Comment 0 for bug 1669564

root@ubuntu:~# lsb_release -rd
Description: Ubuntu Zesty Zapus (development branch)
Release: 17.04
root@ubuntu:~# apt-cache policy udev
udev:
  Installed: 232-18ubuntu1
  Candidate: 232-18ubuntu1
  Version table:
 *** 232-18ubuntu1 500
        500 http://archive.ubuntu.com/ubuntu zesty/main amd64 Packages
        100 /var/lib/dpkg/status

3. udevadm trigger --verbose --subsystem-match=net --action=add will run
read .link files from /run/systemd/network/10-netplan-interface1.link
and apply MTU settings

4. during boot running (3) does not set the MTU; running (3) after boot has complete does.

Here'a log during boot where cloud-init generates a netplan config,
invokes netplan-generate and then udevadm trigger. Upon logging in
interface1 has an MTU of 1500. Re-running udevadm trigger now
runs the rules/link files and updates the MTU.

Note that, if you run udevadm test /sys/class/net/interface1; this also will
apply the MTU (test probably shouldn't change the interface, I'll file a
bug for that as well).

# journalctl -o short-precise --no-pager -b | grep WARK
Mar 02 19:17:19.839797 ubuntu cloud-init[647]: WARK: ['netplan', '--debug', 'generate']:
Mar 02 19:17:19.839797 ubuntu cloud-init[647]: WARK: ['stat', '/run/systemd/network/10-netplan-interface1.link']:
Mar 02 19:17:19.839797 ubuntu cloud-init[647]: WARK: ['cat', '/run/systemd/network/10-netplan-interface1.link']:
Mar 02 19:17:19.839797 ubuntu cloud-init[647]: WARK: ['systemctl', 'start', '--no-block', 'systemd-udev-trigger.service']:
Mar 02 19:17:19.839797 ubuntu cloud-init[647]: WARK: ['udevadm', 'trigger', '--verbose', '--subsystem-match=net', '--action=add']:

root@ubuntu:~# cat /run/systemd/network/10-netplan-interface1.link
[Match]
MACAddress=52:54:00:12:34:02

[Link]
Name=interface1
WakeOnLan=off
MTUBytes=1492

root@ubuntu:~# ifconfig interface1
interface1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
        inet 10.0.2.100 netmask 255.255.255.0 broadcast 10.0.2.255
        inet6 fe80::5054:ff:fe12:3402 prefixlen 64 scopeid 0x20<link>
        inet6 fec0::5054:ff:fe12:3402 prefixlen 64 scopeid 0x40<site>
        ether 52:54:00:12:34:02 txqueuelen 1000 (Ethernet)
        RX packets 16 bytes 5053 (5.0 KB)
        RX errors 0 dropped 0 overruns 0 frame 0
        TX packets 35 bytes 3287 (3.2 KB)
        TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

root@ubuntu:~# udevadm trigger --verbose --subsystem-match=net --action=add
/sys/devices/pci0000:00/0000:00:04.0/virtio1/net/interface1
/sys/devices/pci0000:00/0000:00:05.0/virtio2/net/interface2
  ys/devices/pci0000:00/0000:00:06.0/virtio3/net/interface0
/sys/devices/virtual/net/lo

root@ubuntu:~# ifconfig interface1
interface1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1492
        inet 10.0.2.100 netmask 255.255.255.0 broadcast 10.0.2.255
        inet6 fe80::5054:ff:fe12:3402 prefixlen 64 scopeid 0x20<link>
        inet6 fec0::5054:ff:fe12:3402 prefixlen 64 scopeid 0x40<site>
        ether 52:54:00:12:34:02 txqueuelen 1000 (Ethernet)
        RX packets 16 bytes 5053 (5.0 KB)
        RX errors 0 dropped 0 overruns 0 frame 0
        TX packets 37 bytes 3504 (3.5 KB)
        TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

ProblemType: Bug
DistroRelease: Ubuntu 17.04
Package: udev 232-18ubuntu1
ProcVersionSignature: Ubuntu 4.10.0-8.10-generic 4.10.0-rc8
Uname: Linux 4.10.0-8-generic x86_64
ApportVersion: 2.20.4-0ubuntu2
Architecture: amd64
Date: Thu Mar 2 19:22:14 2017
Lsusb: Error: command ['lsusb'] failed with exit code 1:
MachineType: QEMU Standard PC (i440FX + PIIX, 1996)
ProcEnviron:
 TERM=vt220
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.10.0-8-generic root=UUID=8bbb84fe-91e8-4a9a-bd91-f6af4793727e ro console=ttyS0
SourcePackage: systemd
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 04/01/2014
dmi.bios.vendor: SeaBIOS
dmi.bios.version: 1.10.1-1ubuntu1
dmi.chassis.type: 1
dmi.chassis.vendor: QEMU
dmi.chassis.version: pc-i440fx-zesty
dmi.modalias: dmi:bvnSeaBIOS:bvr1.10.1-1ubuntu1:bd04/01/2014:svnQEMU:pnStandardPC(i440FX+PIIX,1996):pvrpc-i440fx-zesty:cvnQEMU:ct1:cvrpc-i440fx-zesty:
dmi.product.name: Standard PC (i440FX + PIIX, 1996)
dmi.product.version: pc-i440fx-zesty
dmi.sys.vendor: QEMU