aredn/files/etc/cron.daily/update-clock

#!/bin/sh
true <<'LICENSE'

  On boot, and every 24 hours, update the clock from the first
  available NTP server we find on the network.

  Part of AREDN® -- Used for creating Amateur Radio Emergency Data Networks
  Copyright (C) 2022 Tim Wilkinson KN6PLV
  See Contributors file for additional contributors

  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 version 3 of the License.

  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 <http://www.gnu.org/licenses/>.

  Additional Terms:

  Additional use restrictions exist on the AREDN® trademark and logo.
    See AREDNLicense.txt for more info.

  Attributions to the AREDN® Project must be retained in the source code.
  If importing this code into a new or existing project attribution
  to the AREDN® project must be added to the source code.

  You must not misrepresent the origin of the material contained within.

  Modified versions must be modified to attribute to the original source
  and be marked in reasonable ways as differentiate it from the original
  version.

LICENSE

exec 2> /dev/null

# If real ntp is running, we don't need to do this
if [ "$(pidof ntpd)" != "" ]; then
    if [ -f /var/state/ntp-stratum ] && [ $(cat /var/state/ntp-stratum) -lt 16 ]; then
        echo -n "ntp" > /tmp/timesync
        exit 0
    fi
fi

for candidate in $(uci -q get system.ntp.server)
do
    if $(ntpd -n -q -p ${candidate}); then
        echo -n "ntp" > /tmp/timesync
        logger -p notice -t update-time "Update clock from ${candidate}"
        exit 0
    fi
done

# NTP servers tend to be poorly advertised, so we have to use a bit of
# heuristics to find them
for candidate in $(grep -i ntp /var/run/services_olsr | sed "s/^.*:\/\/\(.*\):.*$/\1/")
do
    if $(ntpd -n -q -p ${candidate}); then
        echo -n "ntp" > /tmp/timesync
        logger -p notice -t update-time "Update clock from ${candidate}"
        exit 0
    fi
done

rm -f /tmp/timesync

logger -p notice -t update-time "Failed to update clock: No reachable ntpd servers."
exit 1