Missing "/sys/module/dummy/parameters/" subdir on dummy module

[Thiago Martins]

Hello,

 On Ubuntu 18.04 (fully updated), the following configuration does not work:

 File /etc/modprobe.d/dummy.conf with:

----
 options dummy numdummies=12
----

 File /etc/modules

----
 dummy
----

 The module "dummy" is loaded but, there is no 12 dummies NIC cards!

 The manual workaround is:

---
rmmod dummy
modprobe dummy numdummies=12
---

 I talked on IRC and someone pointed that the dummy module is missing its "/sys/module/dummy/parameters/" subdir, so, I'm filling this bug report now.

Cheers!
---
AlsaVersion: Advanced Linux Sound Architecture Driver Version k4.15.0-22-generic.
AplayDevices: Error: [Errno 2] No such file or directory: 'aplay': 'aplay'
ApportVersion: 2.20.9-0ubuntu7.1
Architecture: amd64
ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord': 'arecord'
AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/by-path', '/dev/snd/hwC0D0', '/dev/snd/pcmC0D0c', '/dev/snd/pcmC0D0p', '/dev/snd/controlC0', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
Card0.Amixer.info: Error: [Errno 2] No such file or directory: 'amixer': 'amixer'
Card0.Amixer.values: Error: [Errno 2] No such file or directory: 'amixer': 'amixer'
DistroRelease: Ubuntu 18.04
IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig': 'iwconfig'
Lsusb:
 Bus 001 Device 002: ID 0627:0001 Adomax Technology Co., Ltd
 Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
 Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
 Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
 Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
MachineType: QEMU Standard PC (i440FX + PIIX, 1996)
Package: linux (not installed)
ProcEnviron:
 TERM=screen
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcFB: 0 qxldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.15.0-22-generic root=UUID=26330e04-49ed-11e8-9cae-525400a53f07 ro
ProcVersionSignature: Ubuntu 4.15.0-22.24-generic 4.15.17
RelatedPackageVersions:
 linux-restricted-modules-4.15.0-22-generic N/A
 linux-backports-modules-4.15.0-22-generic N/A
 linux-firmware 1.173.1
RfKill: Error: [Errno 2] No such file or directory: 'rfkill': 'rfkill'
Tags: bionic uec-images
Uname: Linux 4.15.0-22-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups:

_MarkForUpload: True
dmi.bios.date: 04/01/2014
dmi.bios.vendor: SeaBIOS
dmi.bios.version: 1.10.2-1ubuntu1
dmi.chassis.type: 1
dmi.chassis.vendor: QEMU
dmi.chassis.version: pc-i440fx-bionic
dmi.modalias: dmi:bvnSeaBIOS:bvr1.10.2-1ubuntu1:bd04/01/2014:svnQEMU:pnStandardPC(i440FX+PIIX,1996):pvrpc-i440fx-bionic:cvnQEMU:ct1:cvrpc-i440fx-bionic:
dmi.product.name: Standard PC (i440FX + PIIX, 1996)
dmi.product.version: pc-i440fx-bionic
dmi.sys.vendor: QEMU

[Thiago Martins (martinx)]

I also asked a question about this here:

https://askubuntu.com/questions/1042452/file-etc-modprobe-d-dummy-conf-ignored-on-ubuntu-18-04

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1774731

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Thiago Martins (martinx)]

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[Thiago Martins (martinx)]

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[Thiago Martins (martinx)]

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[Thiago Martins (martinx)]

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[Thiago Martins (martinx)]

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[Thiago Martins (martinx)]

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[Thiago Martins (martinx)]

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[Thiago Martins (martinx)]

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[Thiago Martins (martinx)]

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[Thiago Martins (martinx)]

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[Thiago Martins (martinx)]

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[Thiago Martins (martinx)]

apport information

[Joseph Salisbury (jsalisbury)]

Did this issue start happening after an update/upgrade? Was there a prior kernel version where you were not having this particular problem?

Would it be possible for you to test the latest upstream kernel? Refer to https://wiki.ubuntu.com/KernelMainlineBuilds . Please test the latest v4.17 kernel[0].

If this bug is fixed in the mainline kernel, please add the following tag 'kernel-fixed-upstream'.

If the mainline kernel does not fix this bug, please add the tag: 'kernel-bug-exists-upstream'.

