On my machine (Linux 3.6.34 x86_64) ifconfig -a returns only the loopback interface instead of the list of all the interfaces installed on the machine.
I tried to reproduce the problem, but failed. Can you reproduce the problem if you don't pass the --all option to ifconfig (should hopefully be the same behaviour)? Could you run ifconfig in gdb, and put a breakpoint on printf, and then do and `p fflush(stdin)' between each call? If that that works, then it is a buffer problem.
