[Buildroot] [PATCH v5] package/ntp: sntp time sync script

Matt Weber matthew.weber at rockwellcollins.com
Wed Dec 12 03:45:37 UTC 2018

This patch adds the installation of a startup script if the sntp
utility is selected as an option. The utility is design to do a
one time step/slew adjustment of the system time (similar to the
ntpdate tool http://support.ntp.org/bin/view/Dev/DeprecatingNtpdate).
One nice benefit over ntpdate is that sntp can run while ntpd is still
running. However, ntpd may still need to be restarted if the time
step was large enough.

The script provides the ability to override the arguments as part of a
/etc/defaults/sntp file.

On a local LAN, the initial large step adjustment took less then
one second to be retrieved and system time updated. If a user already
has a RTC maintaining the time and the system was powered off for
a long period of time, the script assumes a slew adjustment when
+/- 128ms, rather then a time step(jump). This could be further
tuned by a user with the /etc/defaults/sntp configuration file.

One NTP pool server is being set as sntp uses all of the servers
provided when the DNS is resolved as servers to attempt to retrieve
time from before timing out. It looks like currently that is 4 servers
per *pool.ntp.org hostname.

Cc: Oscar Gomez Fuente <oscargomezf at gmail.com>
Signed-off-by: Matthew Weber <matthew.weber at rockwellcollins.com>
v4 -> v5
 - Fixed permissions on S48sntp and S49ntp scripts

 - Updated script to follow Carlos's recently merged syslog script
 - Added kconfig help comment about the script
 - Added notes in S49sntp about behavior of the tool
 - shellcheck fixes
 - Moved touch of key database file into start function

v3 -> v4
 - Updated S48sntp script to just use a single pool host which provides
   4 NTP servers sntp will query before timing out

v2 -> v3
 - Moved initial time set to a S48sntp script as originally suggested
   by Oscar and preferred by Arnout
 - Switched to sntp tool as it simplified the logic around when and
   how do we call the tool to perform this time sync (it handles
   when to slew/step and multiple servers at once)

v1 -> v2
 - Moved NTP_WAIT_DELAY above sourcing of configuration file
 - Switched to using unix time for current time check
 - Added comment on why redirection of stdout and stderr
 - Attempted to use the pid file but found it added more calls
   to the shell then using a variable, so switched back
 - Adjusted printout so the actual ntpd service start was aligned
   with the respecting Ok/Fail.
 - Dropped -g from the main service call as the "big" time jump
   should have already occurred with the one-shot ntpd -gq.

Based on Oscar's v1 patch to add a ntpdate startup script.
 package/ntp/Config.in |  7 ++++++-
 package/ntp/S48sntp   | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++
 package/ntp/S49ntp    |  0
 package/ntp/ntp.mk    |  9 +++++++++
 4 files changed, 70 insertions(+), 1 deletion(-)
 create mode 100644 package/ntp/S48sntp
 mode change 100755 => 100644 package/ntp/S49ntp

diff --git a/package/ntp/Config.in b/package/ntp/Config.in
index efd47e1..97d933b 100644
--- a/package/ntp/Config.in
+++ b/package/ntp/Config.in
@@ -12,7 +12,12 @@ if BR2_PACKAGE_NTP
 	bool "sntp"
-	  Simple network time protocol program
+	  Simple network time protocol program (a replacement
+	  for the ntpdate tool)
+	  A script is installed as S48sntp which will retrieve and
+	  step the time if there is a large difference before ntpd
+	  takes over the necessary slew adjustments in S49ntp.
 	bool "ntp-keygen"
diff --git a/package/ntp/S48sntp b/package/ntp/S48sntp
new file mode 100644
index 0000000..96d8d50
--- /dev/null
+++ b/package/ntp/S48sntp
@@ -0,0 +1,55 @@
+# sntp uses all the IPs resolved for the hostname (i.e. pool.ntp.org has 4).
+# It will try each until they either all timeout or time has been set. Thus
+# default to only providing one NTP pool host.
+# Step if time delta is greater then 128ms, otherwise slew
+SNTP_ARGS="-Ss -M 128"
+# shellcheck source=/dev/null
+[ -r "/etc/default/$DAEMON" ] && . "/etc/default/$DAEMON"
+start() {
+	printf 'Starting %s: ' "$DAEMON"
+	# Create key cache file to prevents warning that file is missing
+	# shellcheck disable=SC2086 # we need the word splitting
+	# sntp behavior
+	# - Does not background
+	# - Does not infinitely block
+	# - Time-out w/o network = ~2 sec
+	# - Time-out w/ network = ~5sec * # of servers
+	status=$?
+	if [ "$status" -eq 0 ]; then
+		echo "OK"
+	else
+		echo "FAIL"
+	fi
+	return "$status"
+stop() {
+	echo "Nothing to do, $DAEMON is not a daemon."
+restart() {
+	stop
+	sleep 1
+	start
+reload() {
+	echo "Nothing to do, $DAEMON does not support reload."
+case "$1" in
+	start|stop|restart|reload)
+		"$1";;
+	*)
+		echo "Usage: $0 {start|stop|restart|reload}"
+		exit 1
diff --git a/package/ntp/S49ntp b/package/ntp/S49ntp
old mode 100755
new mode 100644
diff --git a/package/ntp/ntp.mk b/package/ntp/ntp.mk
index af3c1aa..aad1cdd 100644
--- a/package/ntp/ntp.mk
+++ b/package/ntp/ntp.mk
@@ -93,9 +93,18 @@ define NTP_INSTALL_TARGET_CMDS
 	$(INSTALL) -m 644 package/ntp/ntpd.etc.conf $(TARGET_DIR)/etc/ntp.conf
+# This script will step the time if there is a large difference
+# before ntpd takes over the necessary slew adjustments
+ifeq ($(BR2_PACKAGE_NTP_SNTP),y)
+	$(INSTALL) -D -m 755 package/ntp/S48sntp $(TARGET_DIR)/etc/init.d/S48sntp
 ifeq ($(BR2_PACKAGE_NTP_NTPD),y)
 	$(INSTALL) -D -m 755 package/ntp/S49ntp $(TARGET_DIR)/etc/init.d/S49ntp

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