USB tethering working?

slowcyclist

I'm on daily channel, up-to-date. Testing usb tethering today for the first time, I find it does not work.
In the journal I can see related errors:

usb_moded[1957]: /etc/usb-moded/usb-moded.ini: can't remove stale config file: Read-only file system
usb_moded[1957]: /sys/kernel/config/usb_gadget/g1//functions/rndis.usb0: mkdir failed: No such file or directory
usb_moded[1957]: function rndis.usb0 is not registered
usb_moded[1957]: /sys/kernel/config/usb_gadget/g1//UDC: write failure: Invalid argument
usb_moded[1957]: mode setting failed, try charging_only

Yet, it was reported earlier to be working . Is it a regression? Does it work for you?

Moem

@slowcyclist Have you set your USB setting to USB Tethering?

slowcyclist

@Moem of course, that's what triggers the messages in the journal. In French it's called "partage de connexion USB" and
I've tried both from the system settings and UT tweaks.

Moem

@slowcyclist Okay, just checking
It's always good to check the easy stuff first. Not everyone thinks of the things that you thought of.

gpatel-fr

@slowcyclist

while my experience with USB tethering is non existent on UT, I'd guess that RNDIS support is not compiled in the FP5 kernel.

phablet@ubuntu-phablet:~$ zgrep RNDIS /proc/config.gz
# CONFIG_USB_NET_RNDIS_HOST is not set
# CONFIG_USB_NET_RNDIS_WLAN is not set
# CONFIG_USB_CONFIGFS_RNDIS is not set

a quick test shows that the FP5 is seen as mass storage by the (Linux) computer.

févr. 14 23:19:56 ubuntu-phablet usb_moded[2309]: /sys/kernel/config/usb_gadget/g1//functions/rndis.usb0: mkdir failed: No such file or directory
févr. 14 23:19:56 ubuntu-phablet usb_moded[2309]: function rndis.usb0 is not registered
févr. 14 23:19:56 ubuntu-phablet usb_moded[2309]: /sys/kernel/config/usb_gadget/g1//UDC: write failure: Invalid argument

A quick internet search comes up with a thingy called NCM that the FP5 kernel is supposed to have

phablet@ubuntu-phablet:~$ zgrep NCM /proc/config.gz
CONFIG_USB_NET_CDC_NCM=y
# CONFIG_USB_NET_HUAWEI_CDC_NCM is not set
CONFIG_USB_F_NCM=y
CONFIG_USB_CONFIGFS_NCM=y

however trying to access it generates an error:

phablet@ubuntu-phablet:~$ cat /sys/kernel/config/usb_gadget/g1/functions/ncm.usb0/ifname
cat: /sys/kernel/config/usb_gadget/g1/functions/ncm.usb0/ifname: No such device

there is no rndis.usb0 under /sys/kernel/config/usb_gadget/g1/functions

Note that as far as I can tell, the kernel version has changed with 24.04-1 RC (289 -> 302). Also many things have changed between August 2025 and now.

slowcyclist

@gpatel-fr thanks for digging into this. So, right, it's supposed to use ncm and not rndis, but usb-moded should handle tethering with that .
The file you tried to cat is restricted to root access, but even with sudo, it's not accessible, and that probably explains why the configuration script fails, falling back to charging only.
Maybe the fp5 is missing the corresponding kernel module now, while it had it back in August?
I created a ticket.

FlavioMala

Here's what happened to me (FP5):

USB tethering WORKED until February 22nd (2026), when I installed the candidate release (version 10).

Today I noticed it no longer worked.

I tried switching to the "daily" release channel: I installed "1007" and it still doesn't work.

Then I switched to the stable version ("3") and it still doesn't work.

In the settings, when I log out and log back in, it switches from "tethering" to "charging only"... but sometimes it stays on tethering (but nothing changes).

Even using the UT Tweak Tool, things don't change.

It seems that, installing the new RC, something got corrupted and now it no longer works with any release (but it worked until February 22nd, at least with the previous RC channel, which I was on since the switch to "24 noble").

NB: Connecting a PC, decoder, etc. to the GSM (handy) network via (handy) Wi-Fi/Wlan -> works out of the box... only via USB cable no longer works...