dhclient tries to send request over non-existent interface, floods syslog

[Alex Yurchenko]

From time to time I'm using a Bluetooth network device (my cellphone). In Linux it shows as bnep0. However when disconnected, this device disappears from ifconfig -a output. Still dclient floods syslog with the following:

Jul 2 22:09:59 void dhclient: DHCPDISCOVER on bnep0 to 255.255.255.255 port 67 interval 8 (xid=0x2c92a43c)
Jul 2 22:09:59 void dhclient: send_packet: No such device or address
Jul 2 22:09:59 void dhclient: dhclient.c:2094: Failed to send 300 byte long packet over bnep0 interface.

That continues even after networking is disabled altogether.

Also, every 15 seconds the following is logged:

Jul 2 22:29:03 void dhclient: PRC: Renewing lease on wlan0.
Jul 2 22:29:03 void dhclient: XMT: Renew on wlan0, interval 10180ms.
Jul 2 22:29:03 void dhclient: RCV: Reply message on wlan0 from fe80::5a23:8cff:fea3:1ec5.
Jul 2 22:29:03 void NetworkManager[948]: <info> (wlan0): DHCPv6 state changed renew6 -> renew6
Jul 2 22:29:03 void NetworkManager[948]: <info> valid_lft 60
Jul 2 22:29:03 void NetworkManager[948]: <info> preferred_lft 30
Jul 2 22:29:03 void NetworkManager[948]: <info> address 2001:14ba:21f8:c00:e8b:fdff:fea1:4a1e
Jul 2 22:29:03 void NetworkManager[948]: <info> nameserver '2001:14b8:1000::1'
Jul 2 22:29:03 void NetworkManager[948]: <info> nameserver '2001:14b8:1000::2'
Jul 2 22:29:03 void NetworkManager[948]: <info> domain search 'bb.dnainternet.fi.'
Jul 2 22:29:03 void dbus[1025]: [system] Activating via systemd: service name='org.freedesktop.nm_dispatcher' unit='dbus-org.freedesktop.nm-dispatcher.service'
Jul 2 22:29:03 void systemd[1]: Starting Network Manager Script Dispatcher Service...
Jul 2 22:29:03 void dbus[1025]: [system] Successfully activated service 'org.freedesktop.nm_dispatcher'
Jul 2 22:29:03 void systemd[1]: Started Network Manager Script Dispatcher Service.

Given that bnep0 interface does not exist, the problem most likely is not in the dhclient itself, but something else that configures it to use non-existent interface.

System information:

# lsb_release -rd
Description: Ubuntu 15.04
Release: 15.04

# uname -a
Linux void 3.19.0-21-generic #21-Ubuntu SMP Sun Jun 14 18:31:11 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

# cat /etc/network/interfaces
# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback

source interfaces.d/*

# ls /etc/network/interfaces.d
virbr0

# cat /etc/network/interfaces.d/virbr0
auto br0
iface br0 inet static
address 10.21.32.1
network 10.21.32.0
netmask 255.255.255.0
broadcast 10.21.32.255
#gateway 10.21.32.1
bridge_ports dummy0
##bridge_fd 9
##bridge_hello 2
##bridge_maxage 12
bridge_max_wait 0
bridge_stp off

# apt-cache policy isc-dhcp-client
isc-dhcp-client:
  Installed: 4.3.1-5ubuntu2.2
  Candidate: 4.3.1-5ubuntu2.2

[Robie Basak (racb)]

Thank you for taking the time to report this bug and helping to make Ubuntu better.

I presume you're using Network Manager to manage the connection to your phone over Bluetooth? Assuming this is so, I think this needs to be looked at from the perspective of Network Manager in the first instance.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[bdped (bdped)]

I also use bluetooth tethering and have my syslog full of messages like this.
I've noticed some
/sbin/dhclient -e IF_METRIC=100 -1 bnep0
processes even without a bluetooth connection. since I don't have a bnep0 interface once the tethering is stopped I just pkill -f bnep0 and my syslog goes silent again.