How to disable ipv6 system-wide?

[dasuberadmin]

I’ve followed MrMarkuz about creating a postfix template. When that didn’t work I followed this:

Postfix tries to connect to IPV6 servers and gets "Network unreachable" error

To disable ip6, please try: # check ipv6 ifconfig -a | grep inet6 # make folder for template mkdir -p /etc/e-smith/templates-custom/etc/sysctl.conf # create template-file nano /etc/e-smith/templates-custom/etc/sysctl.conf/99sysctl # content of 99sysctl net.ipv6.conf.all.disable_ipv6 = 1 # expand template expand-template /etc/sysctl.conf # To reflect the changes sysctl -p # check ipv6 again ifconfig -a | grep inet6

After that didn’t work I rebooted the machine and now I cannot access the webUI anymore (ERR_CONNECTION_REFUSED) on port 9090.

Port 80 works fine though, but as soon as I click on Server Manager I get above error.
I’m using the internal IP of the server so its not a DNS issue or something like that.