1 files changed, 77 insertions, 0 deletions
diff --git a/satellit_installer/static_files/timesync/redneck-timesync.sh b/satellit_installer/static_files/timesync/redneck-timesync.sh
new file mode 100755
index 0000000..0175456
--- /dev/null
+++ b/satellit_installer/static_files/timesync/redneck-timesync.sh
@@ -0,0 +1,77 @@
+#!/bin/sh
+
+USR=$(id -u)
+if [ "$USR" != 0 ]; then
+	echo "Not running as root"
+	exit 1
+fi
+
+DRYRUN=false
+[ "x$1" = "x-s" ] || DRYRUN=true
+
+# Check if clock is set properly by probing a bunch of web servers for
+# their current time. Then -- after applying some sanity checks -- pick
+# the median of the results and set the local clock to that time
+# if the difference to our local clock is at least one minute and
+# at most one day (limits adjustable below)
+# This can be pretty useful in constrained environments with no
+# real time servers accessible.
+
+MIN_DIFF=30
+MAX_DIFF=86400
+
+URLS="
+	https://www.google.de
+	https://www.cloudflare.com
+	https://www.uni-freiburg.de
+	https://www.bwlehrpool.de
+	https://www.dfn.de
+	https://www.amazon.de
+	https://www.microsoft.de
+"
+
+F=$(mktemp)
+[ -z "$F" ] && F=/tmp/timesync-boot
+NOW=$(date +%s)
+ECODE=0
+
+# Request all at once, HEAD only, 2 sec timeout
+for url in $URLS; do
+	curl -s -m 2 -I "$url" &
+done | grep ^Date: | cut -c7- | while read -r line || [ -n "$line" ]; do
+	# convert each one to unix timestamp
+	T=$(date -d "$line" +%s)
+	# sanity check
+	[ -n "$T" ] && [ "$T" -gt 1234567890 ] && echo $T
+done | sort -n > "$F"
+
+# Get the median of the sorted values
+COUNT=$(wc -l "$F")
+COUNT=${COUNT%% *}
+if [ "$COUNT" -ge 3 ]; then
+	CENTER=$(( COUNT / 2 + 1 ))
+	BEST=$( head -n "$CENTER" "$F" | tail -n 1 )
+	if [ "$BEST" -gt "$NOW" ]; then
+		DIFF=$(( BEST - NOW ))
+	else
+		DIFF=$(( NOW - BEST ))
+	fi
+	if [ "$DIFF" -gt "$MAX_DIFF" ]; then
+		echo "Clock difference too large ($DIFF seconds); refusing to fix."
+		ECODE=1
+	elif [ "$DIFF" -lt "$MIN_DIFF" ]; then
+		echo "Clock difference ok (within $MIN_DIFF seconds)"
+	elif "$DRYRUN"; then
+		echo "Clock difference is $DIFF, but -s is not passed, not correcting time."
+	else
+		echo "Clock difference is $DIFF seconds, setting..."
+		date -s "@$BEST"
+	fi
+else
+	echo "Not enough time probes from public servers to adjust time"
+	ECODE=1
+fi
+
+rm -f -- "$F"
+exit $ECODE
+