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)
@@ -82,10 +82,15 @@
 	fi
 fi
 
+# If the firstboot sentinel doesn't exist, we want to skip firstboot scripts.
+if ! [ -e ${firstboot_sentinel} ]; then
+	skip_firstboot="-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
 #
-files=`rcorder ${skip} /etc/rc.d/* 2>/dev/null`
+files=`rcorder ${skip} ${skip_firstboot} /etc/rc.d/* 2>/dev/null`
 
 _rc_elem_done=' '
 for _rc_elem in ${files}; do
@@ -107,7 +112,13 @@
 *)	find_local_scripts_new ;;
 esac
 
-files=`rcorder ${skip} /etc/rc.d/* ${local_rc} 2>/dev/null`
+# The firstboot sentinel might be on a newly mounted filesystem; look for it
+# again and unset skip_firstboot if we find it.
+if [ -e ${firstboot_sentinel} ]; then
+	skip_firstboot=""
+fi
+
+files=`rcorder ${skip} ${skip_firstboot} /etc/rc.d/* ${local_rc} 2>/dev/null`
 for _rc_elem in ${files}; do
 	case "$_rc_elem_done" in
 	*" $_rc_elem "*)	continue ;;
@@ -116,6 +127,15 @@
 	run_rc_script ${_rc_elem} ${_boot}
 done
 
+# Remove the firstboot sentinel, and reboot if it was requested.
+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