[mythtv-users] Which SystemD script?

Leo Butler leo.butler81 at googlemail.com
Mon May 9 11:09:15 UTC 2022


On Fri, Apr 29 2022, Stephen Worthington <stephen_agent at jsw.gen.nz> wrote:

> On Thu, 28 Apr 2022 06:13:42 -0500, you wrote:
>
>>That's a good tip, but it may not be needed. I have the same
>>mythtv-backend.service file as the OP in that thread and I have never
>>had an issue with my hdhr tuner being marked as unavailable.
>
> Until it happens.  It is a race condition - it is likely that there is
> something in your system that makes mythbackend start late enough that
> networking is up.  Most of the time.  But with race conditions,
> eventually something happens that changes the timing, and then
> mythbackend starts earlier and the tuner is not found.  Things that
> affect the timing fairly drastically are fscks being run on partitions
> at startup, which will happen from time to time if you are using ext
> format partitions, or if you have a power failure and the partitions
> are still marked as dirty on the next boot.  Or some random program
> that used to hold things up for a while gets a new version that makes
> it work faster.  Or a new version of systemd gets installed that runs
> something in parallel that used to run in sequence.  Or you upgrade to
> Ubuntu 22.04 LTS and the timings have changed and you always get
> mythbackend starting too early.  That is the nature of race conditions
> - some systems will see the problem on almost every boot, and others
> will not see it except maybe once in the lifetime of the system.
>
> So, have you ever had a problem where mythbackend did not seem to be
> working and you restarted it and then it was working?  That is the
> characteristic pattern that you see with this race condition - it only
> happens at boot, so a restart of mythbackend even a few seconds after
> boot will never have it happen.

As I wrote, I have never had such problems.

>
> It really is always better to actually fix race conditions by making
> things happen in the required order, rather than just rely on "its
> working, so why bother?".  Unfixed race conditions will usually bite
> you at some time and it often happens when it will cause real problems
> for you, like when you are trying to work out some hardware problem
> and the race condition also pop up and fools you into thinking that a
> bit of hardware is faulty so you buy a new one that you really did not
> need to.

Yes, the good is the enemy of the best.

TBH, what you are describing sounds like a bug in the systemd service
file that ships with mythbackend. Have you filed a bug report with a
suggested patch (I checked on launchpad, and I don't see anything
there)?

Leo


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