Index: etc/defaults/rc.conf
===================================================================
--- etc/defaults/rc.conf	(revision 256432)
+++ etc/defaults/rc.conf	(working copy)
@@ -619,6 +619,9 @@
 accounting_enable="NO"	# Turn on process accounting (or NO).
 ibcs2_enable="NO"	# Ibcs2 (SCO) emulation loaded at startup (or NO).
 ibcs2_loaders="coff"	# List of additional Ibcs2 loaders (or NO).
+firstboot_sentinel="/firstboot"	# Scripts with "firstboot" keyword are run if
+			# this file exists.  Should be on a R/W filesystem so
+			# the file can be deleted after the boot completes.
 
 # Emulation/compatibility services provided by /etc/rc.d/abi
 sysvipc_enable="NO"	# Load System V IPC primitives at startup (or NO).
Index: etc/rc
===================================================================
--- etc/rc	(revision 256432)
+++ etc/rc	(working copy)
@@ -81,6 +81,9 @@
 		skip="$skip -s nojailvnet"
 	fi
 fi
+if ! [ -e ${firstboot_sentinel} ]; then
+	skip="$skip -s firstboot"
+fi
 
 # Do a first pass to get everything up to $early_late_divider so that
 # we can do a second pass that includes $local_startup directories
@@ -116,6 +119,13 @@
 	run_rc_script ${_rc_elem} ${_boot}
 done
 
+if [ -e ${firstboot_sentinel} ]; then
+	rm ${firstboot_sentinel}
+	if [ -e ${firstboot_sentinel}-reboot ]; then
+		rm ${firstboot_sentinel}-reboot
+		kill -INT 1
+	fi
+fi
 echo ''
 date
 exit 0