$ strace setxkbmap -layout us &> /tmp/setxkbmap

$ grep open /tmp/setxkbmap
open("/etc/ld.so.cache", O_RDONLY)      = 3
open("/usr/lib/libxkbfile.so.1", O_RDONLY) = 3
open("/usr/lib/libX11.so.6", O_RDONLY)  = 3
open("/lib/libc.so.6", O_RDONLY)        = 3
open("/usr/lib/libXau.so.6", O_RDONLY)  = 3
open("/usr/lib/libXdmcp.so.6", O_RDONLY) = 3
open("/lib/libdl.so.2", O_RDONLY)       = 3
open("/home/username/.Xauthority", O_RDONLY) = 4
open("./rules/xfree86-C.lst", O_RDONLY) = -1 ENOENT (No such file or directory)
open("./rules/xfree86.lst", O_RDONLY)   = -1 ENOENT (No such file or directory)
open("/usr/share/X11/xkb/rules/xfree86-C.lst", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/X11/xkb/rules/xfree86.lst", O_RDONLY) = 4
open("/usr/share/X11/xkb/rules/xfree86-C", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/X11/xkb/rules/xfree86", O_RDONLY) = 4