I’ve started using Fluxbox a while ago. Primarily in my work computer and next at home.
At my work there’s no problem because I only have one monitor, but at home, I use two monitors and fbsetbg wasn’t doing the trick, even not working sometimes. After a doing research I finally found the answer.
fbsetbg can be used stand alone (finding itself an app to set the background) or you can specify an application for it.
In this case, I’m using feh with xinerama support.
In the fbsetbg manual (man fbsetbg) it says that we need only to specify the background setter once, using the option -u . Still, in my fluxbox startup script I specify the option anyway..
So, to span wallpapers across two monitors, just use feh
fbsetbg -u feh ...picture(s)....
Example in your fluxbox startup file:
fbsetbg -u feh -R <path/to/pictures> &