Munin
Munin the monitoring tool surveys all your computers and remembers what it saw. It presents all the information in graphs through a web interface. Its emphasis is on plug and play capabilities. After completing a installation a high number of monitoring plugins will be playing with no more effort.
Using Munin you can easily monitor the performance of your computers, networks, SANs, applications, weather measurements and whatever comes to mind. It makes it easy to determine "what's different today" when a performance problem crops up. It makes it easy to see how you're doing capacity-wise on any resources.
Munin uses the excellent RRDTool (written by Tobi Oetiker) and the framework is written in Perl, while plugins may be written in any language. Munin has a master/node architecture in which the master connects to all the nodes at regular intervals and asks them for data. It then stores the data in RRD files, and (if needed) updates the graphs. One of the main goals has been ease of creating new plugins (graphs). [1]
Simply put, Munin allows you to make graphs about system statistics. You can check out University of Oslo's Munin install to see some examples of what it can do.
Installation
Munin relies on a client-server model. The client is munin-node, and the server is munin (referred as to "munin-master" in the documentation).
You will only need to install munin-master on a single machine, but munin-node will need to be installed on all machines you wish to monitor. This article will focus on a single-machine installation. Further documentation may be found on the Munin documentation wiki.
munin and munin-node
There is currently a munin (munin-master) and a munin-node package in extra.
# pacman -S munin munin-node
Optional web server
The following guide sets up Munin to generate static HTML and graph images and write them in a directory of your choosing. You can view these generated files locally with any web browser. If you want to view the generated files from a remote machine, then you want to install and configure one of the following web servers:
Or one of the other servers found in the web server category.
IPv6
For IPv6 support on munin-node (using host :::1 in /etc/munin/munin-node.conf) you need to install the following packages:
Configuration
Daemon
Start the daemon with
systemctl start munin-node
Enable the daemon with
systemctl enable munin-node
See Daemons for more information.
Plugins
Run munin-node-configure with the --suggest option to have Munin suggest plugins that it thinks will work on your installation:
# munin-node-configure --suggest
If there is a suggestion for a plugin you want to use, follow that suggestion and run the command again. When you are satisfied with the plugins suggested by munin-node-configure, run it with the --shell option to have the plugins configured:
# munin-node-configure --shell | sh
Directories
Create a directory where the munin-master will write the generated HTML and graph images. The munin user must have write permission to this directory.
/srv/http/munin is used below, so the generated output can be viewed at http://localhost/munin/ provided that a web server is installed and running.
# mkdir /srv/http/munin # chown munin:munin /srv/http/munin
Uncomment the htmldir entry in /etc/munin/munin.conf and change it to the directory created in the previous step:
htmldir /srv/http/munin
Customization
Before running munin, you might want to setup the hostname of your system. In /etc/munin/munin.conf, the default hostname is "myhostname". This can be altered to any preferred host name. The hostname will be used to group and name the .rrd files in /var/lib/munin and further, used to group the html files and graphs in your selected munin-master directory.
Cron
Run the following to have munin collect data and update the generated HTML and graph images every 5 minutes:
# crontab /etc/munin/munin-cron-entry -u munin
Configure your email server so that you can receive mails to "munin" user. If you use postfix, add this line in /etc/postfix/aliases
munin: root
And run the command
newaliases
systemd timer
Instead of a cron job a systemd timer can be used.
