Change the built-in default socket directory to be /var/run/postgresql.
For backwards compatibility with (probably non-libpq-based) clients that
might still expect to find the socket in /tmp, also create a socket in
/tmp.  This is to resolve communication problems with clients operating
under systemd's PrivateTmp environment, which won't be using the same
global /tmp directory as the server; see bug #825448.

Note that we apply the socket directory change at the level of the
hard-wired defaults in the C code, not by just twiddling the setting in
postgresql.conf.sample; this is so that the change will take effect on
server package update, without requiring any existing postgresql.conf
to be updated.  (Of course, a user who dislikes this behavior can still
override it via postgresql.conf.)


diff --git a/contrib/pg_upgrade/test.sh b/contrib/pg_upgrade/test.sh
index 30bc527..4e8f6a4 100644
--- a/contrib/pg_upgrade/test.sh
+++ b/contrib/pg_upgrade/test.sh
@@ -107,6 +107,12 @@ done
 EXTRA_REGRESS_OPTS="$EXTRA_REGRESS_OPTS --port=$PGPORT"
 export EXTRA_REGRESS_OPTS
 
+# we want the Unix sockets in $temp_root
+PGHOST=$temp_root
+export PGHOST
+
+POSTMASTER_OPTS="$POSTMASTER_OPTS -c unix_socket_directories='$PGHOST'"
+
 # enable echo so the user can see what is being executed
 set -x
 
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index a055231..20b8c87 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2929,7 +2929,7 @@ static struct config_string ConfigureNamesString[] =
 		},
 		&Unix_socket_directories,
 #ifdef HAVE_UNIX_SOCKETS
-		DEFAULT_PGSOCKET_DIR,
+		DEFAULT_PGSOCKET_DIR ", /tmp",
 #else
 		"",
 #endif
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 5fc7291..d871341 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -1203,7 +1203,7 @@ setup_config(void)
 
 #ifdef HAVE_UNIX_SOCKETS
 	snprintf(repltok, sizeof(repltok), "#unix_socket_directories = '%s'",
-			 DEFAULT_PGSOCKET_DIR);
+			 DEFAULT_PGSOCKET_DIR ", /tmp");
 #else
 	snprintf(repltok, sizeof(repltok), "#unix_socket_directories = ''");
 #endif
diff --git a/src/include/pg_config_manual.h b/src/include/pg_config_manual.h
index 02bcd92..8aaf58b 100644
--- a/src/include/pg_config_manual.h
+++ b/src/include/pg_config_manual.h
@@ -144,7 +144,7 @@
  * here's where to twiddle it.  You can also override this at runtime
  * with the postmaster's -k switch.
  */
-#define DEFAULT_PGSOCKET_DIR  "/tmp"
+#define DEFAULT_PGSOCKET_DIR  "/var/run/postgresql"
 
 /*
  * The random() function is expected to yield values between 0 and
diff --git a/src/test/regress/pg_regress.c b/src/test/regress/pg_regress.c
index b632326..943165c 100644
--- a/src/test/regress/pg_regress.c
+++ b/src/test/regress/pg_regress.c
@@ -772,7 +772,7 @@ initialize_environment(void)
 		if (hostname != NULL)
 			doputenv("PGHOST", hostname);
 		else
-			unsetenv("PGHOST");
+			doputenv("PGHOST", "/tmp");
 		unsetenv("PGHOSTADDR");
 		if (port != -1)
 		{
@@ -2249,7 +2249,7 @@ regression_main(int argc, char *argv[], init_function ifunc, test_function tfunc
 		 */
 		header(_("starting postmaster"));
 		snprintf(buf, sizeof(buf),
-				 SYSTEMQUOTE "\"%s/postgres\" -D \"%s/data\" -F%s -c \"listen_addresses=%s\" > \"%s/log/postmaster.log\" 2>&1" SYSTEMQUOTE,
+				 SYSTEMQUOTE "\"%s/postgres\" -D \"%s/data\" -F%s -c \"listen_addresses=%s\" -c \"unix_socket_directories=/tmp\" > \"%s/log/postmaster.log\" 2>&1" SYSTEMQUOTE,
 				 bindir, temp_install,
 				 debug ? " -d 5" : "",
 				 hostname ? hostname : "",