Be more verbose when DEBUG RESTART fails.

src/server.c

@@ -1549,16 +1549,29 @@ int restartServer(int flags, mstime_t delay) {
 
     /* Check if we still have accesses to the executable that started this
      * server instance. */
-    if (access(server.executable,X_OK) == -1) return C_ERR;
+    if (access(server.executable,X_OK) == -1) {
+        serverLog(LL_WARNING,"Can't restart: this process has no "
+                             "permissions to execute %s", server.executable);
+        return C_ERR;
+    }
 
     /* Config rewriting. */
     if (flags & RESTART_SERVER_CONFIG_REWRITE &&
         server.configfile &&
-        rewriteConfig(server.configfile) == -1) return C_ERR;
+        rewriteConfig(server.configfile) == -1)
+    {
+        serverLog(LL_WARNING,"Can't restart: configuration rewrite process "
+                             "failed");
+        return C_ERR;
+    }
 
     /* Perform a proper shutdown. */
     if (flags & RESTART_SERVER_GRACEFULLY &&
-        prepareForShutdown(SHUTDOWN_NOFLAGS) != C_OK) return C_ERR;
+        prepareForShutdown(SHUTDOWN_NOFLAGS) != C_OK)
+    {
+        serverLog(LL_WARNING,"Can't restart: error preparing for shutdown");
+        return C_ERR;
+    }
 
     /* Close all file descriptors, with the exception of stdin, stdout, strerr
      * which are useful if we restart a Redis server which is not daemonized. */