[mythtv-users] Mythfrontend can't ping database host

[Gabe Rubin]

On Mon, Dec 31, 2012 at 6:38 AM, Michael T. Dean <mtdean at thirdcontact.com>wrote:

> On 12/27/2012 02:17 AM, Bill Meek wrote:
>
>> On 12/26/2012 11:20 PM, Nick Rout wrote:
>> ...
>>
>>>  Quoting Gabe Rubin:
>>>>>>>
>>>>>>>  Cannot find (ping) database host 192.168.1.101 on the network
>>>>>>>>
>>>>>>> ...
>>
>>> Actually it has everything to do with mysql. It is the details myth needs
>>> in order to log in to mysql, which it has to do pretty well as soon as it
>>> starts.
>>>
>>
>> Hi;
>>
>> Sorry, it's not an issue with the database.
>>
>> The diagnostic Gabe posted originally, comes from a simple ping
>> to the box that hosts the database. See:
>>
>>     http://code.mythtv.org/cgit/**mythtv/tree/mythtv/libs/**
>> libmyth/mythcontext.cpp#n630<http://code.mythtv.org/cgit/mythtv/tree/mythtv/libs/libmyth/mythcontext.cpp#n630>
>>
>> His error message prints below at line 682. I guessing he's running
>> on 0.25 since he references mysql.txt. Not so subtle hint to everyone
>> that it's nice to mention the version you're running on.
>>
>> The test of the connection to the database happens on line 693. He also
>> stated that without the ping, the frontend works.
>>
>> That's why I suggested running the frontend with -v system --loglevel
>> debug.
>> It will print what happens when ping() runs the system call. He's already
>> said he can ping the machine both from itself, and from a remote host.
>>
>> So, if the command line ping works, then we need to see what's actually in
>> the command being executed.
>>
>> As to why the ping is even being done at all, I believe it's because
>> DBHostName=192.168.1.101, rather than 127.0.0.1, localhost or the
>> value returned by the hostname command. Any one of the three would
>> prevent the ping.
>>
>>
> Yes, Bill is exactly correct.  MythTV uses the ping system utility, not
> mysqlping, to test to see if some host exists at the address specified.
>  It's a very simple (though not super reliable) test performed since MythTV
> will not run without a valid database, so it can't run if it can't talk to
> the host with the database.
>
> Note, also, that the ping utility is generally something that requires
> root permission in modern Linux systems.  This is generally handled for
> non-root users either by setting the sticky bit (which is ugly--and can
> result in an exploit finding a way to get root access to the system) or a
> capability allowing the process to send arbitrary packets to the network.
>  So, I recommend you check your ping command:
>
> ls -l /bin/ping
>
> and if the sticky bit isn't set, try:
>
> /sbin/getcap /bin/ping
>
> and if it doesn't show:
>
> /bin/ping = cap_net_raw+ep
>
> you should do:
>
> sudo setcap cap_net_raw=ep /bin/ping
>
> and if that doesn't work, you need to get your distro to properly fix the
> ping utility (either by enabling capabilities on the file system or
> whatever they feel is best :).
>
> Note, also, that using a DB address that is not localhost, when on the
> same host, will result in seriously degraded database performance versus
> localhost.  Using Unix sockets (which is done automatically when you
> specify localhost for the MySQL server) is much faster than using TCP/IP
> networking (which is done for routable addresses.
>
> While we say that you cannot have localhost or 127.0.0.1 anywhere in your
> MythTV system configuration when you're using multiple hosts in a MythTV
> system, you can use localhost in your MythTV database configuration on the
> MythTV host that is also the MySQL host--and, generally, may want to for a)
> much better communications performance, especially for large results, and
> b) better reliability (because it no longer depends on system networking
> support--which is especially nice for these distros with "managers" that
> like to pull the plug on all networking every time there's a blip in the
> connection or whatever).
>
> If you have only one system, though--i.e. the database is always at
> localhost because you run your single combined frontend/backend system on
> the same host as your MySQL server--you can just change the DBHostName to
> localhost (or 127.0.0.1) and it will fix the issue and may result in much
> better performance, too.
>
> Mike
>
>
"Fixing" ping seemed to do the trick.  My FE and BE are on a combined
system and I don't intend to any more mythboxes to my setup.

I have modified my ~/.mythtv/msql.txt file so it now reads
DBHostName=192.168.1.101

Thanks for the tip.
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