Actualize documentation about file descriptors

Better explain limits, with a link to the Solaris documentation.
Improve wording and actualize the numbers for current systems.

doc/pod/inn.conf.pod

@@ -652,7 +652,7 @@ C<tradindexed>, and this is set to a value other than C<0>, INN will keep
 around and open that many recently written-to overview files in case more
 articles come in for those newsgroups.  Every overview cache slot consumes
 two file descriptors, so be careful not to set this value too high.  You
-may be able to use the C<limit> command to see how many open file
+may be able to use the C<ulimit -n> command to see how many open file
 descriptors your operating system allows.  innd(8) also uses an open file
 descriptor for each incoming feed and outgoing channel or batch file, and
 if it runs out of open file descriptors, it may throttle and stop accepting
@@ -1560,8 +1560,8 @@ If set to anything other than C<0>, maximum buffer size (in bytes) for
 reading NNTP command will have this value.  It should not be large on
 systems which are slow to process and store articles, as that would lead
 to innd(8) spending a long time on each channel and keeping other channels
-waiting.  The default value is BUFSIZ defined in stdio.h (C<1024> in most
-environments, see setbuf(3)).
+waiting.  The default value is BUFSIZ defined in stdio.h (usually between
+C<1024> and C<8192> in most environments, see setbuf(3)).
 
 =item I<maxforks>
 
@@ -1619,15 +1619,20 @@ innd closes it.  The default value is C<3600> (an hour).
 The maximum number of file descriptors that innd(8) or innfeed(8) can have
 open at once.  If innd(8) or innfeed(8) attempts to open more file
 descriptors than this value, it is possible the program may throttle or
-otherwise suffer reduced functionality.  The number of open file
-descriptors is roughly the maximum number of incoming feeds and outgoing
+otherwise malfunction or suffer reduced functionality.  The number of open
+file descriptors is roughly the maximum number of incoming feeds and outgoing
 batches for innd(8) and the number of outgoing streams for innfeed(8).  If
 this parameter is set to a negative value, the default limit of the
 operating system will be used; this will normally be adequate on systems
 other than Solaris.  Nearly all operating systems have some hard maximum
-limit beyond which this value cannot be raised, usually either 128, 256,
-or 1024.  The default value of this parameter is C<-1>.  Setting it to
-C<256> on Solaris systems is highly recommended.
+limit beyond which this value cannot be raised, usually either 256, 1024,
+or 65536.  The default value of this parameter is C<-1>.
+
+Setting this parameter to C<256> on Solaris systems is highly
+recommended for 32-bit Solaris versions prior to 11.4, or 64-bit
+Solaris versions prior to 11.0.  See the L<Solaris documentation about file
+descriptors|https://support.oracle.com/knowledge/Sun%20Microsystems/1005979_1.html>
+for more details.
 
 =back
 

doc/pod/innfeed.conf.pod

@@ -337,9 +337,11 @@ If the value is greater than zero, then whenever a network socket file
 descriptor is created and it has a value I<less than> this, the file
 descriptor will be dup'ed to bring the value up greater than this.  This is
 to leave lower numbered file descriptors free for stdio.  Certain systems,
-Sun's in particular, require this.  SunOS 4.1.x usually requires a value
-of 128 and Solaris requires a value of 256.  The default if this is not
-specified, is C<0>.
+Sun's in particular, require this.  SunOS 4.1.x usually requires a value of
+128, 32-bit Solaris versions prior to 11.4 and 64-bit Solaris versions prior
+to 11.0 require a value of 256.  See the L<Solaris documentation about file
+descriptors|https://support.oracle.com/knowledge/Sun%20Microsystems/1005979_1.html>
+for more details.  The default if this is not specified, is C<0>.
 
 =back
 

doc/pod/install.pod

@@ -1679,33 +1679,32 @@ And it is also a good practice to refresh each day INN's cached IP addresses:
 
     30 2 * * * <pathbin in inn.conf>/ctlinnd -t 120 -s reload incoming.conf 'flush cache'
 
-
 =head1 File Descriptor Limits
 
 INN likes to use a lot of file descriptors, particularly if you have a lot
 of peers.  Depending on what your system defaults are, you may need to
 make sure the default limit is increased for INN (particularly for B<innd>
-and B<innfeed>).  This is vital on Solaris, which defaults (at least as of
-2.6) to an absurdly low limit of 64 file descriptors per process.
-
-One way to increase the number of file descriptors is to set
-I<rlimitnofile> in F<inn.conf> to a higher value.  This will cause B<innd>
-and B<innfeed> to try to increase the file descriptor limits when they
-start.  Note, however, that INN won't be able to increase the limits above
-the hard limits set by your operating system; on some systems, that hard
-limit is normally 256 file descriptors (Linux, for example).  On others,
-like Solaris, it's 1024.  Increasing the limit beyond that value may
-require serious system configuration work.  (On some operating systems, it
-requires patching and recompiling the kernel.  On Solaris it can be
-changed in F</etc/system>, but for 2.6 or earlier the limit cannot be
-increased beyond 1024 without breaking select(2) and thereby breaking all
-of INN.  For current versions of Linux, you may be able to change the
-maximum by writing to F</proc/sys/fs/file-max>.)
+and B<innfeed>).  This is vital on Solaris, which defaults to an absurdly
+low limit of 64 file descriptors per process up to Solaris 7, and 256 up to
+Solaris 11.4 SRU 26 included.
+
+One way to increase the number of file descriptors is to set I<rlimitnofile>
+in F<inn.conf> to a higher value.  This will cause B<innd> and B<innfeed> to
+try to increase the file descriptor limits when they start.  Note, however,
+that INN won't be able to increase the limits above the hard limits set by
+your operating system, usually either 256, 1024, or 65536 (see the value
+of C<FD_SETSIZE> in the F<sys/select.h> system header).  Increasing the
+limit beyond that value may require serious system configuration work.
+(On some operating systems, it requires patching and recompiling the kernel.
+On Solaris, it can be changed in F</etc/system>, but for 2.6 or earlier the
+limit cannot be increased beyond 1024 without breaking select(2) and thereby
+breaking all of INN.  For current versions of Linux, you may be able to change
+the maximum with the C<ulimit -n> command.)
 
 256 file descriptors will probably be enough for all but the largest
 sites.  There is no harm in setting the limits higher than you actually
 need (provided they're set to something lower than or equal to your system
-hard limit).  C<256> is therefore a reasonable value to try.
+hard limit).  C<256> or C<1024> are therefore reasonable values to try.
 
 If you're installing INN on a Solaris system, particularly if you're
 installing it on a dedicated news server machine, it may be easier to just