How to set and use the RES_USEVC / usevc option as mentioned in: /usr/src/lib/libc/net/resolver.3 /usr/src/include/resolv.h /usr/src/lib/libc/net/res_debug.c /usr/src/share/man/man5/resolver.5 # options statement / env_var The usevc option does not work when used in place of the debug option below. The debug option works. env - RES_OPTIONS=debug host freebsd.org or resolv.conf: options debug env - host freebsd.org I find usevc in these: /usr/src/include/resolv.h:#define RES_USEVC 0x00000008 /* use virtual circuit */ /usr/src/lib/libc/net/gethostbydns.c: _res.options |RES_STAYOPEN | RES_USEVC; /usr/src/lib/libc/net/gethostbydns.c: _res.options &= ~(RES_STAYOPEN | RES_USEVC); /usr/src/lib/libc/net/getnetbydns.c: _res.options |RES_STAYOPEN | RES_USEVC; /usr/src/lib/libc/net/getnetbydns.c: _res.options &= ~(RES_STAYOPEN | RES_USEVC); /usr/src/lib/libc/net/name6.c: _res.options |= RES_STAYOPEN | RES_USEVC; /usr/src/lib/libc/net/name6.c: _res.options &= ~(RES_STAYOPEN | RES_USEVC); /usr/src/lib/libc/net/res_debug.c: case RES_USEVC: return "usevc"; /usr/src/lib/libc/net/res_send.c: v_circuit = (_res.options & RES_USEVC) || buflen > PACKETSZ; /usr/src/lib/libc/net/res_send.c: if ((v_circuit && (!(_res.options & RES_USEVC) || ns != 0)) || /usr/src/lib/libc/net/resolver.3:.It Dv RES_USEVC /usr/src/lib/libc/net/resolver.3:.Dv RES_USEVC My guess is that it is missing from res_init.c? And that res_init.c may need to be brought fully up to date with whatever the current option set is nowadays? res_init.c:545 /* XXX - print a warning here? */ On an invalid option, yes please, inform userland :) This note refers to RELENG_4. It may also apply to RELENG_7 and HEAD.