22 lines
1.0 KiB
Bash
22 lines
1.0 KiB
Bash
#!/bin/bash
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# Fallback for the clock. If chrony has no time server after two minutes of
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# uptime (for instance when the campus network blocks NTP), the clock is set
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# from the Date header of the contest site, which is accurate to the second.
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CONF=/etc/contest-firewall
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[ "$(cut -d. -f1 /proc/uptime)" -ge 120 ] || exit 0
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if chronyc -n sources 2>/dev/null | grep -qE '^\^\*'; then
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exit 0
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fi
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site=$(sed -e 's/#.*//' -e 's/[[:space:]]//g' "$CONF/allowed_domains.txt" | grep -m1 .)
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# -k: certificates cannot be checked while the clock is far off
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date_header=$(curl -skI --max-time 10 "https://$site/" | tr -d '\r' | sed -n 's/^[Dd]ate: //p')
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[ -n "$date_header" ] || { logger -t time_from_contest "no answer from $site"; exit 1; }
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server=$(date -d "$date_header" +%s) || exit 1
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now=$(date +%s)
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offset=$((server - now))
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if [ "${offset#-}" -ge 2 ]; then
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# The header has whole seconds: aim for the middle of the second
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date -s "@$server.5" >/dev/null
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logger -t time_from_contest "chrony has no time server; clock set from $site (was off by $offset s)"
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fi
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