Once testing of the upstream kernel is complete, please mark this bug as "Confirmed".

Thanks in advance.

[0] http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.17

[faleiros (faleiros)]

Using an upstream kernel, bug still there:

# uname -r
4.17.1-041701-generic

# lsb_release -drc
Description: Ubuntu 18.04 LTS
Release: 18.04
Codename: bionic

# cat /etc/modprobe.d/dummy.conf
options dummy numdummies=1

# cat /etc/modules-load.d/dummy.conf
dummy

# lsmod | grep dummy
dummy 16384 0

# ip li sh type dummy
<none-if-found>

# rmmod dummy
# modprobe dummy numdummies=1

# ip li sh type dummy
4: dummy0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether ee:74:c8:7c:32:5a brd ff:ff:ff:ff:ff:ff

So loading manually works! The problem seems to be at boot time.

[dana (okdana)]

Hey there. Just wanted to say that i'm seeing this on Bionic as well, on one
machine with kernel 4.15.0-20-generic and also on a second one with kernel
4.15.0-22-generic. The former obviously hasn't been updated in a little bit. I
didn't notice the problem until just now so i can't say if there was ever a time
when it was working before.

I *can* say that i have several *Xenial* machines running 4.15.0-15-generic and
those don't exhibit the problem. (I don't have `dummy` in my module config on
those, but a boot script runs `modprobe dummy` and that automatically creates
the interface, which i believe is the expected default behaviour.)

On Bionic, it doesn't create the interface unless i manually specify the
`numdummies=<num>` option to `modprobe` (as the other reporters have said) or
unless i have `ip link add` load the module and create it for me (naturally).

I did try adding `dummy` to /etc/modules and `options dummy numdummies=1` to
/etc/modprobe.d/dummy-options.conf. systemd-modules-load says that it inserted
the module, and i can confirm that with `lsmod`, but, again, it doesn't actually
create the interface any more.

I can also confirm that, after the module is loaded, i'm missing
/sys/module/dummy/parameters — whatever that indicates.

[Pedro Serrano (kpiq)]

Same result:

echo "dummy" >> /etc/modules
echo "options dummy numdummies=4" >> /etc/modprobe.d/dummy-options.conf

Reboot...

lsmod|grep dummy ; SHOWS THE dummy MODULE LOADED.
no dummy devices are created.

[Jan-Dirk (jhfbosman)]

Just my two-cents:

I noticed the same bug on both Ubuntu workstation as well as Kubuntu, but my Ubuntu server does not seem to have the same problem. All three are running 18.04 with the 4.15.0.36 kernel.

I tested all three when they were freshly installed (kernel 4.15.0-29-generic) and after upgrade (kernel 5.15.0-29-generic).

I tried three scenarios (none of them used 'numdummies'):

1. Add "dummy" module to /etc/modules
2. Add "dummy" module to /etc/modules-load.d/dummy.conf
3. Add a dummy device with /etc/systemd/network/01-dummy0.netdev

All three scenarios worked on ubuntu server, but none of them on the desktops, even though the dummy module was listed in lsmod.

I wish I had time to troubleshoot more, but I'm just investigating a possible switch from fedora to Ubuntu, and thinks are not looking too good for ubuntu... Five months into their supposed LTS release and several packages I rely on cannot be installed because it does not support 18.04, and now this...

Anyway, just thought I'd mention the working server... Good luck...

[Thiago Martins (martinx)]

Any news about this problem?!

[Thiago Martins (martinx)]

After chatting on IRC, #systemd channel, damjan explained this:

https://github.com/systemd/systemd/blob/master/NEWS#L845

So, actually, the following file:

cat /lib/modprobe.d/systemd.conf

disables "extra" dummies, as follows:

--
options bonding max_bonds=0
options dummy numdummies=0
--

Forcing us to explicitly create the dummy devices per demand (I believe, and I'll try it soon). I guess that it's really time to say goodbye to "ifupdown / /etc/network/interfaces" approach...

Just for testing, after disabling the dummy line out from that file and rebooting it, I have the 12 dummies without my ugly workaround via /etc/rc.local!

See, Jan-Dirk? I thought that I could blame systemd and I got my answer there!

NOTE: I actually like systemd, okay? :-P

It's just a new way of doing this (Netplan? systemd-networkd directly?), Jan, you can safely move to Ubuntu! ^_^

Cheers!