Mythbackend

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The backend process (mythbackend) is the portion of the system that handles the Video capture cards as well as Scheduling Recordings on those cards, Commercial Detection, and transcoding. The backend process interacts with the Database primarily.

As with the mythfrontend, there can be multiple backends. One backend process is designated as the master backend. This is usually the first backend installed on a system. This backend is responsible for coordinating the activities of the other backends known as slaves. This is especially true for scheduling as the master backend will determine the best distribution of programs across all available tuners. Each backend can have any number of tuners. A machine that does not have any tuners attached can store and serve content by running mythmediaserver instead of mythbackend. Commercial Detection can be distributed across multiple backends, and other machines running mythjobqueue, thereby spreading the load of that process.

There is no requirement for direct user interaction with the backend. The backend can use local HardWare/File Storage or have it mounted from another system. If remotely mounted, network performance should be considered as there will be considerable traffic on the network as recordings are stored and retreived by the backend process.

Command Line Options

Valid options are summarised below:

-h or --help or --usage        Display this help printout, or give detailed information of selected option.
-p or --pidfile                Write PID of mythbackend to filename
-d or --daemon                 Runs mythbackend as a daemon
--user                         Drop permissions to username after starting
--noupnp                       Disable use of UPnP
--printexpire                  List of auto-expire programs
--printsched                   Upcoming scheduled programs
--testsched                    Test run scheduler (ignore existing schedule)

Logging Options:
--enable-dblog                 Enable logging to database.
--loglevel                     Set the logging level.
--logpath                      Writes logging messages to a file in the directory logpath.
--nologserver                  Disable all logging but console.
-q OR --quiet                  Don't log to the console (-q).  Don't log anywhere (-q -q)
--syslog                       Set the syslog logging facility.  Set to "none" to disable, defaults to none.
-v OR --verbose                Specify log filtering. Use '-v help' for level info.

Communications Protocol

The mythbackend and mythfrontend communicate using their own Myth Protocol. Work on defining the Myth Protocol is being performed on this Wiki.

Troubleshooting

Mythbackend uses the logging routines shared by the rest of MythTV, and the command line options defined there can be used to control where and what debugging information is logged.

Need to add backend-specific troubleshooting help here, or at least link to Troubleshooting

Interpreting --printsched Output

The --printsched command line option prints out upcoming scheduled recordings.

This format is also used in mythbackend logs of scheduling activity (with -v schedule), and is particularly useful when obtaining schedule data with --testsched.

For example:

Title - Subtitle                    Ch Station Day Start  End   S C I  T N Pri
Ask This Old House - "Installi     21_2 WLIWDT2 13 16:30-17:00  1 1 1  A 1 0
The Simpsons - "Treehouse of Horro   11 WPIX    13 19:00-19:30  1 0 0  A R 0

Title, subtitle, channel (number), station (callsign), day, start (time) and end (time) are rather straight forward. The meanings of the other columns are:

  • S - Source ID
  • C - Card ID
  • I - Input ID
  • T - Recording Type Character
  • N - Recording Status Character
  • Pri - Priority

The meanings of the Recording Type Character (T) are:

  • S - Single record
  • T - Timeslot
  • W - Weekslot
  • C - Channel
  • A - All
  • F - Find one
  • d - Find one daily
  • w - Find weekly
  • O - Override or Don't record

The meanings of the Recording Status Character (N) are:

  • A - Aborted
  • R - Recorded / Current recording
  • X - Don't record
  • P - Previous recording
  • E - Earlier showing
  • T - Too many recordings
  • c - Cancelled
  • M - Missed
  • C - Conflict
  • L - Later showing
  • r - Repeat
  • x - Inactive
  • K - Low disk space
  • B - Tuner busy
  • f - Failed
  • N - Not listed
  • V - Never record
  • F - Offline
  • O - Other showing
  • (a number) - the card ID on which the show is currently recording