pg_ctl: improve handling of invalid data directory

Return '4' and report a meaningful error message when a non-existent or
invalid data directory is passed.  Previously, pg_ctl would just report
the server was not running.

Patch by me and Amit Kapila
Report from Peter Eisentraut

doc/src/sgml/ref/pg_ctl-ref.sgml

@@ -208,7 +208,8 @@ PostgreSQL documentation
    the specified data directory. If it is, the <acronym>PID</acronym>
    and the command line options that were used to invoke it are
    displayed.  If the server is not running, the process returns an
-   exit status of 3.
+   exit status of 3.  If an accessible data directory is not specified,
+   the process returns an exit status of 4.
   </para>
 
   <para>

src/bin/pg_ctl/pg_ctl.c

@@ -97,6 +97,7 @@ static bool allow_core_files = false;
 static time_t start_time;
 
 static char postopts_file[MAXPGPATH];
+static char version_file[MAXPGPATH];
 static char pid_file[MAXPGPATH];
 static char backup_file[MAXPGPATH];
 static char recovery_file[MAXPGPATH];
@@ -152,7 +153,7 @@ static void pgwin32_doRunAsService(void);
 static int	CreateRestrictedProcess(char *cmd, PROCESS_INFORMATION *processInfo, bool as_service);
 #endif
 
-static pgpid_t get_pgpid(void);
+static pgpid_t get_pgpid(bool is_status_request);
 static char **readfile(const char *path);
 static void free_readfile(char **optlines);
 static int	start_postmaster(void);
@@ -246,10 +247,34 @@ print_msg(const char *msg)
 }
 
 static pgpid_t
-get_pgpid(void)
+get_pgpid(bool is_status_request)
 {
 	FILE	   *pidf;
 	long		pid;
+	struct stat statbuf;
+
+	if (stat(pg_data, &statbuf) != 0)
+	{
+		if (errno == ENOENT)
+			printf(_("%s: directory \"%s\" does not exist\n"), progname,
+					 pg_data);
+		else
+			printf(_("%s: cannot access directory \"%s\"\n"), progname,
+					 pg_data);
+		/*
+		 * The Linux Standard Base Core Specification 3.1 says this should return
+		 * '4, program or service status is unknown'
+		 * https://refspecs.linuxbase.org/LSB_3.1.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html
+		 */
+		exit(is_status_request ? 4 : 1);
+	}
+
+	if (stat(version_file, &statbuf) != 0 && errno == ENOENT)
+	{
+		printf(_("%s: directory \"%s\" is not a database cluster directory\n"),
+				 progname, pg_data);
+		exit(is_status_request ? 4 : 1);
+	}
 
 	pidf = fopen(pid_file, "r");
 	if (pidf == NULL)
@@ -810,7 +835,7 @@ do_start(void)
 
 	if (ctl_command != RESTART_COMMAND)
 	{
-		old_pid = get_pgpid();
+		old_pid = get_pgpid(false);
 		if (old_pid != 0)
 			write_stderr(_("%s: another server might be running; "
 						   "trying to start server anyway\n"),
@@ -894,7 +919,7 @@ do_stop(void)
 	pgpid_t		pid;
 	struct stat statbuf;
 
-	pid = get_pgpid();
+	pid = get_pgpid(false);
 
 	if (pid == 0)				/* no pid file */
 	{
@@ -943,7 +968,7 @@ do_stop(void)
 
 		for (cnt = 0; cnt < wait_seconds; cnt++)
 		{
-			if ((pid = get_pgpid()) != 0)
+			if ((pid = get_pgpid(false)) != 0)
 			{
 				print_msg(".");
 				pg_usleep(1000000);		/* 1 sec */
@@ -980,7 +1005,7 @@ do_restart(void)
 	pgpid_t		pid;
 	struct stat statbuf;
 
-	pid = get_pgpid();
+	pid = get_pgpid(false);
 
 	if (pid == 0)				/* no pid file */
 	{
@@ -1033,7 +1058,7 @@ do_restart(void)
 
 		for (cnt = 0; cnt < wait_seconds; cnt++)
 		{
-			if ((pid = get_pgpid()) != 0)
+			if ((pid = get_pgpid(false)) != 0)
 			{
 				print_msg(".");
 				pg_usleep(1000000);		/* 1 sec */
@@ -1071,7 +1096,7 @@ do_reload(void)
 {
 	pgpid_t		pid;
 
-	pid = get_pgpid();
+	pid = get_pgpid(false);
 	if (pid == 0)				/* no pid file */
 	{
 		write_stderr(_("%s: PID file \"%s\" does not exist\n"), progname, pid_file);
@@ -1110,7 +1135,7 @@ do_promote(void)
 	pgpid_t		pid;
 	struct stat statbuf;
 
-	pid = get_pgpid();
+	pid = get_pgpid(false);
 
 	if (pid == 0)				/* no pid file */
 	{
@@ -1204,7 +1229,7 @@ do_status(void)
 {
 	pgpid_t		pid;
 
-	pid = get_pgpid();
+	pid = get_pgpid(true);
 	/* Is there a pid file? */
 	if (pid != 0)
 	{
@@ -1247,7 +1272,7 @@ do_status(void)
 
 	/*
 	 * The Linux Standard Base Core Specification 3.1 says this should return
-	 * '3'
+	 * '3, program is not running'
 	 * https://refspecs.linuxbase.org/LSB_3.1.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html
 	 */
 	exit(3);
@@ -2285,6 +2310,7 @@ main(int argc, char **argv)
 	if (pg_data)
 	{
 		snprintf(postopts_file, MAXPGPATH, "%s/postmaster.opts", pg_data);
+		snprintf(version_file, MAXPGPATH, "%s/PG_VERSION", pg_data);
 		snprintf(pid_file, MAXPGPATH, "%s/postmaster.pid", pg_data);
 		snprintf(backup_file, MAXPGPATH, "%s/backup_label", pg_data);
 		snprintf(recovery_file, MAXPGPATH, "%s/recovery.conf", pg_data);