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|
#!/bin/sh
USR=$(id -u)
if [ "$USR" != 0 ]; then
echo "Not running as root"
exit 1
fi
DRYRUN=true
BOOTUP=false
while [ "$#" -gt 0 ]; do
case "$1" in
-s)
DRYRUN=false
;;
-b)
BOOTUP=true
esac
done
if $BOOTUP; then
MIN_DIFF=7
MAX_DIFF=86400
else
# Not bootup mode, ntpd present, ntpq yields no error:
# Assume ntpd is up and running, so don't do anything
command -v ntpd > /dev/null && ntpq -p > /dev/null 2>&1 && exit 0
# Same for systemd timesync
systemctl -q is-active systemd-timesyncd && exit 0
# No other timesync, go
MIN_DIFF=4
MAX_DIFF=300
fi
# 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.
$BOOTUP && /usr/local/sbin/slx-wait-online
URLS="
https://www.uni-freiburg.de
https://www.bwlehrpool.de
https://bwlp-masterserver.ruf.uni-freiburg.de
https://www.dfn.de
https://www.switch.ch
https://www.debian.org
https://kernel.org
"
F=$(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 -i ^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 ${DIFF}, 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 ($COUNT) from public servers to adjust time"
ECODE=1
fi
rm -f -- "$F"
exit $ECODE
|
