dnswatch

Wait for changes of DNS A/AAAA records and run a given command each time.

install

• make
• sudo make install

usage

dnswatch [@<nameserver>|T<stime>|AAAA] [--] [fqdn] [command] [args]...

The changed records are stored in the envvars $ADDRESSES and $ADDRESS.

"But for what is it good for?!?"

Well, I use it for wireguard clients connecting to a peer with a dynamic address.

dnswatch T30 nonexistent.freemyip.com sh -c 'wg-quick down wg0; wg-quick up wg0'

or

dnswatch @208.67.222.222 T120 AAAA nonexistent.freemyip.com restart_wireguard.sh

more examples

• dnswatch golem.de sh -c 'echo "changed to $ADDRESSES!"' <-- will contact the default name server (1.1.1.1) every 60 seconds, executes the command in case of change
• dnswatch @8.8.8.8 golem.de sh -c 'echo "changed to $ADDRESSES!"' <-- will contact google's name server every 60 seconds, executes the command in case of change
• dnswatch @8.8.8.8 T10 golem.de sh -c 'echo "changed to $ADDRESSES!"' <-- will contact google's name server every 10 seconds, executes the command in case of change
• dnswatch @8.8.8.8 T10 AAAA golem.de sh -c 'echo "changed to $ADDRESSES!"' <-- will contact google's name server every 10 seconds, fetches the AAAA record, executes the command in case of change