Creating socket in /tmp is silly, but unfortunately it's default location,
so many clients expect it. Thus we preconfigure PostgreSQL to create socket
both in /run/postgresql and /tmp.
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -63,7 +63,7 @@
 #port = 5432				# (change requires restart)
 #max_connections = 100			# (change requires restart)
 #superuser_reserved_connections = 3	# (change requires restart)
-#unix_socket_directories = '/tmp'	# comma-separated list of directories
+unix_socket_directories = '/run/postgresql,/tmp'	# comma-separated list of directories
 					# (change requires restart)
 #unix_socket_group = ''			# (change requires restart)
 #unix_socket_permissions = 0777		# begin with 0 to use octal notation