Status Monitoring How To

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So, for whatever reason, your Myth processes have occasional crashes that you haven't diagnosed yet (you have submitted a bug report, haven't you?) and you'd like it to restart when it does...

This page has a few approaches to monitoring Myth's processes

Monit

Monit (http://www.tildeslash.com/monit/)

  • It monitors processes and restarts them if they fail.
  • Can be configured to alert you (I like to know if it crashes in case it gets serious!)
  • It is 'secure'able
  • Has a web interface to check status and log
  • Can also monitor anything else (eg listings downloads, disk space etc)

Installation

Debian/knoppmyth install : apt-get install monit

Configuration

  • On Debian create /etc/monit/monitrc
  • On openSUSE create /etc/monitrc
# Monit control file
#
# Comments begin with a '#' and extend through the end of the line.
# Blank lines between program entries are ignored. Keywords are case
# insensitive. All path's MUST BE FULLY QUALIFIED, starting with '/'
#
set daemon  30
set logfile /var/log/monit.log
set mailserver smtp.mydomain.com
set mail-format
 { from: monit@bao.mydomain.com }
set alert root@mydomain.com  # Send alert to system admin on any event
set httpd port 2812 and
    allow ash.mydomain.com
    allow 10.0.0.90
    allow 127.0.0.1
    allow haze.mydomain.com
    allow admin:monit     # user 'admin' with password 'monit'


check process mythbackend with pidfile /var/run/mythtv/mythbackend.pid
 group mythtv
 start program = "/etc/init.d/mythtv-backend restart"
 stop program  = "/etc/init.d/mythtv-backend stop"
 if failed host 127.0.0.1 port 6544 proto http then restart # change if not listening locally
 mode manual
 depends on mysql

check process mysql with pidfile /var/run/mysqld/mysqld.pid
 group mythtv
 start program = "/etc/init.d/mysql start"
 stop program = "/etc/init.d/mysql stop"
 if failed host 127.0.0.1 port 3306 then restart # change if not listening locally
 mode manual

Obviously change the names/ip addresses as needed!

NOTE: It has been reported that mythbackend could crash from repeated pinging of http port (I didn't see anything in my mythbackend log but my backend crashed almost daily until I made the following change). If you find that monit frequently reports failed protocol test, it may be monit causing the problem and you may want to consider commenting out the line:

if failed host 127.0.0.1 port 6544 proto http then restart # change if not listening locally

If you have configured mythtvbackend to be connected from a frontend on another computer on your local network instead of localhost (127.0.0.1), the above (or omitting "host 127.0.0.1" altogether, which will have identical outcome) will fail, since the backend does not listen connections to localhost anymore (only the local ip, like 192.168.X.X). Same applies probably for mysql, too.

If your backend log file starts showing error messages like this:

QSocketDevice::writeBlock: Invalid socket

, then removing the "proto http" in your monit configuration may help also.

Now, sudo monit to start monit.

Note that this tells monit to start in 'manual' mode. To actually start monitoring I have this script in /etc/monit/monit_delay.

sleep 60
monit monitor mythbackend

which is called from the monit init.d script after monit is started. This ensures that when monit starts up it allows enough time for all the other services to get going before it kills them or anything...

Now, check it's all working by connecting to http://yourbox:2812/

You should see a web page.

Now try doing an /etc/init.d/mythtv-backend stop. You should get a mail and the backend should restart.

Now try doing an /etc/init.d/mysql stop. You should get a mail and the backend should stop, mysql should start and then the backend should restart.

Once all this works, you can consider moving on to the next bit...

Paranoia

So what if monit crashes??? asks Craig Partin...

Well, if you like you can run monit from init.

In this case, just put the following line in your /etc/inittab

moni:235:respawn:/usr/sbin/monit

Then init watches and makes sure that monit is running (and if init dies you've got a whole heapload of problems!!) But make sure you don't start monit from your init.d script (but don't forget the monit_delay...)

So, why not run mythbackend like this?
You could - however, it's not the best way to do it - the backend may start before mysql - or your frontend may start before the backend does. For this reason the rc3.d and rc5.d scripts are numbered to start in a certain order to ensure that mysql starts before the backend which starts before the frontend etc.

Daemon Tools

Daemontools (http://cr.yp.to/daemontools.html)

Daemontools is another very similar mechanism that you may prefer. It has the advantage of starting and monitoring the process, so there's no danger of mythbackend starting up before daemontools.


Install

apt-get install daemontools-installer

This will set up your inittab, start the supervise process, and create the appropriate directories (assuming you accepted the defaults during the install). Nothing will start, however, until you create the appropriate files under the /service directory. There's no support in daemontools for service startup order (ie. dependencies), so you have to check in the run script.

