[manual] Job control is no longer optional.

Job control was made mandatory in POSIX.1-2001: compare
<http://pubs.opengroup.org/onlinepubs/7990989775/xsh/unistd.h.html> with
<http://pubs.opengroup.org/onlinepubs/009695399/basedefs/unistd.h.html>.
Seventeen years later, we need not devote an entire manual @node to
warning people that this was once an optional POSIX feature.

	* manual/job.texi (Job Control is Optional): Remove node, as
	job control has not been optional in quite some time.
	(Job Control): Mention briefly that systems older than
	POSIX.1-2001 might not support job control.
	* manual/conf.texi (_POSIX_JOB_CONTROL): Will always be
	defined on systems conforming to POSIX.1-2001.

3 files changed, 20 insertions, 29 deletions

diff --git a/ChangeLog b/ChangeLog
index 19466c18db..7dea006c16 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2018-10-17  Zack Weinberg  <zackw@panix.com>
+
+	* manual/job.texi (Job Control is Optional): Remove node, as
+	job control has not been optional in quite some time.
+	(Job Control): Mention briefly that systems older than
+	POSIX.1-2001 might not support job control.
+	* manual/conf.texi (_POSIX_JOB_CONTROL): Will always be
+	defined on systems conforming to POSIX.1-2001.
+
 2018-10-17  Arjun Shankar  <arjun@redhat.com>
 
 	[BZ #22062]
diff --git a/manual/conf.texi b/manual/conf.texi
index dbd1d30287..f959b00bb6 100644
--- a/manual/conf.texi
+++ b/manual/conf.texi
@@ -156,6 +156,8 @@ supported; use @code{sysconf} to find out.  @xref{Sysconf}.
 If this symbol is defined, it indicates that the system supports job
 control.  Otherwise, the implementation behaves as if all processes
 within a session belong to a single process group.  @xref{Job Control}.
+Systems conforming to the 2001 revision of POSIX, or newer, will
+always define this symbol.
 @end deftypevr
 
 @deftypevr Macro int _POSIX_SAVED_IDS
diff --git a/manual/job.texi b/manual/job.texi
index 944967a73d..e304313ca7 100644
--- a/manual/job.texi
+++ b/manual/job.texi
@@ -19,9 +19,15 @@ You need to be familiar with concepts relating to process creation
 Handling}) in order to understand this material presented in this
 chapter.
 
+@vindex _POSIX_JOB_CONTROL
+Some old systems do not support job control, but @gnusystems{} always
+have, and it is a required feature in the 2001 revision of POSIX.1
+(@pxref{POSIX}).  If you need to be portable to old systems, you can
+use the @code{_POSIX_JOB_CONTROL} macro to test at compile-time
+whether the system supports job control.  @xref{System Options}.
+
 @menu
 * Concepts of Job Control::     Jobs can be controlled by a shell.
-* Job Control is Optional::     Not all POSIX systems support job control.
 * Controlling Terminal::        How a process gets its controlling terminal.
 * Access to the Terminal::      How processes share the controlling terminal.
 * Orphaned Process Groups::     Jobs left after the user logs out.
@@ -29,7 +35,7 @@ chapter.
 * Functions for Job Control::   Functions to control process groups.
 @end menu
 
-@node Concepts of Job Control, Job Control is Optional,  , Job Control
+@node Concepts of Job Control
 @section Concepts of Job Control
 
 @cindex shell
@@ -102,30 +108,7 @@ jobs between foreground and background.
 @xref{Access to the Terminal}, for more information about I/O to the
 controlling terminal.
 
-@node Job Control is Optional, Controlling Terminal, Concepts of Job Control , Job Control
-@section Job Control is Optional
-@cindex job control is optional
-
-Not all operating systems support job control.  @gnusystems{} do
-support job control, but if you are using @theglibc{} on some other
-system, that system may not support job control itself.
-
-You can use the @code{_POSIX_JOB_CONTROL} macro to test at compile-time
-whether the system supports job control.  @xref{System Options}.
-
-If job control is not supported, then there can be only one process
-group per session, which behaves as if it were always in the foreground.
-The functions for creating additional process groups simply fail with
-the error code @code{ENOSYS}.
-
-The macros naming the various job control signals (@pxref{Job Control
-Signals}) are defined even if job control is not supported.  However,
-the system never generates these signals, and attempts to send a job
-control signal or examine or specify their actions report errors or do
-nothing.
-
-
-@node Controlling Terminal, Access to the Terminal, Job Control is Optional, Job Control
+@node Controlling Terminal
 @section Controlling Terminal of a Process
 
 One of the attributes of a process is its controlling terminal.  Child
@@ -1166,9 +1149,6 @@ The @code{setpgid} function puts the process @var{pid} into the process
 group @var{pgid}.  As a special case, either @var{pid} or @var{pgid} can
 be zero to indicate the process ID of the calling process.
 
-This function fails on a system that does not support job control.
-@xref{Job Control is Optional}, for more information.
-
 If the operation is successful, @code{setpgid} returns zero.  Otherwise
 it returns @code{-1}.  The following @code{errno} error conditions are
 defined for this function: