[mythtv-users] /dev/dvb permissions

Stephen Worthington stephen_agent at jsw.gen.nz
Mon Jun 28 04:16:29 UTC 2021

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.  Another option is to do
chmod a+rw on all the tuner devices.  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.
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.
It would be much easier just to remove the SDR packages.

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