when I try to start xdm/GNU Linux 2.6.x as guest in VirtualBox (host win10) I get this:

XDMCP: socket creation failed, errno 97 (ha, errno, the bane of C, is error what on which OS?)
XDMCP: socket multicast join to 0.0.0.0 failed, error 22

in virtualbox Host Network Manager i set the IP manually to my linux LAN ip (which does not match the win10's automatic DHCP). none the less I can ping or sshd to both localhost and hostname. if i boot the PC using the same kernel (sans VM options, same networking options) everything works fine.

QUESTION: i'm not so familiar with networking I know where to start to trace this issue down. i see nothing unusual or different about ifconfig(1) setup or route(1) setup. what are the software / hardware requirements for multicast to 0.0.0.0 to open the socket ??

finally i tried: X -query 127.0.0.1, and it worked

apparently virtual box networking has done something "strange". perhaps fixable at some time (time i may not have). i cannot see the issue yet as what else seems to work; but suspect the ethernet driver is doing something strange, or resolv.conf needs to be created with something "unusual" (which it didn't need before).

the video speed (VESA) is terrible, slower than S3 on an i386 if I have to guess (that's 1980's speed except with slighter bigger desktop possible). but even that is broken: my win10 desktop limits the X11 desktop size! the mouse cursor is broken until i hack X11 to be small enough to fit inside win10 border without issues: i can only move mouse in bottom half or bottom 3/4 depending on virtual size, so far.

very very disappointing: big mfg dropped support for anything that works with X11 (ie vesa) unless you add hardware (ie, i now have 3 video cards, only the 1990's card works). they made claims "you can go virtual", but even on a fast PC with nvidia drivers under win10: it's all a lie