9696 add /etc/system.d support
Portions contributed by: Andy Fiddaman <andy@omniosce.org>
Reviewed by: Hans Rosenfeld <hans.rosenfeld@joyent.com>
Reviewed by: Peter Tribble <peter.tribble@gmail.com>
Reviewed by: C Fraire <cfraire@me.com>
Reviewed by: Toomas Soome <tsoome@me.com>

*** 9,18 ****
--- 9,36 ----
         The system file is used for customizing the operation of the operating
         system kernel. The recommended procedure is to preserve the original
         system file before modifying it.
  
  
+        It is not recommended to edit the /etc/system file directly but rather
+        to deliver configuration fragments into files under /etc/system.d;
+        files in this directory are combined in alphabetical order and read by
+        the kernel before /etc/system is processed. Directives in /etc/system
+        therefore take precedence over any settings delivered in fragment
+        files.
+ 
+ 
+        The recommended naming schema for the fragment files is to use the name
+        of the package which is delivering the file with '/' characters
+        replaced by ':'; file names that start with a dot (.) will be ignored.
+ 
+ 
+        If /etc/system.d/ exists and contains any fragment files, then the
+        directory must also be writable or it will not be possible to create or
+        update the system boot archive.
+ 
+ 
         The system file contains commands which are read by the kernel during
         initialization and used to customize the operation of your system.
         These commands are useful for modifying the system's treatment of its
         loadable kernel modules.
  
*** 235,244 ****
         locate a system file that will work, you may specify /dev/null. This
         acts as an empty system file, and the system will attempt to boot using
         its default settings.
  
  NOTES
!        The /etc/system file is read only once, at boot time.
  
  
  
!                                January 25, 2016                      SYSTEM(4)
--- 253,262 ----
         locate a system file that will work, you may specify /dev/null. This
         acts as an empty system file, and the system will attempt to boot using
         its default settings.
  
  NOTES
!        The system files are read only once, at boot time.
  
  
  
!                                January 29, 2019                      SYSTEM(4)