The C library function "open" should set errno on failure, as documented in then open(2) man page. This works as expected when open is called from a JNI function running under java 1.4.x or 1.5.x. However, under 1.6.0_01 (also tried 1.6.0_02 and 1.7.0-ea-b12) the errno value is not set. See the simple test program in the CR attachments (don't run the test program as superuser, as it relies on 000 permissions being unreadable).