nss: Make nsswitch.conf more distribution friendly.

The current default nsswitch.conf file provided by glibc is not very
distribution friendly. The file contains some minimal directives that no
real distribution uses. This update aims to provide a rich set of
comments which are useful for all distributions, and a broader set of
service defines which should work for all distributions.

Tested defaults on x86_64 and they work. The nsswitch.conf file more
closely matches what we have in Fedora now, and I'll adjust Fedora to
use this version with minor changes to enable Fedora-specific service
providers.

v2
- Add missing databases to manual.
- Add link to manual from default nsswitch.conf.
- Sort nsswitch.conf according to most used database first.

v3
- Only mention implemented services in 'NSS Basics.'
- Mention 'automount' in 'Services in the NSS configuration.'
- Sort services in alphabetical order.

v4
- Project name is 'Samba'.

v5
- Fix typo in manual/nss.texi.

v6
- Fix another typo in manual/nss.texi. Ran spell checker this time.

ChangeLog

@@ -1,3 +1,9 @@
+2019-08-19  Carlos O'Donell  <carlos@redhat.com>
+
+	* nss/nsswitch.conf: Expand comments, and simplify defaults.
+	* manual/nss.texi (NSS Basics): List all known databases.
+	(Services in the NSS configuration): Mention automount.
+
 2019-08-19  Florian Weimer  <fweimer@redhat.com>
 
 	Do not print backtraces on fatal errors.

manual/nss.texi

@@ -56,13 +56,17 @@ functions to access the databases.
 @noindent
 The databases available in the NSS are
 
+@cindex aliases
 @cindex ethers
 @cindex group
+@cindex gshadow
 @cindex hosts
+@cindex initgroups
 @cindex netgroup
 @cindex networks
-@cindex protocols
 @cindex passwd
+@cindex protocols
+@cindex publickey
 @cindex rpc
 @cindex services
 @cindex shadow
@@ -75,16 +79,22 @@ Ethernet numbers,
 @comment @pxref{Ethernet Numbers}.
 @item group
 Groups of users, @pxref{Group Database}.
+@item gshadow
+Group passphrase hashes and related information.
 @item hosts
 Host names and numbers, @pxref{Host Names}.
+@item initgroups
+Supplementary group access list.
 @item netgroup
 Network wide list of host and users, @pxref{Netgroup Database}.
 @item networks
 Network names and numbers, @pxref{Networks Database}.
-@item protocols
-Network protocols, @pxref{Protocols Database}.
 @item passwd
 User identities, @pxref{User Database}.
+@item protocols
+Network protocols, @pxref{Protocols Database}.
+@item publickey
+Public keys for Secure RPC.
 @item rpc
 Remote procedure call names and numbers.
 @comment @pxref{RPC Database}.
@@ -96,8 +106,8 @@ User passphrase hashes and related information.
 @end table
 
 @noindent
-There will be some more added later (@code{automount}, @code{bootparams},
-@code{netmasks}, and @code{publickey}).
+@c We currently don't implement automount, netmasks, or bootparams.
+More databases may be added later.
 
 @node NSS Configuration File, NSS Module Internals, NSS Basics, Name Service Switch
 @section The NSS Configuration File
@@ -159,6 +169,10 @@ these files since they should be placed in a directory where they are
 found automatically.  Only the names of all available services are
 important.
 
+Lastly, some system software may make use of the NSS configuration file
+to store their own configuration for similar purposes.  Examples of this
+include the @code{automount} service which is used by @code{autofs}.
+
 @node Actions in the NSS configuration, Notes on NSS Configuration File, Services in the NSS configuration, NSS Configuration File
 @subsection Actions in the NSS configuration
 

nss/nsswitch.conf

@@ -1,20 +1,69 @@
+#
 # /etc/nsswitch.conf
 #
-# Example configuration of GNU Name Service Switch functionality.
+# An example Name Service Switch config file. This file should be
+# sorted with the most-used services at the beginning.
 #
+# Valid databases are: aliases, ethers, group, gshadow, hosts,
+# initgroups, netgroup, networks, passwd, protocols, publickey,
+# rpc, services, and shadow.
+#
+# Valid service provider entries include (in alphabetical order):
+#
+#	compat			Use /etc files plus *_compat pseudo-db
+#	db			Use the pre-processed /var/db files
+#	dns			Use DNS (Domain Name Service)
+#	files			Use the local files in /etc
+#	hesiod			Use Hesiod (DNS) for user lookups
+#	nis			Use NIS (NIS version 2), also called YP
+#	nisplus			Use NIS+ (NIS version 3)
+#
+# See `info libc 'NSS Basics'` for more information.
+#
+# Commonly used alternative service providers (may need installation):
+#
+#	ldap			Use LDAP directory server
+#	myhostname		Use systemd host names
+#	mymachines		Use systemd machine names
+#	mdns*, mdns*_minimal	Use Avahi mDNS/DNS-SD
+#	resolve			Use systemd resolved resolver
+#	sss			Use System Security Services Daemon (sssd)
+#	systemd			Use systemd for dynamic user option
+#	winbind			Use Samba winbind support
+#	wins			Use Samba wins support
+#	wrapper			Use wrapper module for testing
+#
+# Notes:
+#
+# 'sssd' performs its own 'files'-based caching, so it should generally
+# come before 'files'.
+#
+# WARNING: Running nscd with a secondary caching service like sssd may
+# 	   lead to unexpected behaviour, especially with how long
+# 	   entries are cached.
+#
+# Installation instructions:
+#
+# To use 'db', install the appropriate package(s) (provide 'makedb' and
+# libnss_db.so.*), and place the 'db' in front of 'files' for entries
+# you want to be looked up first in the databases, like this:
+#
+# passwd:    db files
+# shadow:    db files
+# group:     db files
 
-passwd:		db files
-group:		db files
-initgroups:	db [SUCCESS=continue] files
-shadow:		db files
-gshadow:	files
-
-hosts:		files dns
-networks:	files dns
-
-protocols:	db files
-services:	db files
-ethers:		db files
-rpc:		db files
-
-netgroup:	db files
+# In alphabetical order. Re-order as required to optimize peformance.
+aliases:    files
+ethers:     files
+group:      files
+gshadow:    files
+hosts:      files dns
+initgroups: files
+netgroup:   files
+networks:   files dns
+passwd:     files
+protocols:  files
+publickey:  files
+rpc:        files
+shadow:     files
+services:   files