When you’re looking at a seemingly stuck network process and you realise there’s some kind of IPv6 problem, here’s a command that will shut the IPv6 stack down straight away and hand control back to the IPv4 stack allowing your application to continue:
echo 1 > /proc/sys/net/ipv6/conf/all/disable_ipv6
You can replace all with a particular interface if you like, like eth0
or br0 for example.
To make the change permanent, edit /etc/sysctl.conf and add these lines:
# to disable IPv6 on all interfaces system wide
net.ipv6.conf.all.disable_ipv6 = 1
# to disable IPv6 on a specific interface (e.g., eth0, lo)
net.ipv6.conf.lo.disable_ipv6 = 1
net.ipv6.conf.eth0.disable_ipv6 = 1
EDIT Well I got to a server where this didn’t seem to work, my apps were still listening on IPv6 addresses despite the fact that the system was configured not to use them. Then I found this advice to blacklist the ipv6 module…
$ cat <<EOF >/etc/modprobe.d/blacklist-ipv6.conf
# To turn off IPv6, though you don't need too.
# But anyways.
blacklist ipv6
# eof
EOF