diff --git a/contrib/pg_upgrade/check.c b/contrib/pg_upgrade/check.c
new file mode 100644
index 0fec73e..e7574a2
*** a/contrib/pg_upgrade/check.c
--- b/contrib/pg_upgrade/check.c
*************** output_check_banner(bool *live_check)
*** 29,40 ****
  	if (user_opts.check && is_server_running(old_cluster.pgdata))
  	{
  		*live_check = true;
- 		if (old_cluster.port == DEF_PGUPORT)
- 			pg_log(PG_FATAL, "When checking a live old server, "
- 				   "you must specify the old server's port number.\n");
- 		if (old_cluster.port == new_cluster.port)
- 			pg_log(PG_FATAL, "When checking a live server, "
- 				   "the old and new port numbers must be different.\n");
  		pg_log(PG_REPORT, "Performing Consistency Checks on Old Live Server\n");
  		pg_log(PG_REPORT, "------------------------------------------------\n");
  	}
--- 29,34 ----
*************** check_cluster_compatibility(bool live_ch
*** 291,296 ****
--- 285,300 ----
  		new_cluster.controldata.cat_ver < TABLE_SPACE_SUBDIRS_CAT_VER)
  		pg_log(PG_FATAL, "This utility can only upgrade to PostgreSQL version 9.0 after 2010-01-11\n"
  			   "because of backend API changes made during development.\n");
+ 
+ 	/* We read the real port number for PG >= 9.1 */
+ 	if (GET_MAJOR_VERSION(old_cluster.major_version) < 901 &&
+ 		old_cluster.port == DEF_PGUPORT)
+ 			pg_log(PG_FATAL, "When checking a pre-PG 9.1 live old server, "
+ 				   "you must specify the old server's port number.\n");
+ 
+ 	if (old_cluster.port == new_cluster.port)
+ 		pg_log(PG_FATAL, "When checking a live server, "
+ 			   "the old and new port numbers must be different.\n");
  }
  
  
diff --git a/contrib/pg_upgrade/option.c b/contrib/pg_upgrade/option.c
new file mode 100644
index 94bce50..e511839
*** a/contrib/pg_upgrade/option.c
--- b/contrib/pg_upgrade/option.c
*************** adjust_data_dir(ClusterInfo *cluster)
*** 376,378 ****
--- 376,439 ----
  
  	check_ok();
  }
+ 
+ 
+ /*
+  * get_sockdir_and_live_port
+  *
+  * Set the socket directory to either the configured location (live check)
+  * or the current directory, and live port number.
+  */
+ void
+ get_sockdir_and_live_port(bool live_check)
+ {
+ 	if (!live_check)
+ 	{
+ #ifdef HAVE_UNIX_SOCKETS
+ 		/* Use the current directory for the socket */
+ 		if (!getcwd(os_info.sockdir, MAXPGPATH))
+ 			pg_log(PG_FATAL, "cannot find current directory\n");
+ #endif
+ 	}
+ 	/* port/sockdir added to the 4th/5th line of postmaster.pid in PG 9.1 */
+ 	else if (GET_MAJOR_VERSION(old_cluster.major_version) >= 901)
+ 	{
+ 		/* get live port number and sockdir */
+ 
+ 		char		filename[MAXPGPATH], line[MAXPGPATH];
+ 		FILE		*fp;
+ 		int			i;
+ 		unsigned short orig_old_port = old_cluster.port;
+ 
+ 		snprintf(filename, sizeof(filename), "%s/postmaster.pid", old_cluster.pgdata);
+ 		if ((fp = fopen(filename, "r")) == NULL)
+ 			pg_log(PG_FATAL, "Cannot open file %s: %m\n", filename);
+ 	
+ 		for (i = 0; i < 5; i++)
+ 		{
+ 			if (fgets(line, sizeof(line), fp) == NULL)
+ 				pg_log(PG_FATAL, "Cannot read line %d from %s: %m\n", i + 1, filename);
+ 			/* potentially overwrite user-supplied value */
+ 			if (i == 3)
+ 				sscanf(line, "%hu", &old_cluster.port);
+ #ifdef HAVE_UNIX_SOCKETS
+ 			if (i == 4)
+ 				/* strip off newline */
+ 				sscanf(line, "%s\n", os_info.sockdir);
+ #endif
+ 		}
+ 
+ 		/* warn of port number correction */
+ 		if (old_cluster.port != orig_old_port && orig_old_port != DEF_PGUPORT)
+ 			pg_log(PG_WARNING, "User-supplied old port number %hu corrected to %hu\n",
+ 			orig_old_port, old_cluster.port);
+ 			
+ 		fclose(fp);
+ 	}
+ 
+ #ifdef HAVE_UNIX_SOCKETS
+ 	if (strlen(os_info.sockdir) != 0)
+ 		/* For client communication */
+ 		pg_putenv("PGHOST", os_info.sockdir);
+ #endif
+ }
diff --git a/contrib/pg_upgrade/pg_upgrade.c b/contrib/pg_upgrade/pg_upgrade.c
new file mode 100644
index c47c8bb..6b41559
*** a/contrib/pg_upgrade/pg_upgrade.c
--- b/contrib/pg_upgrade/pg_upgrade.c
*************** main(int argc, char **argv)
*** 86,96 ****
  	setup(argv[0], live_check);
  
  	check_cluster_versions();
  	check_cluster_compatibility(live_check);
  
  	check_old_cluster(live_check, &sequence_script_file_name);
  
- 
  	/* -- NEW -- */
  	start_postmaster(&new_cluster);
  
--- 86,97 ----
  	setup(argv[0], live_check);
  
  	check_cluster_versions();
+ 	get_sockdir_and_live_port(live_check);
+ 
  	check_cluster_compatibility(live_check);
  
  	check_old_cluster(live_check, &sequence_script_file_name);
  
  	/* -- NEW -- */
  	start_postmaster(&new_cluster);