nm_device_get_device_type: assertion 'NM_IS_DEVICE (self)' failed

The crash report may not be directly linked to the symptom described in the first post.
It says: "Error command: nm-cli... nm object is unknown."

I also get the assertion failure on my Ubuntu 16.10 system, but no crash and network is working fine.
So both problems are different problems and I propose that this bug (according to its title) remains on the assertion failure problem.

The assertion failure is gone in Ubuntu 17.04/zesty.

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

Can confirm this on Ubuntu 16.04

i am having same issue on 16.4. i.e wired connection not connecting when i am booting my machine and if i restart the machine its working file. i was checked the kern.log it shows like

Jun 20 12:24:52 ubuntu NetworkManager[871]: nm_device_get_device_type: assertion 'NM_IS_DEVICE (self)' failed

Thanks
Kanagaraj Dhanapal

I am receiving numerous NM errors on startup, that I captured from /var/log for one boot on Aug 16 18:10: I ask if the preserved ".files in the home/user/ directories could be responsible for these errors?

In the captured "fail" list, NM is the main event per this thread
(nm_device_get_device_type: assertion 'NM_IS_DEVICE (self)' failed)

The problem got more pronounced after:

    sudo add-apt-repository ppa:kubuntu-ppa/backports
    sudo apt update

This was added after plasma repeatedly dropped the window ornaments.

    sudo /var/log# grep fail *log| grep 'Aug 16 18:10'

kern.log:Aug 16 18:10:35 dad314159 kernel: [ 0.173985] acpi PNP0A03:00: _OSC failed (AE_NOT_FOUND); disabling ASPM
kern.log:Aug 16 18:10:35 dad314159 kernel: [ 4.392621] wl: module verification failed: signature and/or required key missing - tainting kernel
kern.log:Aug 16 18:10:36 dad314159 NetworkManager[997]: nm_device_get_device_type: assertion 'NM_IS_DEVICE (self)' failed
kern.log:Aug 16 18:10:36 dad314159 NetworkManager[997]: <warn> [1502921436.6054] failed to enumerate oFono devices: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.ofono was not provided by any .service files
kern.log:Aug 16 18:10:43 dad314159 NetworkManager[997]: <info> [1502921443.7380] device (wlp12s0): state change: need-auth -> failed (reason 'no-secrets') [60 120 7]
kern.log:Aug 16 18:10:43 dad314159 NetworkManager[997]: <warn> [1502921443.7388] device (wlp12s0): Activation: failed for connection 'Disco'
kern.log:Aug 16 18:10:43 dad314159 NetworkManager[997]: <info> [1502921443.7426] device (wlp12s0): state change: failed -> disconnected (reason 'none') [120 30 0]
syslog:Aug 16 18:10:35 dad314159 kernel: [ 0.173985] acpi PNP0A03:00: _OSC failed (AE_NOT_FOUND); disabling ASPM
syslog:Aug 16 18:10:35 dad314159 kernel: [ 4.392621] wl: module verification failed: signature and/or required key missing - tainting kernel
syslog:Aug 16 18:10:35 dad314159 avahi-daemon[988]: chroot.c: open() failed: No such file or directory
syslog:Aug 16 18:10:35 dad314159 thermald[961]: THD engine start failed
syslog:Aug 16 18:10:36 dad314159 NetworkManager[997]: nm_device_get_device_type: assertion 'NM_IS_DEVICE (self)' failed
syslog:Aug 16 18:10:36 dad314159 wpa_supplicant[1334]: dbus: wpa_dbus_get_object_properties: failed to get object properties: (none) none
syslog:Aug 16 18:10:36 dad314159 NetworkManager[997]: <warn> [1502921436.6054] failed to enumerate oFono devices: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.ofono was not provided by any .service files
syslog:Aug 16 18:10:36 dad314159 systemd[1]: networking.service: Unit entered failed state.
syslog:Aug 16 18:10:36 dad314159 systemd[1]: ctdb.service: Unit entered failed state.
syslog:Aug 16 18:10:36 dad314159 colord[1188]: (colord:1188): Cd-WARNING **: failed to get session [pid 1021]: No such device or address
syslog:Aug 16 18:10:39 dad314159 systemd[1]: sddm.service: Unit entered failed state.
syslog:Aug 16 18:10:41 dad314159 colord[1188]: (colord:1188): Cd-WARNING **: failed to get session [pid 1494]: No such device or address
syslog:Aug 16 18:10:42 dad314159 systemd[1]: sddm.service: Unit ente...

