Install some simple defenses in postmaster startup to help ensure a useful

error message if the installation directory layout is messed up (or at least,
something more useful than the behavior exhibited in bug #4787).  During
postmaster startup, check that get_pkglib_path resolves as a readable
directory; and if ParseTzFile() fails to open the expected timezone
abbreviation file, check the possibility that the directory is missing rather
than just the specified file.  In case of either failure, issue a hint
suggesting that the installation is broken.  These two checks cover the lib/
and share/ trees of a full installation, which should take care of most
scenarios where a sysadmin decides to get cute.

src/backend/postmaster/postmaster.c

@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.577 2009/04/05 04:19:58 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.578 2009/05/02 22:02:37 tgl Exp $
  *
  * NOTES
  *
@@ -315,6 +315,7 @@ extern int	optreset;			/* might not be declared by system headers */
 /*
  * postmaster.c - function prototypes
  */
+static void getInstallationPaths(const char *argv0);
 static void checkDataDir(void);
 
 #ifdef USE_BONJOUR
@@ -493,11 +494,8 @@ PostmasterMain(int argc, char *argv[])
 											  ALLOCSET_DEFAULT_MAXSIZE);
 	MemoryContextSwitchTo(PostmasterContext);
 
-	if (find_my_exec(argv[0], my_exec_path) < 0)
-		elog(FATAL, "%s: could not locate my own executable path",
-			 argv[0]);
-
-	get_pkglib_path(my_exec_path, pkglib_path);
+	/* Initialize paths to installation files */
+	getInstallationPaths(argv[0]);
 
 	/*
 	 * Options setup
@@ -690,15 +688,6 @@ PostmasterMain(int argc, char *argv[])
 		ExitPostmaster(1);
 	}
 
-#ifdef EXEC_BACKEND
-	/* Locate executable backend before we change working directory */
-	if (find_other_exec(argv[0], "postgres", PG_BACKEND_VERSIONSTR,
-						postgres_exec_path) < 0)
-		ereport(FATAL,
-				(errmsg("%s: could not locate matching postgres executable",
-						progname)));
-#endif
-
 	/*
 	 * Locate the proper configuration files and data directory, and read
 	 * postgresql.conf for the first time.
@@ -1062,6 +1051,58 @@ PostmasterMain(int argc, char *argv[])
 }
 
 
+/*
+ * Compute and check the directory paths to files that are part of the
+ * installation (as deduced from the postgres executable's own location)
+ */
+static void
+getInstallationPaths(const char *argv0)
+{
+	DIR		   *pdir;
+
+	/* Locate the postgres executable itself */
+	if (find_my_exec(argv0, my_exec_path) < 0)
+		elog(FATAL, "%s: could not locate my own executable path", argv0);
+
+#ifdef EXEC_BACKEND
+	/* Locate executable backend before we change working directory */
+	if (find_other_exec(argv0, "postgres", PG_BACKEND_VERSIONSTR,
+						postgres_exec_path) < 0)
+		ereport(FATAL,
+				(errmsg("%s: could not locate matching postgres executable",
+						argv0)));
+#endif
+
+	/*
+	 * Locate the pkglib directory --- this has to be set early in case we try
+	 * to load any modules from it in response to postgresql.conf entries.
+	 */
+	get_pkglib_path(my_exec_path, pkglib_path);
+
+	/*
+	 * Verify that there's a readable directory there; otherwise the
+	 * Postgres installation is incomplete or corrupt.  (A typical cause
+	 * of this failure is that the postgres executable has been moved or
+	 * hardlinked to some directory that's not a sibling of the installation
+	 * lib/ directory.)
+	 */
+	pdir = AllocateDir(pkglib_path);
+	if (pdir == NULL)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not open directory \"%s\": %m",
+						pkglib_path),
+				 errhint("This may indicate an incomplete PostgreSQL installation, or that the file \"%s\" has been moved away from its proper location.",
+						 my_exec_path)));
+	FreeDir(pdir);
+
+	/*
+	 * XXX is it worth similarly checking the share/ directory?  If the
+	 * lib/ directory is there, then share/ probably is too.
+	 */
+}
+
+
 /*
  * Validate the proposed data directory
  */

src/backend/utils/misc/tzparser.c

@@ -13,7 +13,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/misc/tzparser.c,v 1.7 2009/01/01 17:23:53 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/misc/tzparser.c,v 1.8 2009/05/02 22:02:37 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -326,12 +326,41 @@ ParseTzFile(const char *filename, int depth,
 	tzFile = AllocateFile(file_path, "r");
 	if (!tzFile)
 	{
-		/* at level 0, if file doesn't exist, guc.c's complaint is enough */
+		/*
+		 * Check to see if the problem is not the filename but the directory.
+		 * This is worth troubling over because if the installation share/
+		 * directory is missing or unreadable, this is likely to be the first
+		 * place we notice a problem during postmaster startup.
+		 */
+		int			save_errno = errno;
+		DIR		   *tzdir;
+
+		snprintf(file_path, sizeof(file_path), "%s/timezonesets",
+				 share_path);
+		tzdir = AllocateDir(file_path);
+		if (tzdir == NULL)
+		{
+			ereport(tz_elevel,
+					(errcode_for_file_access(),
+					 errmsg("could not open directory \"%s\": %m",
+							file_path),
+					 errhint("This may indicate an incomplete PostgreSQL installation, or that the file \"%s\" has been moved away from its proper location.",
+							 my_exec_path)));
+			return -1;
+		}
+		FreeDir(tzdir);
+		errno = save_errno;
+
+		/*
+		 * otherwise, if file doesn't exist and it's level 0, guc.c's
+		 * complaint is enough
+		 */
 		if (errno != ENOENT || depth > 0)
 			ereport(tz_elevel,
 					(errcode_for_file_access(),
 					 errmsg("could not read time zone file \"%s\": %m",
 							filename)));
+
 		return -1;
 	}