Allow to set server timezone from configuration file [#CLICKHOUSE-2765].

dbms/src/Server/config.xml

@@ -65,6 +65,17 @@
 	<!-- Default database. -->
 	<default_database>default</default_database>
 
+	<!-- Server time zone could be set here.
+
+	     Time zone is used when converting between String and DateTime types,
+		  when printing DateTime in text formats and parsing DateTime from text,
+		  it is used in date and time related functions, if specific time zone was not passed as an argument.
+
+		 Time zone is specified as identifier from IANA time zone database, like UTC or Africa/Abidjan.
+		 If not specified, system time zone at server startup is used.
+	-->
+	<!-- <timezone>Europe/Moscow</timezone> -->
+
 	<!-- Configuration of clusters that could be used in Distributed tables.
 		 https://clickhouse.yandex/reference_en.html#Distributed
 	  -->

libs/libdaemon/src/BaseDaemon.cpp

@@ -745,6 +745,15 @@ void BaseDaemon::initialize(Application& self)
 		}
 	}
 
+	/// This must be done before any usage of DateLUT. In particular, before any logging.
+	if (config().has("timezone"))
+	{
+		if (0 != setenv("TZ", config().getString("timezone").data(), 1))
+			throw Poco::Exception("Cannot setenv TZ variable");
+
+		tzset();
+	}
+
 	std::string log_path = config().getString("logger.log", "");
 	if (!log_path.empty())
 		log_path = Poco::Path(log_path).setFileName("").toString();