Ubuntu 16.04 (xenial) amd64

$ sudo journalctl -b -p err
set 28 22:07:52 system NetworkManager[927]: nm_device_get_device_type: assertion 'NM_IS_DEVICE (self)' failed

$ sudo journalctl -b -p err
-- Logs begin at Sex 2017-09-29 07:50:42 BRT, end at Sex 2017-09-29 07:58:58 BRT. --
Set 29 07:51:03 DTI05 NetworkManager[907]: nm_device_get_device_type: assertion 'NM_IS_DEVICE (self)' failed

Same error. My computer has no wireless card connected. I've tried a lot of things (changed network card for a new one, changed to a different distribution). Maybe is a hardware (motherboard) problem.

Guys...I got this problem solved by running these commands...

Install WICD to manage the network

sudo apt-get install wicd-gtk

Stop and disable Network-Manager

sudo systemctl stop NetworkManager.service
sudo systemctl disable NetworkManager.service

and uninstall avahi-autoipd and isc-dhcp-client using synaptic

But now I'm having two problems, one, system setting is not working 'cause NetworkManager is disabled, two wicd sets a random ip even it's configured as static so when I turn on the system or restart it, I have to disconnect and connect again to wicd recognize the righ ip.

It seems it is a harmless message due to NetworkManager not having connection to any network

Not sure I agree with #13 because message comes AFTER network is up:

Dec 13 05:52:20 alien NetworkManager[902]: <warn> [1513169540.4985] platform-linux: kernel support for IFLA_INET6_ADDR_GEN_MODE failed to detect; assume no support
Dec 13 05:52:20 alien NetworkManager[902]: <info> [1513169540.4991] manager: (enp59s0): new Ethernet device (/org/freedesktop/NetworkManager/Devices/0)
Dec 13 05:52:20 alien NetworkManager[902]: <info> [1513169540.4998] keyfile: add connection in-memory (f1d049d0-ad20-3201-ac70-5cb8cc06a6e5,"Wired connection 1")
Dec 13 05:52:20 alien NetworkManager[902]: <info> [1513169540.5001] settings: (enp59s0): created default wired connection 'Wired connection 1'
Dec 13 05:52:20 alien NetworkManager[902]: <info> [1513169540.5007] device (enp59s0): state change: unmanaged -> unavailable (reason 'managed') [10 20 2]
Dec 13 05:52:20 alien NetworkManager[902]: <info> [1513169540.5025] device (enp59s0): link connected
Dec 13 05:52:20 alien kernel: alx 0000:3b:00.0 enp59s0: NIC Up: 1 Gbps Full
Dec 13 05:52:20 alien NetworkManager[902]: nm_device_get_device_type: assertion 'NM_IS_DEVICE (self)' failed
D

Ubuntu 16.04.3, Kernel 4.14.4, Skylake laptop. IPv6 disabled with kernel command line in grub just because it life seems simpler that way. Only a couple of minor network interruptions requiring reboot over the last month.

My network consists of:
2: enp8s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    inet 10.1.1.1/24 brd 10.1.1.255 scope global enp8s0
3: wlp4s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    inet 192.168.99.2/24 brd 192.168.99.255 scope global wlp4s0
5: ppp0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1484 qdisc pfifo_fast state UNKNOWN group default qlen 3
    inet 220.132.100.42 peer 168.95.98.254/32 scope global ppp0

and it seems all work ok except the service networking status keep showing:
   Active: failed (Result: exit-code) since Sun 2018-03-25 20:47:42 CST; 53min ago
     Docs: man:interfaces(5)
  Process: 953 ExecStart=/sbin/ifup -a --read-environment (code=exited, status=1/FAILURE)
  Process: 859 ExecStartPre=/bin/sh -c [ "$CONFIGURE_INTERFACES" != "no" ] && [ -n "$(ifquery --read-environment --list --exclude=lo)"
 Main PID: 953 (code=exited, status=1/FAILURE)

cant find a fix and lead to also see in service NetworkManager status:
NetworkManager[933]: nm_device_get_device_type: assertion 'NM_IS_DEVICE (self)' failed

but the point is the network function normally, are these two issues related and what's the cause ?

There is a fix for this:
https://ubuntuforums.org/showthread.php?t=2305819

add a file to the /etc/modules-load.d directory to have the modules loaded into the kernel at boot. I just created a file called netfilter.conf and put the following in it:

nf_nat_pptp
nf_conntrack_pptp
nf_conntrack_proto_gre

Is it safe to use this solution? I don't know what those three entries mean.

I created this file with the above mentioned content but it doesn't work for me. I still get error messages:

ntpdate[954]: name server cannot be used: Temporary failure in name resolution (-3)
cze 29 16:34:21 NetworkManager[879]: nm_device_get_device_type: assertion 'NM_IS_DEVICE (self)' failed

On the same machine but on another disk with Manjaro I don't have these errors. I think the problem can be solved by upgrading to the new version of network-manager.

I installed new realtec driver but still no result.

Can you please upgrade network manager in Kubuntu 16.04? It slows down my system start.

I have the same problem on GalliumOS running on an Acer Chromebook R11. I tried the above method (#16) and it did not work.