Systemd mythbackend Configuration

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Revision as of 14:06, 10 July 2012 by Stevegoodey (Talk | contribs)

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Some newer Linux distributions replace the traditional LSB init script startup management process with a program called systemd, which does things differently; here are some notes on how to make MythTV play nicely with systemd. A cheatsheet from the traditional init scripts to systemd is available on the Fedora wiki pages.

Note that much of the example startup code that follows is based on the rpmfusion packaging of MythTV by Richard Shaw.


Default configuration

Save the configuration file below in /etc/systemd/system/mythbackend.service Changes to files in /lib/systemd/system will be over-written when updated.

Script.png /etc/systemd/system/mythbackend.service


# MythTV backend service

[Unit]
Description=MythTV backend service
After=network.target mysqld.service
# If you intend to use mythweb then
# Uncomment to make sure httpd is started if it is not already.
# Wants=httpd.service

[Service]
Type=simple
# if Type=forking you will need to specify a pidfile so systemd knows
# how to find the eventual process PID, otherwise it presumes that the 
# process being started will be the remaining process

Environment=MYTHCONFDIR=/etc/mythtv
Environment=HOME=/usr/share/mythtv
# or Environment=HOME=/home/mythtv
# the folder containing the .mythtv subfolder containing the config.xml file
User=mythtv
# systemd changes execution from the calling user (possibly root) to this user
# if you have permissions problems or obscure errors try logging in as mythtv


# Uncomment *one* ExecStart, see the 1st note following this box.
# 0.24 and below:
# ExecStart=/usr/bin/mythbackend --logfile /var/log/mythtv/mythbackend.log

# 0.25 and above:
# ExecStart=/usr/bin/mythbackend --syslog local7 
# ExecStart=/usr/bin/mythbackend --logpath /var/log/mythtv
# ExecStart=/usr/bin/mythbackend --daemon --logpath /var/log/mythtv --loglevel crit --pidfile /run/mythbackend.pid

Restart=Restart-always
# whether systemd will continue over-watch and restart on any halt

[Install]
WantedBy=multi-user.target


Important.png Note: Starting with 0.25, there has been a change in the logging. You must adjust the ExecStart line above based on the active release and logging preference (in 0.25 and later.) See: Logging for details.

To enable the backend to start at the next boot, issue the command 'systemctl enable mythbackend.service'. To start the backend immediately, issue the command 'systemctl start mythbackend.service'.

If you specify a log file, all logging will be to that file. If you specify a logpath each program will write to distinctly named files: much better for debugging. Loglevel determines what is logged. Log messages at lower levels will be discarded: In descending order: emerg, alert, crit, err, warning, notice, info, debug. Defaults to info.


Important.png Note: The example runs the backend as user mythtv. You will need to insure that your files/directories/capture cards can be accessed by the mythtv user, or run the backend as root (not recommended).

Delay starting the backend until tuners have initialized

Some tuners take a long time to initialize (typically, firmware loading) and may therefore not yet be available when the backend starts. Since the backend checks for the presence of tuners upon startup, tuner initialization needs to be completed before the backend is started.

This can be accomplished by adding additional Wants= and After= stanza to the unit file, but to have systemd create device units, you must first add a rule to the udev rules directory.


Script.png /etc/udev/rules.d/99-mythbackend

#
# Create systemd device units for capture devices
#
SUBSYSTEM=="video4linux", TAG+="systemd"
SUBSYSTEM=="dvb", TAG+="systemd"
SUBSYSTEM=="firewire", TAG+="systemd"


With the udev rule tag, systemd will create a device unit at startup that one can add to the [Unit] stanza in the startup. Note that one must use the systemd mangled names (generally /dev/some/thing is mangled into dev-some-thing.device). It is highly recommended that you use udev persistent names rather than base names such as /dev/video0.


Script.png device wait code for a typical v4l2 device


Wants=dev-video300.device
After=dev-video300.device


Script.png device wait code for a typical dvb device


Wants=dev-dvb-adapter200-frontend0.device
After=dev-dvb-adapter200-frontend0.device

From mythtv-users post from Richard Shaw

Systemd has a built-in timeout on device units so that startup will not wait forever for a failed device startup.

There are many options for how to run mythbackend with SystemD but one decision you

  • MUST*
  • MUST*
  • MUST*

make is if you're going to run:

Type=simple

or

Type=forking

If you use Type=simple (which is my recommendation) then you *CANNOT* use the "--daemon" option because SystemD is not expecting the daemon to fork!!!

If you use Type=forking then you *MUST* use the "--daemon" option as well as specify a PID file, "--pidfile" in ExecStart *AND* you must set the PIDFile= systemd option so it knows where to find the PID file.

Someone please fix the wiki!

Thanks Richard