unbound[16451:0] error: can’t bind socket: Cannot assign requested address for ::1

ipv6が無効な環境で、unboundが起動しなかった。
interfaceとdo-ip6というディレクティブを正しく設定することで起動するようになった。

# cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=16.04
DISTRIB_CODENAME=xenial
DISTRIB_DESCRIPTION="Ubuntu 16.04.6 LTS"

# systemctl status unbound
...
Apr 27 01:05:46 hostname unbound[16436]: [1587917146] unbound[16451:0] error: can't bind socket: Cannot assign requested address for ::1
Apr 27 01:05:46 hostname unbound[16436]: [1587917146] unbound[16451:0] fatal error: could not open ports
Apr 27 01:05:46 hostname unbound[16436]:    ...fail!
...

# vi /etc/unbound/unbound.conf.d/ip.conf
server:
        interface: 127.0.0.1
        do-ip4: yes
        do-ip6: no

# systemctl start unbound