Status Monitoring How To
So, for whatever reason, your Myth processes have occasional crashes that you haven't diagnosed yet (you are trying to diagnose them aren't you?) and you'd like it to restart when it does...
This page has a few approaches to monitoring Myth's processes
Contents
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
# 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.dgreaves.com set mail-format { from: monit@bao.dgreaves.com } set alert root@dgreaves.com # Send alert to system admin on any event set httpd port 2812 and allow ash.dgreaves.com allow 10.0.0.90 allow 127.0.0.1 allow haze.dgreaves.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 start" stop program = "/etc/init.d/mythtv-backend stop" if failed port 6544 then restart 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 port 3306 then restart mode manual
Obivously change the names/ip addresses as needed!
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
and call it 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)
Being OSS, Monit isn't the only game in town - daemontools is another very similar mechanism that you may prefer. Daemontools 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