The Free On-line Dictionary of Computing (30 December 2018):

ScumOS

    /skuhm'os/ or /skuhm'O-S/ An
   Unflattering hackerism for SunOS, the Unix variant once
   supported on Sun Microsystems's Unix workstations.

   Despite what this term might suggest, Sun was founded by
   hackers and still enjoys excellent relations with hackerdom;
   usage is more often in exasperation than outright loathing.

   See also sun-stools.  Compare AIDX, Macintrash, Nominal
   Semidestructor, Open DeathTrap, HP-SUX.

   [Jargon File]

   (1995-04-19)