[mythtv-users] Remotely monitor Backend is running

[Stephen Worthington]

On Fri, 8 Oct 2021 18:54:04 -0500, you wrote:

>
>Hi Folks!
>
>
>Trying to create a script to let me know when my MythTV Backend is not 
>running. What I have works, but apparently only if totally off-line (as 
>in off). This morning not quite sure what happened but the Frontend 
>could not find the Backend (glanced at the screen, knew it was a BE 
>issue). Accessing the webpage (Firefox to 192.168.4.3:6544) the “last 
>10” rotating display was not present, fairly certain the ‘Current Tuner 
>Activity” listing was present; ‘Frontend Status” was definitely present. 
>(Probably unnecessary information, but in case help
.)
>
>
>What I current have follows; cron on the computer my rump is usually in 
>front of has a script which inquires the Backend every 15 minutes during 
>the day. If no problem no notification; if there is a problem a popup 
>appears on my screen. Works if the MythTV is totally off, but did not 
>notify with the above situation. I also prefer the pop-up over an e-mail 
>notification.
>
>
>The nitty-grity so far:
>
>
>The Backend is at 192.168.4.3.
>
>
>crontab on my computer:
>
>
># Test Backend 3 (BE3) is on-line every 15 minutes from 6:00 a.m. to 
>7:45 p.m.
>
># The script does not display except with a problem
>
>*/15 07-19 * * * export DISPLAY=:0 && /bin/sh '/home/barry/MythTV 
>Backend Scripts/Test_BE3.sh'
>
>
>==> barry at NZXT:~$ cat '/home/barry/MythTV Backend Scripts/Test_BE3.sh'
>
>#!/bin/sh
>
>
># Test Backend 3 (BE3) 192.168.4.3
>
>#
>
># Test cmd line for make appear off-line: search for " nc -z "
>
>#
>
>#####################################################################
>
># Create variables
>
>current_date_time=$(date)
>
>
>#####################################################################
>
># Test connection -- port 6544 is default -- use 8080 for off-line test
>
>nc -z 192.168.4.3 6544
>
>if [ $? -eq 0 ]
>
>then
>
>echo "BE3 is up."
>
>else
>
>echo "exit status is $?."
>
>echo "BE3 192.168.4.3:6544 down."
>
>Err_BE3_1="Oh-oh!! MythTV Backend 3 (BE3 - 192.168.4.3) is down! "
>
># XMsg_Size=" -fn '-*-*-*-r-*--0-150-0-0-p-*-iso8859-1'"
>
># Why this works in one script and not another -- bug
>
># XMsg_Size=" -fn '-*-*-*-r-*--0-200-0-0-p-*-iso8859-1'"
>
># echo "$current_date_time\n $Err_BE3_1\n" | xmessage $XMsg_Size -file -
>
>echo "$current_date_time\n $Err_BE3_1\n" | xmessage -fn 
>'-*-*-*-r-*--0-200-0-0-p-*-iso8859-1' -file -
>
>
>fi
>
>
>exit
>
>
>
>I don’t know what netcat’s -z switch does – saw it when cookbooking 
>another project and seemed to do what I needed. ..Something about not 
>sending data (which is probably good as I saw something about a lot of 
>pings could lock up MythTV).
>
>
>Thanks!
>
>Barry

The nc -z option tells nc to do a TCP connection without sending any
data - it just disconnects again.  I ran Wireshark to confirm this. So
what it does is send a SYN, gets a SYN,ACK reply, sends an ACK, sends
a FIN,ACK, gets an ACK reply.  Just TCP setup and disconnect packets,
with no data in them.  So what is being tested is that there is a
program that is accepting TCP connections on port 6544.

It might be better to actually use the MythTV API and, for example,
request the next recording time, as that would check that a lot more
of mythbackend is working.  It is better to use Python for that, as
there is API support for Python.  I have code to do that as part of my
gaps program:

http://www.jsw.gen.nz/mythtv/gaps

which is probably a reasonable example of a real life use of that API
call, so you could just take a copy of gaps and cut out all the extra
code to just leave a call to Dvr/GetUpcomingList and check the results
and then return 0 for OK or an error code from that.  However, that
requires that you know at least a bit of Python.  If you would like me
to do a cut down version like that, let me know.