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/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c

index 9481f2d..75532c7 100644

--- a/src/backend/utils/misc/guc.c

+++ b/src/backend/utils/misc/guc.c

@@ -3196,7 +3196,7 @@ 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 feeff9e..3e3d784 100644

--- a/src/bin/initdb/initdb.c

+++ b/src/bin/initdb/initdb.c

@@ -1234,7 +1234,7 @@ 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 e278fa0..9ee15d4 100644

--- a/src/include/pg_config_manual.h

+++ b/src/include/pg_config_manual.h

@@ -169,7 +169,7 @@

  * 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"

 /*

  * This is the default event source for Windows event log.