Configure

Daemontools looks for a file called /service/servicename/run to start the program. So we'll call our service mythbackend, hence

/service/mythbackend/run
#!/bin/sh

PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
DAEMON=/usr/bin/mythbackend

MYSQLHOST=localhost
MYSQLADMIN=/usr/bin/mysqladmin

if [ -x $MYSQLADMIN ]
then    
        $MYSQLADMIN -h$MYSQLHOST ping &> /dev/null
fi

if [ $? -eq 0 ] # ping worked
then
        exec $DAEMON --logfile /var/log/mythtv/mythbackend.log
else    
        logger "Mysqld not running yet. Waiting..."
fi

As soon as you make this file executable supervise will try and start up mythbackend, so make sure you've stopped the existing process (eg: /etc/init.d/mythbackend stop) and removed the existing startup script (I moved mythbackend from /etc/init.d/ to </root).

Quick and Dirty

So if all that gets to complicated then try running a script like this (from Will Dorman) periodically from cron:

#!/bin/bash

pidno=$( ps ax | grep mythbackend | grep -v grep | grep -v mythmon)
# echo $pidno
# Checks for pid in "ps" listing, field #1.
# Then makes sure it is the actual process, not the process invoked by this script.
# The last "grep $1" filters out this possibility.
if [ -z "$pidno" ]  # If, after all the filtering, the result is a zero-length string,
then                # no running process corresponds to the pid given.
  echo "No such process running."
  mail <mynumber>@mobile.att.net -s Uh-oh < /tmp/crap
  exit $E_NOSUCHPROCESS
fi

Even Dirtier

A simpler way to see if a process is running is using ps -C <command> and look at the exit code of ps; ps will error if it can't find the process. Much like the Quick and Dirty, this can be run from root's crontab:

*/5 * * * * /root/bin/mythmon || /sbin/service mythbackend restart > /dev/null;

A nice feature of bash is that you can OR two commands together. The second command is tried iff (if and only if) the first command fails. Similarly, ANDing two commands, the second is executed iff the first is successful. /sbin/service is a feature of Fedora/RedHat.

#!/bin/bash
#
# /root/bin/mythmon
# This is run from cron every 5 minutes.
#

ps -C mythbackend > /dev/null && exit 0;

# append message to log file...
# send email notification...

echo "`date +%Y-%m-%d\ %T.%-3N` /root/bin/mythmon: mythbackend not running!!!" \
         >> /var/log/mythtv/mythbackend.log;
exit 1;

Same thing for Mythbuntu

Here is the same code updated for Mythbuntu 0.21. I made changes to support Mythbuntu and to use my own preferred directory for the script (in /root instead of /root/bin). I also added support for mythtv-setup. When mythtv-setup runs it closes the backend. It would be unwise for us to restart the backend while setup is running.

I put the following into /etc/cron.d/mythtv-watchdog (rather than into root's crontab):

#
# monitor the mythbacked service and restart it if it exists
#

*/5 * * * *     root    /root/mythmon || /etc/init.d/mythtv-backend restart > /dev/null;

I changed mythmon to the following (and put it in /root/mythmon instead of /root/bin/mythmon):

#!/bin/bash
#
# /root/mythmon
# This is run from cron every 5 minutes.
#

# check for mythbackend running
ps -C mythbackend > /dev/null && exit 0;

# also check for mytv-setup running (it closes the backend)
ps -C mythtv-setup > /dev/null && exit 0;

# append message to log files ...

echo "`date +%Y-%m-%d\ %T.%-3N` /root/mythmon: mythbackend not running!!!" \
         >> /var/log/mythtv/mythbackend.log;
echo "`date +%Y-%m-%d\ %T.%-3N` /root/mythmon: mythbackend not running!!!" \
        >> /var/log/mythtv/mythmon.log

exit 1;

You will also notice that I append to the standard mythbackend log file and I also write to a private log file just for mythmon. This makes it easy to see when the backend was restarted without having to search through all the mythbackend logs.

Or Quick

This script restarts the mythbackend process right away without polling, sends you an email and creates handy numerated log files.

Notes:

  • This script assumes you have email working on your box (like postfix). If not, just delete the mail line.
  • Run the script at startup, i.e. add "/home/mythtv/gomythbe.sh &" to /etc/rc.local (Fedora)
  • The script will restart mythbackend 10 times before stopping and is a fail safe in case something is really wrong...
#!/bin/bash
#
# Press Ctrl+C to stop the restarting
echo "###############################"
echo "# MythBackEnd Server Starting #"
echo "###############################"
echo To stop the restarting press Ctrl+C when the server is being restarted
echo
trap 'echo; echo $SRV Server Restarter has been STOPPED!; exit 1' 2
C1=0
# Repeat the loop 10 times before exiting
while [ $C1 -le 10 ]
do
  C1=$((C1+=1))
  # Modify the line below to match your server execution command line
  mythbackend > /home/mythtv/mythbackend_$C1.log
  echo "MythBackend server restarted $C1 time(s)!"
  # Send an email - put in your email address!!
  mail -s "MythBackEnd - Process restarted $C1 Times" my@emailaddress.com < /home/mythtv/mythbackend_$C1.log
  sleep 10
done