If you are disabling IPv6 then you likely know why you are doing it and the reasons may be varied. Disabling IPv6 only requires a brief search to find the sysctl change required but the Ubuntu bug issue is worth a mention.

Disable IPv6

Modify the following file:

#  vim /etc/sysctl.d/99-sysctl.conf

Add the following lines:

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

Reload values and confirm IPv6 addresses have been removed:

# sysctl -p

Surviving Reboots

There appears to a bug in Ubuntu affecting the sysctl settings loading after reboot.

The fix however is to create a new file /etc/rc.local and add these contents:

# /etc/rc.local

# Load kernel variables from /etc/sysctl.d
/etc/init.d/procps restart

exit 0

You’ll need to ensure the file is executable as well:

chmod 755 /etc/rc.local

Thanks to Bill for his post which likely saved me time searching the interweb for answers…

Disable IPv6 on Ubuntu 18.04
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