Hi @QuarkQuartet ,
and welcome to the ROOT forum!
There is a known problem with xrootd in v6.26.02, you can see this popped up a few times on the forum. Can you please try emptying the build directory and build instead the v6-26-00-patches branch?
Also note that unless you have very specific needs you don’t have to build ROOT from source, see Installing ROOT - ROOT.
Cheers,
Enrico