Guacamole only listening on IPv6 localhost

I have recently installed Apache Guacamole on Ubuntu 20.04 and also tested with the same result on 21.10. I have it all working but have had to do some workarounds because of this issue.

Here is the guide I created after I had completed my install and figured out all the issues.

My question is around whether anyone knows of a way to make guacd listen on both IPv4 and v6? My work around was orginally to disable IPv6 on the server but that needs to be run on each startup. I then discovered I could change the listening address to 127.0.0.1 and it would listen on IPv4 instead of v6. I know this is probably the fix but I don't understand why I can't make guacd listen on both.

Since this is still a high search result for the issue, guacamole 1.4 has moved the config location.

https://guacamole.apache.org/doc/gug/configuring-guacamole.html#configuring-guacd

So adding /etc/guacamole/guacd.conf

[server]

bind_host = 127.0.0.1
bind_port = 4822

Or other bind hosts will get back the ipv4 behaviour.

Since you are not asking for a workaround, but the full background:

1. Check what addresses your bind_host (ie. "localhost") resolves to:

$ python3 -c "import socket
print(set([a[4][0] for a in socket.getaddrinfo('localhost', 4822)]))"

{'127.0.0.1', '::1'}

2. Possibly open a new issue for guacd to properly implement support for dual-stack IPv4/IPv6 and allow specifying a bind_host which has multiple different addresses.

I did some work fixing IPv6-only support in guacd https://issues.apache.org/jira/browse/GUACAMOLE-1190 which was sufficient for my purposes.

Supporting proper IPv6 dual-stack in any TCP server, while also allowing the user to restrict binding to specific addresses means:

• Create multiple sockets
• bind() to all addresses returned by getaddrinfo() (127.0.0.1 and ::1 for "localhost")
• listen() on all successfully bound sockets
• Use select() or poll() to react to incomming clients on all bound sockets at once
• Call accept() to accept a client connection after select() returns without error for a certain socket in the set

For reference see these answers/sites:

Semantics of :: and 0.0.0.0 in dual-stack OSes

How to support both IPv4 and IPv6 connections

select - synchronous I/O multiplexing