thank you for this, now I no longer get the error message upon starting xmonad. However, still nothing gets read by 'tail -f .xmonad-fifo'.
Sorry for the delay on this, things have been "interesting" here of late.
It belatedly occurred to me that this *is* a FIFO, and as such the reader has to open it first, with O_RDWR (or what Haskell calls ReadWriteMode) or it won't get hooked up properly. (This is a POSIXism, and Linux at least is very strict about it; depending on the kernel version, you may see ENXDEV ("No such device or address") or what gets "opened" is a dummy node that will never successfully read or write data.)
Is there some other way to the dynamicLogXinerama information so that I can display it on an applet/appindicator?
dynamicLogXinerama is not very flexible; the documentation notes this, and suggests an alternative which provides most of the same information while giving you flexibility (
dynamicLogXinerama).
All in all, POSIX FIFOs are remarkably useless (and I'm still amazed POSIX found a way to make them even less useful than they were originally) and should probably be avoided.