system: require a timezone to be set

Even though no timezone implicitly means UTC, systemd is not all that
happy when it does not have a timezone set. This is all fine on a RW
filesystem because systemd will create a symlink on its own (to
Etc/UTC), but not so much on a RO filesystem, causing all kind of
issues at boot time (up to the point that the system is unusable).

We fix that by requiring that the timezone is actually set. The check is
done by verifying that the timezone file is an actual file; if not set,
the test would find a directory and would thus fail.

Update the help entry accordingly.

Also fix indentation in tzdata.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Richard Braun <rbraun@sceen.net>
Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Cc: Martin Bark <martin@barkynet.com>
Cc: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/tz/tz.mk

@@ -25,15 +25,12 @@ define TZ_INSTALL_TARGET_CMDS
 		$(TARGET_DIR)/usr/share/zoneinfo/iso3166.tab
 	mkdir -p $(TARGET_DIR)/usr/share/zoneinfo/uclibc
 	cp -a $(@D)/output/* $(TARGET_DIR)/usr/share/zoneinfo/uclibc
-	if [ -n "$(TZ_LOCALTIME)" ]; then \
-		if [ ! -f $(TARGET_DIR)/usr/share/zoneinfo/uclibc/$(TZ_LOCALTIME) ]; then \
-			printf "Error: '%s' is not a valid timezone, check your BR2_TARGET_LOCALTIME setting\n" \
-				"$(TZ_LOCALTIME)"; \
-			exit 1; \
-		fi; \
-		cd $(TARGET_DIR)/etc; \
-		ln -sf ../usr/share/zoneinfo/uclibc/$(TZ_LOCALTIME) TZ; \
+	if [ ! -f $(TARGET_DIR)/usr/share/zoneinfo/uclibc/$(TZ_LOCALTIME) ]; then \
+		printf "Error: '%s' is not a valid timezone, check your BR2_TARGET_LOCALTIME setting\n" \
+			"$(TZ_LOCALTIME)"; \
+		exit 1; \
 	fi
+	ln -sf ../usr/share/zoneinfo/uclibc/$(TZ_LOCALTIME) $(TARGET_DIR)/etc/TZ
 endef
 
 $(eval $(generic-package))

package/tzdata/tzdata.mk

@@ -36,16 +36,13 @@ define TZDATA_INSTALL_TARGET_CMDS
 	for zone in posix/*; do \
 	    ln -sfn "$${zone}" "$${zone##*/}"; \
 	done
-	if [ -n "$(TZDATA_LOCALTIME)" ]; then \
-	    if [ ! -f $(TARGET_DIR)/usr/share/zoneinfo/$(TZDATA_LOCALTIME) ]; then \
-	        printf "Error: '%s' is not a valid timezone, check your BR2_TARGET_LOCALTIME setting\n" \
-	               "$(TZDATA_LOCALTIME)"; \
-	        exit 1; \
-	    fi; \
-	    cd $(TARGET_DIR)/etc; \
-	    ln -sf ../usr/share/zoneinfo/$(TZDATA_LOCALTIME) localtime; \
-	    echo "$(TZDATA_LOCALTIME)" >timezone; \
+	if [ ! -f $(TARGET_DIR)/usr/share/zoneinfo/$(TZDATA_LOCALTIME) ]; then \
+		printf "Error: '%s' is not a valid timezone, check your BR2_TARGET_LOCALTIME setting\n" \
+			"$(TZDATA_LOCALTIME)"; \
+		exit 1; \
 	fi
+	ln -sf ../usr/share/zoneinfo/$(TZDATA_LOCALTIME) $(TARGET_DIR)/etc/localtime
+	echo "$(TZDATA_LOCALTIME)" >$(TARGET_DIR)/etc/timezone
 endef
 
 define HOST_TZDATA_BUILD_CMDS

system/Config.in

@@ -448,15 +448,13 @@ config BR2_TARGET_LOCALTIME
 	help
 	  The time zone to install as the default local time, expressed as a
 	  tzdata location, such as:
+	    Etc/UTC             (the default)
 	    GMT
 	    Europe/Paris
 	    America/New_York
 	    Pacific/Wallis
 	    ...
 
-	  If empty, no local time will be set, and the dates will be
-	  expressed in UTC.
-
 endif # BR2_TARGET_TZ_INFO
 
 config BR2_ROOTFS_USERS_TABLES