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