Add helper script to update the time from NTP

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>

1 files changed, 67 insertions, 0 deletions

diff --git a/scripts/setntpdate.sh b/scripts/setntpdate.sh
new file mode 100755
index 0000000..c0ed1b4
--- /dev/null
+++ b/scripts/setntpdate.sh
@@ -0,0 +1,67 @@
+#!/bin/sh
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+#
+# Copyright (C) 2018 - David Oberhollenzer
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+#
+
+resolve() {
+	local domain="$1"
+	local server="$2"
+
+	if [ -x "$(command -v dig)" ]; then
+		if [ -z "$server" ]; then
+			dig +short "$domain"
+		else
+			dig +short "@$server" "$domain"
+		fi
+		return $?
+	fi
+
+	if [ -x "$(command -v drill)" ]; then
+		if [ -z "$server" ]; then
+			drill "$domain" | grep "^${domain}." | cut -d$'\t' -f5
+		else
+			drill "@$server" "$domain" | grep "^${domain}." |\
+				cut -d$'\t' -f5
+		fi
+		return $?
+	fi
+	exit 1
+}
+
+try_update() {
+	while read ip; do
+		if ntpdate -bu "$ip"; then
+			return 0
+		fi
+	done
+
+	return 1
+}
+
+pool="pool.ntp.org"
+dns="1.1.1.1"
+
+# try default DNS server first
+resolve "$pool" "" | try_update
+[ $? -eq 0 ] && exit 0
+
+# try fallback public dns server
+ping -q -c 1 "$dns" || exit 1
+
+resolve "$pool" "$dns" | try_update
+exit $?