mac@shrooms:~$ grep disable /etc/sysctl.conf 
#  Enabling this option disables Stateless Address Autoconfiguration
# settings are disabled so review and enable them as needed.
#net/ipv6/conf/eth0/disable_ipv6
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.eth0.disable_ipv6 = 1
net.ipv6.conf.wlan0.disable_ipv6 = 1
#net.ipv6.conf.virbr0.disable_ipv6 = 1
#net.ipv6.conf.br0.disable_ipv6 = 1