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 -up postgresql-13.0/src/include/pg_config_manual.h.patch1 postgresql-13.0/src/include/pg_config_manual.h

--- postgresql-13.0/src/include/pg_config_manual.h.patch1	2020-10-23 10:18:12.204959024 +0200

+++ postgresql-13.0/src/include/pg_config_manual.h	2020-10-23 10:18:39.391208931 +0200

@@ -201,7 +201,7 @@

  * support them yet.

  */

 #ifndef WIN32

-#define DEFAULT_PGSOCKET_DIR  "/tmp"

+#define DEFAULT_PGSOCKET_DIR  "/var/run/postgresql"

 #else

 #define DEFAULT_PGSOCKET_DIR ""

 #endif