Add NOTES paragraph noting that <sys/types.h> isn't required by

POSIX.1-2001 or Linux, but was required on some implementations.

man2/accept.2

@@ -39,7 +39,7 @@
 .SH NAME
 accept \- accept a connection on a socket
 .SH SYNOPSIS
-.B #include <sys/types.h>
+.BR "#include <sys/types.h>" "          /* See NOTES */"
 .br
 .B #include <sys/socket.h>
 .sp
@@ -255,6 +255,12 @@ of file status flags and always explicitly set all required flags on
 the socket returned from
 .BR accept ().
 .SH NOTES
+POSIX.1-2001 does not require the inclusion of
+.IR <sys/types.h> ,
+and this header file is not required on Linux.
+However, some historical (BSD) implementations required this header
+file, and portable applications are probably wise to include it.
+
 There may not always be a connection waiting after a
 .B SIGIO
 is delivered or

man2/bind.2

@@ -68,7 +68,7 @@
 bind \- bind a name to a socket
 .SH SYNOPSIS
 .nf
-.B #include <sys/types.h>
+.BR "#include <sys/types.h>" "          /* See NOTES */"
 .B #include <sys/socket.h>
 .sp
 .BI "int bind(int " sockfd ", const struct sockaddr *" my_addr \
@@ -230,6 +230,12 @@ function first appeared in 4.2BSD).
 .\" .B EISDIR
 .\" Unix-domain error conditions.
 .SH NOTES
+POSIX.1-2001 does not require the inclusion of
+.IR <sys/types.h> ,
+and this header file is not required on Linux.
+However, some historical (BSD) implementations required this header
+file, and portable applications are probably wise to include it.
+
 The third argument of
 .BR bind ()
 is in reality an

man2/connect.2

@@ -67,7 +67,7 @@
 connect \- initiate a connection on a socket
 .SH SYNOPSIS
 .nf
-.B #include <sys/types.h>
+.BR "#include <sys/types.h>" "          /* See NOTES */"
 .br
 .B #include <sys/socket.h>
 .sp
@@ -236,6 +236,12 @@ function first appeared in 4.2BSD), POSIX.1-2001.
 .\" It also
 .\" documents many additional error conditions not described here.
 .SH NOTES
+POSIX.1-2001 does not require the inclusion of
+.IR <sys/types.h> ,
+and this header file is not required on Linux.
+However, some historical (BSD) implementations required this header
+file, and portable applications are probably wise to include it.
+
 The third argument of
 .BR connect ()
 is in reality an

man2/gethostid.2

@@ -68,6 +68,19 @@ POSIX.1-2001 specifies
 .BR gethostid ()
 but not
 .BR sethostid ().
+.SH NOTES
+In the glibc implementation, if
+.BR gethostid ()
+cannot open
+.IR /etc/hostid ,
+then it obtains the host name using
+.BR gethostname (2),
+passes that host name to
+.BR gethostbyaddr (3)
+in order to obtain the host's IPv4 address,
+and returns a value obtained by bit-twiddling the IPv4 address.
+(This value may not be unique.)
+
 .SH "SEE ALSO"
 .BR hostid (1),
 .BR gethostbyname (3)

man2/getsockopt.2

@@ -44,7 +44,7 @@
 getsockopt, setsockopt \- get and set options on sockets
 .SH SYNOPSIS
 .nf
-.B #include <sys/types.h>
+.BR "#include <sys/types.h>" "          /* See NOTES */"
 .br
 .B #include <sys/socket.h>
 .sp
@@ -171,6 +171,12 @@ POSIX.1-2001.
 .\" .BR SO_SNDLOWAT ", " SO_RCVLOWAT ", " SO_SNDTIMEO ", " SO_RCVTIMEO
 .\" options
 .SH NOTES
+POSIX.1-2001 does not require the inclusion of
+.IR <sys/types.h> ,
+and this header file is not required on Linux.
+However, some historical (BSD) implementations required this header
+file, and portable applications are probably wise to include it.
+
 The
 .I optlen
 argument of

man2/listen.2

@@ -42,9 +42,13 @@
 .SH NAME
 listen \- listen for connections on a socket
 .SH SYNOPSIS
+.nf
+.BR "#include <sys/types.h>" "          /* See NOTES */"
+.br
 .B #include <sys/socket.h>
 .sp
 .BI "int listen(int " sockfd ", int " backlog );
+.fi
 .SH DESCRIPTION
 To accept connections, a socket is first created with
 .BR socket (2),
@@ -100,6 +104,12 @@ The
 .BR listen ()
 function call first appeared in 4.2BSD.
 .SH NOTES
+POSIX.1-2001 does not require the inclusion of
+.IR <sys/types.h> ,
+and this header file is not required on Linux.
+However, some historical (BSD) implementations required this header
+file, and portable applications are probably wise to include it.
+
 The behavior of the
 .I backlog
 parameter on TCP sockets changed with Linux 2.2.

man2/socket.2

@@ -42,7 +42,7 @@
 .SH NAME
 socket \- create an endpoint for communication
 .SH SYNOPSIS
-.B #include <sys/types.h>
+.BR "#include <sys/types.h>" "          /* See NOTES */"
 .br
 .B #include <sys/socket.h>
 .sp
@@ -324,6 +324,12 @@ It is generally portable to/from
 non-BSD systems supporting clones of the BSD socket layer (including
 System V variants).
 .SH NOTES
+POSIX.1-2001 does not require the inclusion of
+.IR <sys/types.h> ,
+and this header file is not required on Linux.
+However, some historical (BSD) implementations required this header
+file, and portable applications are probably wise to include it.
+
 The manifest constants used under 4.x BSD for protocol families
 are PF_UNIX, PF_INET, etc., while AF_UNIX etc. are used for address
 families.

man2/socketpair.2

@@ -40,7 +40,7 @@
 .SH NAME
 socketpair \- create a pair of connected sockets
 .SH SYNOPSIS
-.B #include <sys/types.h>
+.BR "#include <sys/types.h>" "          /* See NOTES */"
 .br
 .B #include <sys/socket.h>
 .sp
@@ -100,6 +100,12 @@ On Linux, the only supported domain for this call is
 (or synonymously,
 .BR AF_LOCAL ).
 (Most implementations have the same restriction.)
+
+POSIX.1-2001 does not require the inclusion of
+.IR <sys/types.h> ,
+and this header file is not required on Linux.
+However, some historical (BSD) implementations required this header
+file, and portable applications are probably wise to include it.
 .SH "SEE ALSO"
 .BR pipe (2),
 .BR read (2),