I have the same problem; syslog doesn't tell much, but kern.log tells a bit more - "something" is restarting NetworkManager, and the restart results in losing network connection(s); see below; I have standard ubuntu 16.04 LTS 64bit kept up-to-date as a VM within VirtualBox with Win7/64 host and the latest Vbox version (this had been happening across several Vbox updates; but on the same Vbox version, it wasn't happening on ubuntu 14.10 VM until I removed that and installed a brand new 16.04 from scratch). I hoped the 16.04 would soon get a patch fixing this but that never happened. I have both the host and the VM running 24/7 and the frequency of losing the network is about this - ignore November/14, that was obviously unusual and not related to the problem. root@ostws0116886lu:~# LC_ALL=C egrep "whoopsi.*offline" /var/log/syslog* /var/log/syslog:Nov 22 15:57:38 ostws0116886lu whoopsie[617]: [15:57:38] offline /var/log/syslog:Nov 23 15:57:58 ostws0116886lu whoopsie[617]: [15:57:58] offline /var/log/syslog:Nov 25 09:21:11 ostws0116886lu whoopsie[617]: [09:21:11] offline /var/log/syslog.1:Nov 15 21:41:08 ostws0116886lu whoopsie[663]: [21:41:08] offline /var/log/syslog.1:Nov 16 22:02:29 ostws0116886lu whoopsie[663]: [22:02:29] offline root@ostws0116886lu:~# LC_ALL=C xzegrep "whoopsi.*offline" /var/log/syslog*.xz /var/log/syslog.2.xz:Nov 6 09:47:04 ostws0116886lu whoopsie[26233]: [09:47:04] offline /var/log/syslog.2.xz:Nov 9 08:03:06 ostws0116886lu whoopsie[637]: [08:03:06] offline /var/log/syslog.2.xz:Nov 9 08:04:43 ostws0116886lu whoopsie[640]: [08:04:43] offline /var/log/syslog.2.xz:Nov 10 15:57:30 ostws0116886lu whoopsie[685]: [15:57:30] offline /var/log/syslog.2.xz:Nov 14 10:02:59 ostws0116886lu whoopsie[641]: [10:02:59] offline /var/log/syslog.2.xz:Nov 14 10:03:31 ostws0116886lu whoopsie[626]: [10:03:31] offline /var/log/syslog.2.xz:Nov 14 10:25:23 ostws0116886lu whoopsie[721]: [10:25:23] offline /var/log/syslog.2.xz:Nov 14 10:26:02 ostws0116886lu whoopsie[618]: [10:26:02] offline /var/log/syslog.2.xz:Nov 14 10:26:25 ostws0116886lu whoopsie[656]: [10:26:25] offline /var/log/syslog.2.xz:Nov 14 10:46:50 ostws0116886lu whoopsie[663]: [10:46:50] offline /var/log/syslog.3.xz:Nov 2 11:53:15 ostws0116886lu whoopsie[666]: [11:53:15] offline /var/log/syslog.3.xz:Nov 3 11:53:26 ostws0116886lu whoopsie[666]: [11:53:26] offline /var/log/syslog.3.xz:Nov 4 12:02:52 ostws0116886lu whoopsie[666]: [12:02:52] offline /var/log/syslog.4.xz:Oct 25 02:02:43 ostws0116886lu whoopsie[693]: [02:02:43] offline /var/log/syslog.4.xz:Oct 27 15:45:18 ostws0116886lu whoopsie[693]: [15:45:18] offline /var/log/syslog.4.xz:Oct 28 10:21:56 ostws0116886lu whoopsie[647]: [10:21:56] offline /var/log/syslog.4.xz:Oct 29 10:22:09 ostws0116886lu whoopsie[647]: [10:22:09] offline kern.log: --- Nov 24 09:20:58 ostws0116886lu NetworkManager[632]: [1479979258.9094] caught SIGTERM, shutting down normally. Nov 24 09:20:58 ostws0116886lu NetworkManager[632]: [1479979258.9662] exiting (success) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.2438] NetworkManager (version 1.2.2) is starting... Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.2483] Read config: /etc/NetworkManager/NetworkManager.conf (etc: default-wifi-powersave-on.conf) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.2532] manager[0x24e21a0]: monitoring kernel firmware directory '/lib/firmware'. Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.2536] monitoring ifupdown state file '/run/network/ifstate'. Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.2603] dns-mgr[0x24f28b0]: set resolv-conf-mode: dnsmasq, plugin="dnsmasq" Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.2607] dns-mgr[0x24f28b0]: using resolv.conf manager 'resolvconf' Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3473] init! Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3521] management mode: unmanaged Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3523] devices added (path: /sys/devices/pci0000:00/0000:00:03.0/virtio0/net/enp0s3, iface: enp0s3) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3524] device added (path: /sys/devices/pci0000:00/0000:00:03.0/virtio0/net/enp0s3, iface: enp0s3): no ifupdown configuration found. Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3524] devices added (path: /sys/devices/virtual/net/lo, iface: lo) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3525] device added (path: /sys/devices/virtual/net/lo, iface: lo): no ifupdown configuration found. Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3525] end _init. Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3525] settings: loaded plugin ifupdown: (C) 2008 Canonical Ltd. To report bugs please use the NetworkManager mailing list. (/usr/lib/x86_64-linux-gnu/NetworkManager/libnm-settings-plugin-ifupdown.s o) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3526] settings: loaded plugin keyfile: (c) 2007 - 2015 Red Hat, Inc. To report bugs please use the NetworkManager mailing list. Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3530] SettingsPlugin-Ofono: init! Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3530] SettingsPlugin-Ofono: file doesn't exist: /var/lib/ofono Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3531] SettingsPlugin-Ofono: end _init. Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3531] settings: loaded plugin ofono: (C) 2013-2016 Canonical Ltd. To report bugs please use the NetworkManager mailing list. (/usr/lib/x86_64-linux-gnu/NetworkManager/libnm-settings-plugin-ofono.so ) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3531] (38818864) ... get_connections. Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3531] (38818864) ... get_connections (managed=false): return empty list. Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3559] SettingsPlugin-Ofono: (38819024) ... get_connections. Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3561] SettingsPlugin-Ofono: (38819024) connections count: 0 Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.3561] get unmanaged devices count: 0 Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4836] settings: hostname: using hostnamed Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4836] settings: hostname changed from (none) to "ostws0116886lu" Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4839] Using DHCP client 'dhclient' Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4839] manager: WiFi enabled by radio killswitch; enabled by state file Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4840] manager: WWAN enabled by radio killswitch; enabled by state file Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4840] manager: Networking is enabled by state file Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4840] Loaded device plugin: NMVxlanFactory (internal) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4841] Loaded device plugin: NMVlanFactory (internal) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4841] Loaded device plugin: NMVethFactory (internal) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4841] Loaded device plugin: NMTunFactory (internal) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4841] Loaded device plugin: NMMacvlanFactory (internal) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4841] Loaded device plugin: NMIPTunnelFactory (internal) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4842] Loaded device plugin: NMInfinibandFactory (internal) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4842] Loaded device plugin: NMEthernetFactory (internal) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4842] Loaded device plugin: NMBridgeFactory (internal) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4842] Loaded device plugin: NMBondFactory (internal) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4950] Loaded device plugin: NMWwanFactory (/usr/lib/x86_64-linux-gnu/NetworkManager/libnm-device-plugin-wwan.so) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.4990] Loaded device plugin: NMAtmManager (/usr/lib/x86_64-linux-gnu/NetworkManager/libnm-device-plugin-adsl.so) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5034] Loaded device plugin: NMWifiFactory (/usr/lib/x86_64-linux-gnu/NetworkManager/libnm-device-plugin-wifi.so) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5099] Loaded device plugin: NMBluezManager (/usr/lib/x86_64-linux-gnu/NetworkManager/libnm-device-plugin-bluetooth.so) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5109] device (enp0s3): link connected Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5120] manager: (enp0s3): new Ethernet device (/org/freedesktop/NetworkManager/Devices/0) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5143] keyfile: add connection in-memory (c4843ab8-a696-32e4-aace-39a02d637d6f,"Wired connection 1") Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5210] settings: (enp0s3): created default wired connection 'Wired connection 1' Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5226] device (enp0s3): state change: unmanaged -> unavailable (reason 'managed') [10 20 2] Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: nm_device_get_device_type: assertion 'NM_IS_DEVICE (self)' failed Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5264] device (lo): link connected Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5273] manager: (lo): new Generic