The following was in the log once, right after booting with kernel 3.16.0.48 Sep 3 08:25:01 sbh16 kernel: [ 156.921352] ------------[ cut here ]------------ Sep 3 08:25:01 sbh16 kernel: [ 156.921360] WARNING: CPU: 0 PID: 0 at /build/linux-lts-utopic-V0z0lI/linux-lts-utopic-3.16.0/net/sched/sch_generic.c:264 dev_watchdog+0x276/0x280() Sep 3 08:25:01 sbh16 kernel: [ 156.921362] NETDEV WATCHDOG: eth0 (igb): transmit queue 1 timed out Sep 3 08:25:01 sbh16 kernel: [ 156.921363] Modules linked in: ipmi_devintf ipt_REJECT nf_conntrack_ipv4 nf_defrag_ipv4 xt_tcpudp xt_conntrack nf_conntrack intel_rapl x86_pkg_temp_thermal intel_powerclamp coretemp iptable_filter ip_tables x_tables kvm ppdev crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel aes_x86_64 lrw gf128mul glue_helper ablk_helper cryptd joydev lpc_ich winbond_cir rc_core int3403_thermal parport_pc ipmi_si lp parport ipmi_msghandler video mac_hid shpchp uas hid_generic igb usb_storage i2c_algo_bit usbhid dca ahci ptp hid libahci pps_core megaraid_sas Sep 3 08:25:01 sbh16 kernel: [ 156.921391] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.16.0-48-generic #64~14.04.1-Ubuntu Sep 3 08:25:01 sbh16 kernel: [ 156.921394] Hardware name: Intel Corporation S1200RP_SE/S1200RP_SE, BIOS S1200RP.86B.02.01.0002.042120141550 04/21/2014 Sep 3 08:25:01 sbh16 kernel: [ 156.921395] 0000000000000009 ffff88044fc03d98 ffffffff817663e8 ffff88044fc03de0 Sep 3 08:25:01 sbh16 kernel: [ 156.921400] ffff88044fc03dd0 ffffffff8106de3d 0000000000000001 ffff880435b1c000 Sep 3 08:25:01 sbh16 kernel: [ 156.921402] ffff880435bcb940 0000000000000008 0000000000000000 ffff88044fc03e30 Sep 3 08:25:01 sbh16 kernel: [ 156.921406] Call Trace: Sep 3 08:25:01 sbh16 kernel: [ 156.921407] [] dump_stack+0x45/0x56 Sep 3 08:25:01 sbh16 kernel: [ 156.921417] [] warn_slowpath_common+0x7d/0xa0 Sep 3 08:25:01 sbh16 kernel: [ 156.921419] [] warn_slowpath_fmt+0x4c/0x50 Sep 3 08:25:01 sbh16 kernel: [ 156.921421] [] dev_watchdog+0x276/0x280 Sep 3 08:25:01 sbh16 kernel: [ 156.921423] [] ? dev_graft_qdisc+0x80/0x80 Sep 3 08:25:01 sbh16 kernel: [ 156.921429] [] call_timer_fn+0x36/0x100 Sep 3 08:25:01 sbh16 kernel: [ 156.921430] [] ? dev_graft_qdisc+0x80/0x80 Sep 3 08:25:01 sbh16 kernel: [ 156.921434] [] run_timer_softirq+0x20f/0x310 Sep 3 08:25:01 sbh16 kernel: [ 156.921435] [] __do_softirq+0xf5/0x2e0 Sep 3 08:25:01 sbh16 kernel: [ 156.921437] [] irq_exit+0x105/0x110 Sep 3 08:25:01 sbh16 kernel: [ 156.921440] [] smp_apic_timer_interrupt+0x45/0x60 Sep 3 08:25:01 sbh16 kernel: [ 156.921445] [] apic_timer_interrupt+0x6d/0x80 Sep 3 08:25:01 sbh16 kernel: [ 156.921447] [] ? cpuidle_enter_state+0x52/0xc0 Sep 3 08:25:01 sbh16 kernel: [ 156.921453] [] ? cpuidle_enter_state+0x48/0xc0 Sep 3 08:25:01 sbh16 kernel: [ 156.921455] [] cpuidle_enter+0x17/0x20 Sep 3 08:25:01 sbh16 kernel: [ 156.921460] [] cpu_startup_entry+0x31d/0x450 Sep 3 08:25:01 sbh16 kernel: [ 156.921461] [] ? __schedule+0x35f/0x7a0 Sep 3 08:25:01 sbh16 kernel: [ 156.921466] [] rest_init+0x77/0x80 Sep 3 08:25:01 sbh16 kernel: [ 156.921468] [] start_kernel+0x477/0x482 Sep 3 08:25:01 sbh16 kernel: [ 156.921471] [] ? set_init_arg+0x53/0x53 Sep 3 08:25:01 sbh16 kernel: [ 156.921474] [] ? early_idt_handler_array+0x120/0x120 Sep 3 08:25:01 sbh16 kernel: [ 156.921478] [] x86_64_start_reservations+0x2a/0x2c Sep 3 08:25:01 sbh16 kernel: [ 156.921481] [] x86_64_start_kernel+0x143/0x152 Sep 3 08:25:01 sbh16 kernel: [ 156.921482] ---[ end trace 09735e7816a8cf4e ]--- Then 11 messages as follows appear repeatedly every couple of seconds. Sep 3 21:45:00 sbh16 kernel: [48175.942881] igb 0000:03:00.0: Detected Tx Unit Hang Sep 3 21:45:00 sbh16 kernel: [48175.942881] Tx Queue <3> Sep 3 21:45:00 sbh16 kernel: [48175.942881] TDH <4> Sep 3 21:45:00 sbh16 kernel: [48175.942881] TDT <4> Sep 3 21:45:00 sbh16 kernel: [48175.942881] next_to_use <7> Sep 3 21:45:00 sbh16 kernel: [48175.942881] next_to_clean <4> Sep 3 21:45:00 sbh16 kernel: [48175.942881] buffer_info[next_to_clean] Sep 3 21:45:00 sbh16 kernel: [48175.942881] time_stamp <100b68670> Sep 3 21:45:00 sbh16 kernel: [48175.942881] next_to_watch Sep 3 21:45:00 sbh16 kernel: [48175.942881] jiffies <100b68e24> Sep 3 21:45:00 sbh16 kernel: [48175.942881] desc.status <0> And the following two appear after the above set, but not every time - maybe every third time or so. Sep 3 21:45:02 sbh16 kernel: [48177.943489] igb 0000:03:00.0 eth0: Reset adapter Sep 3 21:45:04 sbh16 kernel: [48179.933234] igb 0000:03:00.0 eth0: igb: eth0 NIC Link is Up 100 Mbps Full Duplex, Flow Control: RX/TX Here's lshw root@sbh16:~# lshw -C network *-network description: Ethernet interface product: I210 Gigabit Network Connection vendor: Intel Corporation physical id: 0 bus info: pci@0000:03:00.0 logical name: eth0 version: 03 serial: 00:1e:67:b6:53:b4 size: 100Mbit/s capacity: 1Gbit/s width: 32 bits clock: 33MHz capabilities: pm msi msix pciexpress bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation configuration: autonegotiation=on broadcast=yes driver=igb driverversion=5.2.13-k duplex=full firmware=3.20, 0x800005a2 ip=72.52.113.16 latency=0 link=yes multicast=yes port=twisted pair speed=100Mbit/s resources: irq:17 memory:b1200000-b127ffff ioport:4000(size=32) memory:b1280000-b1283fff *-network description: Ethernet interface product: I210 Gigabit Network Connection vendor: Intel Corporation physical id: 0 bus info: pci@0000:04:00.0 logical name: eth1 version: 03 serial: 00:1e:67:b6:53:b5 size: 100Mbit/s capacity: 1Gbit/s width: 32 bits clock: 33MHz capabilities: pm msi msix pciexpress bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation configuration: autonegotiation=on broadcast=yes driver=igb driverversion=5.2.13-k duplex=full firmware=3.20, 0x800005a5 ip=192.168.2.16 latency=0 link=yes multicast=yes port=twisted pair speed=100Mbit/s resources: irq:18 memory:b1100000-b117ffff ioport:3000(size=32) memory:b1180000-b1183fff And ifconfig root@sbh16:~# ifconfig eth0 Link encap:Ethernet HWaddr 00:1e:67:b6:53:b4 inet addr:72.52.113.16 Bcast:72.52.113.255 Mask:255.255.255.0 inet6 addr: fe80::21e:67ff:feb6:53b4/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:4799466 errors:0 dropped:0 overruns:0 frame:0 TX packets:372113 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:355607936 (355.6 MB) TX bytes:333016763 (333.0 MB) Memory:b1200000-b127ffff eth0:34 Link encap:Ethernet HWaddr 00:1e:67:b6:53:b4 inet addr:72.52.113.34 Bcast:72.52.113.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Memory:b1200000-b127ffff eth0:35 Link encap:Ethernet HWaddr 00:1e:67:b6:53:b4 inet addr:72.52.113.35 Bcast:72.52.113.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Memory:b1200000-b127ffff eth0:36 Link encap:Ethernet HWaddr 00:1e:67:b6:53:b4 inet addr:72.52.113.36 Bcast:72.52.113.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Memory:b1200000-b127ffff eth0:37 Link encap:Ethernet HWaddr 00:1e:67:b6:53:b4 inet addr:72.52.113.37 Bcast:72.52.113.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Memory:b1200000-b127ffff eth0:38 Link encap:Ethernet HWaddr 00:1e:67:b6:53:b4 inet addr:72.52.113.38 Bcast:72.52.113.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Memory:b1200000-b127ffff eth1 Link encap:Ethernet HWaddr 00:1e:67:b6:53:b5 inet addr:192.168.2.16 Bcast:192.168.2.255 Mask:255.255.255.0 inet6 addr: fe80::21e:67ff:feb6:53b5/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:389 errors:0 dropped:0 overruns:0 frame:0 TX packets:8 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:23340 (23.3 KB) TX bytes:648 (648.0 B) Memory:b1100000-b117ffff lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:65536 Metric:1 RX packets:175444 errors:0 dropped:0 overruns:0 frame:0 TX packets:175444 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:36259758 (36.2 MB) TX bytes:36259758 (36.2 MB)