Aaron J. Grier wrote :
| mtree performs chown and chmod operations.  you can't chown if you
| aren't root.

Yes. (I always forget about that chown detail).

But in my case, the chown command works because the directories are
created (by default) with my uid (and I modified the mtree file to put my
user name in the uname variable).

Maybe bsd.pkg.mk should just try to run mtree, see if it works, and then
just print a clear error message? Or is there a reason to do the uid test
before?