How do chrooted X clients connect to server?

[Pavel Krc]

Hi all,

I've been using chrooted Debian (and other distros) for years, but there's one thing that baffled me many times. While many users seek help trying to make chrooted X programs work (mostly due to missing DISPLAY=... or xauth problems), I cannot find a reason why this works for me when it clearly shouldn't. I'm running XOrg outside the chroot, which listens only on a socket /tmp/.X11-unix/X0 and no TCP port, as usual. When preparing the chroot, I don't bind /tmp to new root - I mount a new tmpfs, so chrooted /tmp is empty (checked). Therefore, the X clients should have no way of connecting the server, yet they work without any problems. I have studied source codes of Xlib and XCB and found only the expected behavior of trying /tmp/.X11-unix/X{display} and tcp port 6000 + {display} (which is closed). Any ideas how this works or where I should continue my search?

Thanks,

Pavel