[mythtv-users] no backend loop requires reboot

[Stephen Worthington]

On Mon, 5 Jul 2021 19:27:53 -0600, you wrote:

>If I ever start mythfrontend when I don't have mythbackend running, I am 
>forced to reboot the machine.  Mythfrontend starts a loop where it will 
>fail to find the backend, shut down and restart itself and fail to find 
>the backend again.  The only way I have found to get out of this loop is 
>to reboot.  Is there a better way?
>
>Lloyd

You can just kill mythfrontend.  Is this on Ubuntu?  Ubuntu has a
script that automatically restarts mythfontend if it dies.  So the
"mythfrontend" (/usr/bin/mythfrontend) program is actually a script
file that runs the program "mythfrontend.real"
(/usr/bin/mythfrontend.real).  There are times when you want to kill
mythfrontend.real (because it has locked up while playing a bad video
file, for example).  Then the mythfrontend script will restart
mythfrontend.real.  At other times, such as your case, you probably
want to kill the mythfrontend script first, so that mythfrontend.real
will not be restarted, and then kill mythfrontend.real.

I run MythTV on Xubuntu, and when the Xubuntu desktop (XFCE4) starts,
I have it set up to automatically open two terminal sessions before it
starts the mythfrontend script.  That means if I ever need to kill
mythfrontend or mythfrontend.real, I can just do Alt-Tab to switch to
one of the terminal sessions and do the necessary commands to kill
things.  Alternatively, you can start a new terminal session by doing
Ctrl-Esc to bring up the XFCE4 menu and go to Applications > Terminal
Emulator.  Or you can start a console session outside X using
Ctrl-Alt-F1.  Or you can use ssh from another computer to log in to a
terminal session on the MythTV box.  On recent versions of XFCE4 there
is a bug - the first time after startup that you do Ctrl-Esc, nothing
happens, and you have to do it a second time.

If you are using Ubuntu with a Gnome desktop, then you can do
Ctrl-Alt-T to start a new terminal window.

Once you have a terminal session, you can do this command to find the
mythfrontend programs:

ps -e | grep mythf

This is what I get:

root at mypvr:/usr/bin# ps -e | grep mythf
   3673 ?        00:00:00 mythfrontend
   3703 ?        12:13:00 mythfrontend.re

The "mythfrontend.re" instead of "mythfrontend.real" is because ps has
default size limits for the columns in its output, and has truncated
the name.

Then you can use the number in the first column of the ps output (the
PID = Program ID) to kill it.  First try asking mythfrontend.real to
stop itself by sending it a normal stop request:

kill <PID>

or

kill -SIGTERM <PID>

or

kill -15 <PID>

All three versions of the command do the same thing - they send a
SIGTERM request signal to the program.  The program has to handle a
SIGTERM request and if it does, it will shut itself down in an orderly
manner.  However, all MythTV programs can suffer from a bug where they
attempt to shut down after receiving an external request to do so such
as SIGTERM, but they fail to shut down completely and leave one thread
still running.  So if that happens, you need to repeat the kill
command and the program will shut down that final thread.

If mythfrontend is locked up, it will not be able to receive signals
and will not shut down when requested.  If that happens, you need to
do:

kill -9 <PID>

or

kill -SIGKILL <PID>

This command, unlike most kill commands, does not send a signal to a
program.  Instead it sends a request to the operating system to have
it kill the program.  The system will stop the program instantly - it
will not have any chance to write anything to disk or shut down in any
orderly fashion, so it is always best to try an ordinary kill command
first and only use kill -9 if the program fails to shut down.

Since mythfrontend and mythfrontend.real are normally run from the
same user as you log in as and is used to run the desktop, there is
normally no need to use sudo in front of any of those kill commands.
But if they fail, you can try again using sudo.

If you do not want the mythfrontend script to automatically restart
mythfrontend.real when it stops, you need to kill the script first,
using its PID, before killing mythfrontend.real.

Having had to do all this many, many times, I got fed up and decided
to write a script to automate the process, which I call "killm".  If I
run "killm" it will kill mythfrontend.real using two "kill -15"
commands, and automatically do a "kill -9" if that does not work.  If
I do "killm x" (any text in place of x works), it will kill the
mythfrontend script first.  If you want to install killm from my web
server, run these commands:

sudo su
cd /usr/local/bin
wget http://www.jsw.gen.nz/mythtv/killm
chown root:root killm
chmod u=rwx,og=rx killm
exit