Attempt #1: fix permission bits?
Did not work.
Same problem as originally.
Running as "root" (sido):


KLH10# devdef dsk0 rh0.0 rp     type=rp06 format=dbd9 path=../../out/klh10/rp0.dsk iodly=0
[dp_init: shmget failed - 12]
RPXX subproc init failed!
Final init of device "dsk0" failed!

==============================================================
*** tools/klh10/src/dpsup.c.~1~	2021-06-26 06:33:23.000000000 -0400
--- tools/klh10/src/dpsup.c	2021-06-26 06:45:19.000000000 -0400
*************** int dp_init(register struct dp_s *dp, si
*** 115,121 ****
      }
  
      /* Create a shared mem seg.  Set perms to owner-only RW. */
!     if ((shmid = shmget(IPC_PRIVATE, (u_int)totsiz, 0600)) == -1) {
  	fprintf(stderr, "[dp_init: shmget failed - %d]\r\n", errno);
  	return FALSE;
      }
--- 115,121 ----
      }
  
      /* Create a shared mem seg.  Set perms to owner-only RW. */
!     if ((shmid = shmget(IPC_PRIVATE, (u_int)totsiz, S_IRUSR | S_IWUSR)) == -1) {
  	fprintf(stderr, "[dp_init: shmget failed - %d]\r\n", errno);
  	return FALSE;
      }
==============================================================