--- postgresql-15.2/src/bin/pg_upgrade/option.c	2023-03-07 23:37:50.271950638 +0100
+++ postgresql-15.2/src/bin/pg_upgrade/option.c	2023-03-07 23:40:28.343899006 +0100
@@ -445,8 +445,14 @@
 get_sock_dir(ClusterInfo *cluster, bool live_check)
 {
 #if defined(HAVE_UNIX_SOCKETS) && !defined(WIN32)
-	if (!live_check)
+	if (!live_check) {
 		cluster->sockdir = user_opts.socketdir;
+#ifndef UNIX_PATH_MAX
+#define UNIX_PATH_MAX 108
+#endif
+		if (strlen(cluster->sockdir) >= UNIX_PATH_MAX - sizeof(".s.PGSQL.50432"))
+			strcpy(cluster->sockdir, "/tmp"); /* fall back to tmp */
+	}
 	else
 	{
 		/*
--- postgresql-15.2/src/include/pg_config_manual.h	2023-03-07 23:37:50.153949183 +0100
+++ postgresql-15.2/src/include/pg_config_manual.h	2023-03-07 23:38:28.898426739 +0100
@@ -224,7 +224,7 @@
  * support them yet.
  */
 #ifndef WIN32
-#define DEFAULT_PGSOCKET_DIR  "/tmp"
+#define DEFAULT_PGSOCKET_DIR  "/var/run/postgresql"
 #else
 #define DEFAULT_PGSOCKET_DIR ""
 #endif