ntpd: explain why scripts can be run in quick succession

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 14 insertions, 6 deletions

diff --git a/examples/var_service/ntpd/ntp.script b/examples/var_service/ntpd/ntp.script
index 90299ae..76c34bf 100755
--- a/examples/var_service/ntpd/ntp.script
+++ b/examples/var_service/ntpd/ntp.script
@@ -1,10 +1,12 @@
 #!/bin/sh
 
-exec 2>/dev/null
-echo "`tail -n 99 "$0.log"`" >"$0.log"
-
-exec >>"$0.log"
-exec 2>&1
+# Note that there is no provision to prevent several copies of the script
+# to be run in quick succession. In fact, it happens rather often
+# if initial syncronization results in a step.
+# You will see "step" and then "stratum" script runs, sometimes
+# as close as only 0.002 seconds apart.
+#
+# Script should be ready to deal with this.
 
 dt=`date '+%Y-%m-%d %H:%M:%S'`
 
@@ -13,17 +15,23 @@ if test x"$stratum" != x"" \
 && test 4 -ge "$stratum" \
 && test 128 -le "$poll_interval" \
 ; then
+	echo "`tail -n 199 -- "$0.log" 2>/dev/null`" >"$0.log.$$"
 	echo "$dt: $1"\
 		"freq_drift_ppm=$freq_drift_ppm"\
 		"offset=$offset"\
 		"stratum=$stratum"\
 		"poll_interval=$poll_interval,"\
-		"setting hardware clock"
+		"setting hardware clock"\
+		>>"$0.log.$$"
+	mv -- "$0.log.$$" "$0.log"
 	exec hwclock --systohc
 fi
 
+echo "`tail -n 199 -- "$0.log" 2>/dev/null`" >"$0.log.$$"
 echo "$dt: $1"\
 	"freq_drift_ppm=$freq_drift_ppm"\
 	"offset=$offset"\
 	"stratum=$stratum"\
 	"poll_interval=$poll_interval"\
+	>>"$0.log.$$"
+mv -- "$0.log.$$" "$0.log"