Partial backport of the following Fedora Rawhide patches:
    
commit a747c093bbee95a3bdf1d7ef052bd248c95fadc5
Author: Florian Weimer <fweimer@redhat.com>
Date:   Fri Jun 1 12:05:26 2018 +0200
    
    Modernise nsswitch.conf defaults (#1581809)
    
(backported the line which adds sss description).
    
commit 82a97343d6405772541d754aeb4bab79612bd839
Author: Carlos O'Donell <carlos@redhat.com>
Date:   Thu Feb 7 17:15:12 2019 -0500
    
    Add warnings and notes to /etc/nsswitch.conf and /etc/nscd.conf.
    
(backported fully with adjustments for releng/nsswitch.conf).

diff --git a/nscd/nscd.conf b/nscd/nscd.conf
index 3730835c50a349c4..d7c0ee590466b0d4 100644
--- a/nscd/nscd.conf
+++ b/nscd/nscd.conf
@@ -3,6 +3,9 @@
 #
 # An example Name Service Cache config file.  This file is needed by nscd.
 #
+# WARNING: Running nscd with a secondary caching service like sssd may lead to
+#          unexpected behaviour, especially with how long entries are cached.
+#
 # Legal entries are:
 #
 #	logfile			<file>
@@ -22,7 +25,12 @@
 #       suggested-size		<service> <prime number>
 #	check-files		<service> <yes|no>
 #	persistent		<service> <yes|no>
+#
 #	shared			<service> <yes|no>
+#	NOTE: Setting 'shared' to a value of 'yes' will accelerate the lookup
+#	      with the help of the client, but these lookups will not be
+#	      counted as cache hits i.e. 'nscd -g' may show '0%'.
+#
 #	max-db-size		<service> <number bytes>
 #	auto-propagate		<service> <yes|no>
 #
diff --git a/releng/nsswitch.conf b/releng/nsswitch.conf
index 0a02e5717d906387..4b120bf9e6f94e5f 100644
--- a/releng/nsswitch.conf
+++ b/releng/nsswitch.conf
@@ -19,8 +19,11 @@
 #	db			Use the local database (.db) files
 #	compat			Use NIS on compat mode
 #	hesiod			Use Hesiod for user lookups
+#	sss			Use sssd (System Security Services Daemon)
 #	[NOTFOUND=return]	Stop searching if not found so far
 #
+# WARNING: Running nscd with a secondary caching service like sssd may lead to
+# 	   unexpected behaviour, especially with how long entries are cached.
 
 # To use db, put the "db" in front of "files" for entries you want to be
 # looked up first in the databases