[mythtv-users] /dev/dvb permissions

Eyal Lebedinsky eyal at eyal.emu.id.au
Mon Jun 28 05:27:12 UTC 2021

On 28/06/2021 14.16, Stephen Worthington wrote:
> On Mon, 28 Jun 2021 10:50:23 +1000, you wrote:
>> On 21/06/2021 23.49, Eyal Lebedinsky wrote:
>>> After a recent update (fedora 34) mythbackend failed to show any card.
>>> Short story:
>>>   ����crw-rw----+ 1 root rtlsdr 212,� 3 Jun 20 23:10 /dev/dvb/adapter0/frontend0
>>> so user mythtv cannot open it. chmod fixed it, and I added this to my startup scripts.
>>> Was this an intended change? This update brought in
>>>   ����mythtv-backend-31.0-17.147.20210421git05c16580e1.fc34.x86_64
>>> and friends as well as
>>>   ����kernel-5.12.11-300.fc34.x86_64
>>>   ����rtl-sdr-0.6.0-9.fc34.x86_64
>>> The group rtlsdr is new:
>>>   ����Jun 20 22:43:17 e7 groupadd[1678612]: group added to /etc/group: name=rtlsdr, GID=440
>>>   ����Jun 20 22:43:17 e7 groupadd[1678612]: group added to /etc/gshadow: name=rtlsdr
>>>   ����Jun 20 22:43:17 e7 groupadd[1678612]: new group: name=rtlsdr, GID=440
>>> Is there a possible conflict?
>>> Should user mythtv be added to the new group?
>> I still do not know what the correct action should be.
>> 1) I see
>> 	/usr/lib/udev/rules.d/10-rtl-sdr.rules
>> is setting the group rtlsdr to a list of devices which includes my tuners 0bda:2838
>> Is this proper to do so when there are other users of these devices?
>> 2) If root.rtlsdr is correct, should the user 'mythtv' also be a member of 'rtlsdr'?
>>     How should this be done without every mythtv user doing it manually once the backend fails?
>>     Is this an issue to be dealt with by the rtl-sdr folks?
>> I suspect that the rtl-sdr package caused the new group to be applied to the devices without
>> consideration for other users of these devices.
>> I will raise this conflict on the fedora list, however mythtv is from @rpmfusion and rtl-sdr is from @fedora.
> This is a conflict between the rtl-sdr package and the MythTV
> packages.  If you are not using the SDR software, you should just
> remove the SDR packages.  If you do want to use the SDR software, you
> will need to work out some arrangement that gives MythTV access to the
> tuners.  Adding the frontend user and backend user ("mythtv") to the
> "rtlsdr" group is an option that should work.

This is my plan B.

> Another option is to do
> chmod a+rw on all the tuner devices.

Done that, and added the chmod command to rc.local too.

> However, MythTV does need
> exclusive access to the tuners when it is using them.  So if the SDR
> software is using them when MythTV wants to, MythTV will fail to
> access the tuners.  And in MythTV you have to set the option on each
> tuner that makes MythTV release access to it when it is not using it.

Sure. I plan to dedicate one tuner (there are 5) to rtl-sdr if I use it.

> And you need to turn off EIT use of the tuners, otherwise MythTV will
> use them for EIT EPG grabbing when it is not using them for recording.

EIT is already set to run on only one tuner.

> It would be much easier just to remove the SDR packages.

True, and should be trivial to install (with due care) when needed.

However, the general solution should be something that fedora users are unlikely to trip over.
Right now installing rtl-sdr will make mythbackend fail which may not be trivial to diagnose
(took me a while to realize what happened).


Eyal Lebedinsky (eyal at eyal.emu.id.au)

More information about the mythtv-users mailing list