Re: T420 fan and Ubuntu 25.04

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Good day!

On Sat, Feb 07, 2026 at 02:08:05AM +0100, gregor herrmann wrote:
> On Fri, 06 Feb 2026 19:01:02 +0200, Dennis Yurichev wrote:
> > T420 + Ubuntu 24.04.2 LTS - I could write to /proc/acpi/ibm/fan
> > for fan control.
> > That worked.
> >=20
> > T420 + Ubuntu 25.04 - Now I get:
> >=20
> > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > % cat fan_2.sh
> > echo "level 2" > /proc/acpi/ibm/fan
> >=20
> > % sudo ./fan_2.sh
> > ./fan_2.sh: 1: echo: echo: I/O error
> > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> >=20
> > Known issue (after upgrading)?
>=20
> Do you still have something like
>=20
> # cat /etc/modprobe.d/thinkpad_acpi.conf
> options thinkpad_acpi fan_control=3D1

Yes.

% cat /etc/modprobe.d/thinkpad_acpi.conf
options thinkpad_acpi fan_control=3D1

% sudo grep -i thinkpad /var/log/dmesg
                       BIOS vendor: LENOVO; Ver: 83ET76WW (1.46 ); Product =
Version: ThinkPad
T420
[    5.299925] kernel: thinkpad_acpi: ThinkPad ACPI Extras v0.26
[    5.300072] kernel: thinkpad_acpi: http://ibm-acpi.sf.net/
[    5.300122] kernel: thinkpad_acpi: ThinkPad BIOS 83ET76WW (1.46 ), EC un=
known
[    5.300169] kernel: thinkpad_acpi: Lenovo ThinkPad T420, model 4180AH9
[    5.317030] kernel: thinkpad_acpi: radio switch found; radios are enabled
[    5.317139] kernel: thinkpad_acpi: This ThinkPad has standard ACPI backl=
ight brightness control, supported by the ACPI video driver
[    5.317201] kernel: thinkpad_acpi: Disabling thinkpad-acpi brightness ev=
ents by default...
[    5.354172] kernel: thinkpad_acpi: rfkill switch tpacpi_bluetooth_sw: ra=
dio is unblocked
[    5.355133] kernel: thinkpad_acpi: Standard ACPI backlight interface ava=
ilable, not loading native one
[    5.426089] kernel: thinkpad_acpi: battery 1 registered (start 0, stop 1=
00, behaviours: 0x7)
[    5.439070] kernel: ACPI: battery: new hook: ThinkPad Battery Extension
[    5.466048] kernel: input: ThinkPad Extra Buttons as /devices/platform/t=
hinkpad_acpi/input/input6

--=20
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