/etc/sysctrl.conf
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
net.ipv6.conf.NETWORKINTERFACENAME.disable_ipv6 = 1
sysctl -p
cat /proc/sys/net/ipv6/conf/*/disable_ipv6
/etc/default/grub
GRUB_CMDLINE_LINUX="xxxxx ipv6.disable=1"
update-grub