Add BACKENDS section in slapd.conf(5).

Briefly compare back-bdb and back-ldbm.
Remove mention of MDBM and NDBM.  Rename GNU DBM to GDBM.
Fix spacing typos.  Prefix an octal file mode with 0.
Mention "notags" (new name for "nolang" from the attribute options patch).
Add SEE ALSO slapd-monitor(5) to slapd.conf(5).

doc/man/man5/slapd-bdb.5

@@ -10,9 +10,11 @@ ETCDIR/slapd.conf
 The BDB backend to
 .BR slapd (8)
 is the recommended backend for a normal slapd database.
+However, it takes more care than with the LDBM backend to configure
+it properly.
 It uses the Sleepycat Berkeley DB (BDB) package to store data.
 It makes extensive use of indexing and caching to speed data access.
-.TP
+.LP
 It is noted that these options are intended to complement
 Berkeley DB configuration options set in the environment's
 .B DB_CONFIG
@@ -130,4 +132,4 @@ Berkeley DB configuration file
 .BR slapadd (8),
 .BR slapcat (8),
 .BR slapindex (8),
-.BR Berkeley DB documentation .
+Berkeley DB documentation.

doc/man/man5/slapd-ldbm.5

@@ -9,8 +9,10 @@ ETCDIR/slapd.conf
 .SH DESCRIPTION
 The LDBM backend to
 .BR slapd (8)
-is a database which uses one of BerkeleyDB, GNU DBM, MDBM or NDBM to
-store data.
+is the database backend which is easiest to configure.
+However, it does not offer the data durability features of the BDB
+backend.
+It uses Berkeley DB or GDBM to store data.
 It makes extensive use of indexing and caching to speed data access.
 .SH CONFIGURATION
 These
@@ -102,8 +104,11 @@ can be decomposed into
 .B subfinal
 indices.
 The special type
-.B nolang
-may be specified to disallow use of this index by language subtypes.
+.B notags
+(or
+.BR nolang )
+may be specified to disallow use of this index by subtypes with tagging
+options (such as language options).
 The special type
 .B nosubtypes
 may be specified to disallow use of this index by named subtypes.

doc/man/man5/slapd.conf.5

@@ -1098,9 +1098,72 @@ is asked to modify a replicated local database.
 If specified multiple times, each url is provided.
 .SH DATABASE-SPECIFIC OPTIONS
 Each database may allow specific configuration options; they are
-documented separately in the
+documented separately in the backends' manual pages.
+.SH BACKENDS
+The following backends can be compiled into slapd.
+They are documented in the
 .BR slapd-<backend> (5)
 manual pages.
+.TP
+.B bdb
+This is the recommended backend for a normal slapd database.
+However, it takes more care than with the LDBM backend to configure
+it properly.
+It uses the Sleepycat Berkeley DB (BDB) package to store data.
+.TP
+.B ldbm
+This is the database backend which is easiest to configure.
+However, it does not offer the data durability features of the BDB
+backend.
+It uses Berkeley DB or GDBM to store data.
+.TP
+.B dnssrv
+This backend is experimental.
+It serves up referrals based upon SRV resource records held in the
+Domain Name System.
+.TP
+.B ldap
+This backend acts as a proxy to forward incoming requests to another
+LDAP server.
+.TP
+.B meta
+This backend performs basic LDAP proxying with respect to a set of
+remote LDAP servers.
+It is an enhancement of the ldap backend.
+.TP
+.B monitor
+This backend provides information about the running status of the slapd
+daemon.
+.TP
+.B null
+Operations in this backend succeed but do nothing.
+.TP
+.B passwd
+This backend is provided for demonstration purposes only.
+It serves up user account information from the system
+.BR passwd (5)
+file.
+.TP
+.B perl
+This backend embeds a
+.BR perl (1)
+interpreter into slapd.
+It runs Perl subroutines to implement LDAP operations.
+.TP
+.B shell
+This backend executes external programs to implement LDAP operations.
+It is is primarily intended to be used in prototypes.
+.TP
+.B sql
+This backend is experimental.
+It services LDAP requests from an SQL database.
+.TP
+.B tcl
+This backend is experimental.
+It embeds a
+.BR Tcl (3tcl)
+interpreter into slapd.
+It runs Tcl commands to implement LDAP operations.
 .SH EXAMPLES
 .LP
 Here is a short example of a configuration file:
@@ -1120,7 +1183,7 @@ database  bdb
 suffix    "dc=our-domain,dc=com"
 # The database directory MUST exist prior to
 # running slapd AND should only be accessible
-# by the slapd/tools. Mode 700 recommended.
+# by the slapd/tools. Mode 0700 recommended.
 directory LOCALSTATEDIR/openldap-data
 # Indices to maintain
 index     objectClass  eq
@@ -1149,6 +1212,7 @@ default slapd configuration file
 .BR slapd-ldap (5),
 .BR slapd-ldbm (5),
 .BR slapd-meta (5),
+.BR slapd-monitor (5),
 .BR slapd-null (5),
 .BR slapd-passwd (5),
 .BR slapd-perl (5),