  The functionality of this option is unknown.

It's a discouraging statement for ULTRIX lover(s).  'struct emul' is
one of proud accomplishments of NetBSD.  Can anybody figure out (and
comfirm) what NetBSD/pmax ULTRIX emulation can do or can't do?  It'd
also helpful to have 'howtos' to prepare /emul/ultrix environment
refering to the existense of /usr/share/sample/emul/ultrix/svc.conf.
How about emul.ultrix(5)?

The option should automagically enable options EXEC_ECOFF, or
prossibly other COMPAT_oldbsds.

Tohru Nishimura