[mythtv-users] /dev/dvb permissions
John Pilkington
johnpilk222 at gmail.com
Mon Jun 28 16:07:41 UTC 2021
On 28/06/2021 06:27, Eyal Lebedinsky wrote:
>
>
> 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).
>
> cheers
>
I see this is also on the Fedora lists.
I'm running mythtv master with dvb tuners in Fedora 33. No similar
problem seen. rtl-sdr is installed, but I don't have its target device.
Perhaps you do?
rtl-sdr is 'SDR utilities for Realtek RTL2832 based DVB-T dongles' which
can 'turn your ... dongle into an SDR receiver'
John P
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