device (/org/freedesktop/NetworkManager/Devices/1) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5430] urfkill disappeared from the bus Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5611] device (enp0s3): state change: unavailable -> disconnected (reason 'none') [20 30 0] Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5624] policy: auto-activating connection 'Wired connection 1' Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5661] device (enp0s3): Activation: starting connection 'Wired connection 1' (c4843ab8-a696-32e4-aace-39a02d637d6f) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5664] device (enp0s3): state change: disconnected -> prepare (reason 'none') [30 40 0] Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5667] manager: NetworkManager state is now CONNECTING Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5673] device (enp0s3): state change: prepare -> config (reason 'none') [40 50 0] Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5686] device (enp0s3): state change: config -> ip-config (reason 'none') [50 70 0] Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.5726] dhcp4 (enp0s3): activation: beginning transaction (timeout in 45 seconds) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.6192] dhcp4 (enp0s3): dhclient started with pid 3489 Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.6221] ofono is now available Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.6234] failed to enumerate oFono devices: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.ofono was not provided by any .service files Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.6976] ModemManager available in the bus Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7212] address 10.0.2.15 Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7213] plen 24 (255.255.255.0) Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7213] gateway 10.0.2.2 Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7213] server identifier 10.0.2.2 Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7213] lease time 86400 Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7213] nameserver '172.20.220.26' Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7213] nameserver '172.20.220.25' Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7214] nameserver '10.5.212.21' Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7214] domain name 'bskyb.com' Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7214] dhcp4 (enp0s3): state changed unknown -> bound Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7225] device (enp0s3): state change: ip-config -> ip-check (reason 'none') [70 80 0] Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7242] device (enp0s3): state change: ip-check -> secondaries (reason 'none') [80 90 0] Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7246] device (enp0s3): state change: secondaries -> activated (reason 'none') [90 100 0] Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7248] manager: NetworkManager state is now CONNECTED_LOCAL Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7486] manager: NetworkManager state is now CONNECTED_GLOBAL Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7492] policy: set 'Wired connection 1' (enp0s3) as default for IPv4 routing and DNS Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7694] dns-plugin[0x24ee840]: starting dnsmasq... Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7735] dns-mgr: Writing DNS information to /sbin/resolvconf Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.7936] device (enp0s3): Activation: successful, device activated. Nov 24 09:20:59 ostws0116886lu NetworkManager[3470]: [1479979259.8012] dnsmasq[0x24ee840]: dnsmasq appeared as :1.73 Nov 24 09:21:04 ostws0116886lu NetworkManager[3470]: [1479979264.6393] manager: startup complete Nov 24 09:21:09 ostws0116886lu NetworkManager[3470]: [1479979269.2874] WiFi hardware radio set enabled Nov 24 09:21:09 ostws0116886lu NetworkManager[3470]: [1479979269.2875] WWAN hardware radio set enabled --- time-correlated syslog entries (no lines skipped within): --- Nov 25 09:17:01 ostws0116886lu CRON[13480]: (root) CMD ( cd / && run-parts --report /etc/cron.hourly) Nov 25 09:21:10 ostws0116886lu avahi-daemon[662]: Withdrawing address record for 10.0.2.15 on enp0s3. Nov 25 09:21:10 ostws0116886lu avahi-daemon[662]: Leaving mDNS multicast group on interface enp0s3.IPv4 with address 10.0.2.15. Nov 25 09:21:10 ostws0116886lu avahi-daemon[662]: Interface enp0s3.IPv4 no longer relevant for mDNS. Nov 25 09:21:11 ostws0116886lu whoopsie[617]: [09:21:11] Cannot reach: https://daisy.ubuntu.com Nov 25 09:21:11 ostws0116886lu whoopsie[617]: [09:21:11] offline