This needs a service unit configuration:
# /etc/systemd/system/munin-cron.service [Unit] Description=Survey monitored computers After=network.target [Service] User=munin ExecStart=/usr/bin/munin-cron
And a timer unit configuration:
# /etc/systemd/system/munin-cron.timer [Unit] Description=Survey monitored computers every five minutes [Timer] OnCalendar=*-*-* *:00/5:00 [Install] WantedBy=multi-user.target
Finally start and, if everything works, enable munin-cron.timer:
# reload systemd configuration systemctl daemon-reload systemctl start munin-cron.timer # check logs journalctl --unit munin-cron.service less /var/log/munin/munin-update.log systemctl enable munin-cron.timer
Permissions
Because many plugins read log files, it is useful to add "munin" user into "log" group:
# usermod -aG log munin
Testing
Munin should be able to run now. To make sure everything works, start munin-node:
# systemctl start munin-node
Then run munin-cron manually to generate the HTML and graph images:
# su - munin --shell=/bin/bash $ munin-cron
And finally test the interface by pointing your browser to the output directory or http://localhost/munin/.
Plugins
There are many Munin plugins out there just waiting to be installed. The MuninExchange is an excellent place to start looking, and if you cannot find a plugin that does what you want it is easy to write your own. Have a look at HowToWritePlugins at the Munin documentation wiki to learn how.
Adding
Basically all plugins are added in the following manner (although there are exceptions, review each plugin!):
Download a plugin, then copy or move it to /usr/lib/munin/plugins
# cp <plugin> /usr/lib/munin/plugins/
Then link the plugin to /etc/munin/plugins:
# ln -s /usr/lib/munin/plugins/<plugin> /etc/munin/plugins/<plugin>
Now test your plugin. You do not need to use the full path to the plugin, munin-run should be able to figure it out:
# munin-run <plugin>
And restart munin-node:
# systemctl restart munin-node
Finally, refresh the web page.
Removing
If you want to remove a plugin, simply delete the linked file in /etc/munin/plugins - there is no need to remove the plugin from /usr/lib/munin/plugins.
# rm /etc/munin/plugins/<plugin>
Debugging
If you come across a plugin that is not working as expected (for example giving you no output at all) it might be interesting to run it directly. Fortunately there is a way to do this. Following the instructions until here, you will for exmpale notice, that the plugin "apache_accesses" gives no output at all, when enabled. In order to run the plugin directly just run
# munin-run apache_accesses
The error "LWP::UserAgent not found at /etc/munin/plugins/apache_accesses line 86." indicates that a perl function could not be found. To resolve the problem simply install the missing library in this case "perl-libwww".
Tips and Tricks
MySQL
The MySQL plugin has extra dependencies available in the AUR: perl-dbi, perl-cache-cacheAUR, and perl-ipc-shareliteAUR
Additionally it is recommended to access the database through a separate MySQL user. To make another user via the following MySQL commands:
CREATE USER 'muninuser'@'localhost' IDENTIFIED BY 'muninpassword'; GRANT SUPER,PROCESS ON *.* TO 'muninuser'@'localhost'; GRANT SELECT ON mysql.* TO 'muninuser'@'localhost'; FLUSH PRIVILEGES;
To configure Munin to use this new user create the file /etc/munin/plugin-conf.d/mysql_
with the following contents:
/etc/munin/plugin-conf.d/mysql_
[mysql_*] env.mysqlconnection DBI:mysql:mysql;host=127.0.0.1;port=3306 env.mysqluser muninuser env.mysqlpassword muninpassword
S.M.A.R.T.
To enable monitoring of S.M.A.R.T. data, first install the smartmontools package.
Edit or create the file /etc/munin/plugin-conf.d/munin-node
to have the following contents
/etc/munin/plugin-conf.d/munin-node
[smart_*] user root group disk
Then create the appropriate symlink for each disk to be monitored. As an example for sda:
# ln -s /usr/lib/munin/plugins/smart_ /etc/munin/plugins/smart_sda
lm_sensors
Install lm_sensors and configure according to Lm_sensors#Setup. Assuming all goes correctly, create some symlinks:
# ln -s /usr/lib/munin/plugins/sensors_ /etc/munin/plugins/sensors_fan # ln -s /usr/lib/munin/plugins/sensors_ /etc/munin/plugins/sensors_temp # ln -s /usr/lib/munin/plugins/sensors_ /etc/munin/plugins/sensors_volt