I can confirm this issue. I have reproduced the problem and used strace. I've also found the app-armour log entry. The app-armour disallowing the -cf <new location> is presumably intentional. The bug is that dhclient3 does not warn the user or log an error when it's unable to open the file parsed to -cf.
In trace-cust-dhcpclient.log: open("/home/<user>/Scripts/reroute/dhclient-cust-sbsa.conf", O_RDONLY) = -1 EACCES (Permission denied) In kern.log Nov 7 17:09:18 <hostname> kernel: [20777.329386] type=1400 audit(1320678558.977:25): apparmor="DENIED" operation="open" parent=8316 profile="/sbin/dhclient3" name="/home/<user>/Scripts/reroute/dhclient- cust-sbsa.conf" pid=8317 comm="dhclient" requested_mask="r" denied_mask="r" fsuid=0 ouid=1000 The trace was produced as follows: sudo strace -e trace=file dhclient -e IF_METRIC=0 -cf /home/enigma/Scripts/reroute/dhclient-cust-sbsa.conf usb0 &> trace-cust-dhcpclient.log ** Attachment added: "strace log of file IO for dhclient" https://bugs.launchpad.net/ubuntu/+source/dhcp3/+bug/537851/+attachment/2588489/+files/trace-cust-dhcpclient.log -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/537851 Title: dhclient silently ignores unreadable config-file To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/dhcp3/+bug/537851/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs