it appears as if kFreeBSD is not able to set owners of file descriptors. My kernel is 9.0-2-amd64 and libc is 2.13-38, from the Wheezy release.
Many thanks for test case. There is a "typo" in our <bits/fcntl.h> header #if defined __USE_BSD || defined __USE_UNIX98 # define F_SETOWN 5 /* Get owner of socket (receiver of SIGIO). */ # define F_GETOWN 6 /* Set owner of socket (receiver of SIGIO). */ #endif It should be #if defined __USE_BSD || defined __USE_UNIX98 # define F_GETOWN 5 /* Get owner of socket (receiver of SIGIO). */ # define F_SETOWN 6 /* Set owner of socket (receiver of SIGIO). */ #endif Petr