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

systems programmer
systems programming

    (sysprog) A generic job title that covers a variety of
   specialist roles such as writing low-level code that talks to
   directly to the operating system on a server.

   Typical skills required are experience of specific operating
   systems, networking (TCP/IP, ATM, Ethernet, DNS),
   electronic mail (POP, IMAP, SMTP), web servers,
   RDBMS, operating system and network security, and hardware
   (SCSI, hard disks, and backup devices).

   Contrast: system administration.

   (1999-09-14)