[mythtv-users] Remotely monitor Backend is running

[James]

> On 9 Oct 2021, at 1:09 pm, Stephen Worthington <stephen_agent at jsw.gen.nz> wrote:
> 
> 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.

It is *very* easy to do this sort of stuff with systemd.

I offer 2 examples:

[Unit]
Description=MythTV backend service
After=network.target mysql.service
Requires=mysql.service
Wants=apache2.service

[Service]
Type=simple
EnvironmentFile=/etc/sysconfig/mythbackend
User=jam
Group=video
ExecStart=/usr/local/bin/mythbackend --logpath /var/log/mythtv $MYTHBACKEND_OPTIONS

[Install]
WantedBy=multi-user.target

---------------------------------------------------
[Unit]
Description=ssh tunnel to tigger
Requires=network.service

[Service]
ExecStart=/usr/bin/ssh -p 4123 -N -R 1200:localhost:22 -R 4001:localhost:4000 me at tigger.3utilities.com
Restart=always
RestartSec=30
User=doug

[Install]
WantedBy=multi-user.target


Including time qualifications.
In all my years of using myth it has ever 'ceased working' while the myth[front][back]end process 'continues running'
Have fun!
James