The more formal way of doing this, which fits in with the don’t-change-a-core-system-file-otherwise-it-could-be-replaced-when-you-upgrade-packages-and-your-changes-could-be-lost methodology, and such that it continues across a reboot, is as follows:
# create the long-life config file
echo "net.ipv6.conf.all.disable_ipv6 = 1 net.ipv6.conf.default.disable_ipv6 = 1 net.ipv6.conf.lo.disable_ipv6 = 1" | sudo tee /etc/sysctl.d/99-my-disable-ipv6.conf
# ask the system to use it
sudo service procps reload
# check the result
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