/lib/dhcpcd/dhcpcd-hooks/29-lookup-hostname is in dhcpcd5 5.2.12-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 | # Lookup the hostname in DNS if not set
lookup_hostname()
{
[ -z "$new_ip_address" ] && return 1
local h=
# Silly ISC programs love to send error text to stdout
if type dig >/dev/null 2>&1; then
h=$(dig +short -x $new_ip_address)
if [ $? = 0 ]; then
echo "$h" | sed 's/\.$//'
return 0
fi
elif type host >/dev/null 2>&1; then
h=$(host $new_ip_address)
if [ $? = 0 ]; then
echo "$h" \
| sed 's/.* domain name pointer \(.*\)./\1/'
return 0
fi
fi
return 1
}
set_hostname()
{
if [ -z "$new_host_name" -a -z "$new_fqdn_name" ]; then
export new_host_name="$(lookup_hostname)"
fi
}
if $if_up; then
set_hostname
fi
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