Okay, maybe I'm not quite awake today but how come if I have said file $ ls -lt $PWD/libX11.so.6.2 -rw-r--r-- 1 root root 813680 Dec 15 19:18 /usr/X11R6/lib/libX11.so.6.2 that this fails: $ ifort -O -o cmpfil cmpfil.f -L/usr/X11R6/lib -lX11 ld: cannot find -lX11 Ta, -- Michael Bane Atmospheric Physics Group University of Manchester