[mythtv-users] File permissions for recordings

Robert Tsai rtsai1111 at comcast.net
Sun May 22 21:34:25 UTC 2005


On Sun, May 22, 2005 at 09:42:23AM +0100, Derek Scollon wrote:
> Saturday, May 21, 2005, 10:53:36 PM, you wrote:
> > On Sat, May 21, 2005 at 06:35:25PM +0100, Derek Scollon wrote:
> >> Here's an odd problem. I've just recently set up MythTV for the
> >> first time and have been using it for a few days. Yesterday, I
> >> noticed a few programmes recorded where commercial flagging had
> >> failed with an error, unable to open file.
> >> 
> >> I went looking in the recordings folder and thought it might be a
> >> file permissions problem. mythbackend and mtd are both run at
> >> startup as root and mythfrontend is run after logging in as
> >> mythtv. Most of the recordings files were owned by root with file
> >> permissions 644. I changed the existing files' owner and group to
> >> mythtv and set the setuid and setgid bits on the folder with the
> >> intention of making all new files owned by mythtv. The result is
> >> not quite what I expected. Every file since then has its group as
> >> mythtv but its owner is either mythtv or root in a pattern which
> >> seems random, and I can no longer watch any recordings. When I
> >> select a recording in mythfrontend, it takes no action when asked
> >> to play it.
> >> 
> >> I'm assuming this is a problem with what I've done with file and
> >> folder permissions, since I can still watch TV and videos (which
> >> are in a different folder). The question is, with the backend
> >> running as root and the frontend running as mythtv, what should
> >> the file owner and permissions be for recordings? And if the
> >> file's owner is mythtv, why would either the mythtv user or root
> >> have any problem accessing it?
> 
> > This doesn't answer your question, but why not run everything
> > (mythbackend, mtd, mythfrontend) as the mythtv user? You shouldn't
> > need to run any of this as root ...
> 
> You're right, of course, there's no necessity to do it this way. My
> reasons (both of which I realise can be worked around) are...
> 
> 1. Doing it by the method used in the excellent Howto at
> wilsonet.com results in the backend being run automatically at boot
> time as root.

I haven't read this guide that closely. Wouldn't a simple "sudo" cause
the desired program to run as non-root?

> 2. When the backend is run as the mythtv user it can't open the
> frontend on the DVB card. This necessitates changing the permissions
> on /dev/dvb/adaptor0/frontend0, which would need to be done after
> every reboot.

This is solveable by adding the mythtv user to the correct group
(something like the "video" group), assuming your setup is such that
/dev/dvb/... has permissions something like "root:video".

--Rob
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