Munin
Munin is a networked resource monitoring tool that can help analyze resource trends and bottlenecks. Munin has a master/node architecture in which the master regularly fetches the data from the nodes and presents the information in graphs through a web interface. A default installation provides a lot of graphs with almost no work and new graphs can be easily created added as plugins. [1]
You can check out OpenStreetMap's Munin install for an example.
Installation
Install the munin package on the master machine and munin-node on the devices that you whish to monitor.
You can also install them both on the same machine so that the master machine monitors itself.
Further documentation may be found on the Munin documentation wiki.
Configuration
Munin master
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.
The following example uses /srv/http/munin
, 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
Cron
crontab
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 the email server to send mails to the munin user. If using postfix, add the following:
/etc/postfix/aliases
munin: root
And run:
# 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
Now, reload systemd configuration, enable/start munin-cron.timer
and verify that everything is working:
# journalctl --unit munin-cron.service # less /var/log/munin/munin-update.log
Permissions
When graph_strategy cgi
is enabled in /etc/munin/munin.conf
ensure the directory /var/lib/munin/cgi-tmp
is owned by user and group munin
so that the /usr/share/munin/cgi/munin-cgi-graph
script is able to write the png files to this directory.
# chown munin: /var/lib/munin/cgi-tmp
Testing
Once munin-cron
is configured to run Munin will be ready to start generating graphs. Ensure the munin-node.service
is running on each of the nodes. It may be useful to jump ahead to the #Munin node section and return here once the node are up and running.
By runnning the munin-cron
command manually as the munin
user, it will trigger the generation of HTML and graph images immediately without having to wait for the next cron run:
[munin]$ munin-cron
If the munin logging is configured, the logs are usually found in /var/log/munin/
. Watching the munin-update.log
log in a seperate terminal after running the munin-cron
command can be helpful in diagnosing issues.
# tail -f /var/log/munin/munin-update.log
And finally test the interface by pointing your browser to the output directory or http://localhost/munin/.
Munin node
Daemon
On the nodes, enable/start munin-node.service
.
IPv6
For IPv6 support on munin-node, using:
/etc/munin/munin-node.conf
host :::1
Install:
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 hostname. 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.
Plugins
Run munin-node-configure
with the --suggest
option to have Munin suggest plugins 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
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>_<device>
to be used on <device>
. See the if_
plugin for an example.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.service
. Finally, refresh the web page.
Additional 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 Developing Plugins at the Munin documentation wiki to learn how.
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 example notice, that the plugin apache_accesses
gives no output at all, when enabled. In order to run the plugin directly:
# munin-run apache_accesses
The following 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, install the missing library, in this case, perl-libwww.
Permissions
Because many plugins read log files, it is useful to add munin
user into log
group:
# usermod -a -G log munin
Web server (optional)
This 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 will need to install and configure one of the following web servers:
Or one of the other servers found in the web server category.
Apache
Apache VirtualHost examples
Based on information found here:
- http://guide.munin-monitoring.org/en/stable-2.0/example/webserver/apache-virtualhost.html
- http://munin-monitoring.org/wiki/MuninConfigurationMasterCGI[dead link 2021-05-17 ⓘ]
In the next major release of Munin, things will be much simpler. Check it out:
Basic static HTML
<VirtualHost *:80> ServerName localhost ServerAdmin root@localhost DocumentRoot /srv/http/munin ErrorLog /var/log/httpd/munin-error.log CustomLog /var/log/httpd/munin-access.log combined </VirtualHost>
Static HTML with DynaZoom feature
Install perl-cgi-fast.
You must enable one of these:
mod_cgid
(ormod_cgi
if using mpm_prefork_module) by uncommenting the line inhttpd.conf
.- Or install mod_fcgidAUR and add
LoadModule fcgid_module modules/mod_fcgid.so
inhttpd.conf
.
<VirtualHost *:80> ServerName localhost ServerAdmin root@localhost DocumentRoot /srv/http/munin ErrorLog /var/log/httpd/munin-error.log CustomLog /var/log/httpd/munin-access.log combined # Rewrites RewriteEngine On # Images RewriteRule ^/munin-cgi(.*) /usr/share/munin/cgi/$1 [L] # Ensure we can run (fast)cgi scripts <Directory "/usr/share/munin/cgi"> Require all granted Options +ExecCGI <IfModule mod_fcgid.c> SetHandler fcgid-script </IfModule> <IfModule !mod_fcgid.c> SetHandler cgi-script </IfModule> </Directory> </VirtualHost>
DynaZoom Permissions
When Munin cannot draw graphs and logs a similar message to Could not draw graph "/var/lib/munin/cgi-tmp/munin-cgi-graph/"
check to make sure group permissions are set on /var/lib/munin/cgi-tmp/munin-cgi-graph/
so the munin-cgi-graph
directory has writeable group permissions such as drwxrwxr-x 3 munin http 4096 Aug 9 20:11 munin-cgi-graph
.
ls -l /var/lib/munin/cgi-tmp/
If group permissions are not set, then
chmod g+w /var/lib/munin/cgi-tmp/munin-cgi-graph/
Full dynamic
Use this VirtualHost if you want to set html_strategy
and graph_strategy
to cgi
. Page loads will take longer because all the HTML and PNG files will be dynamically generated, but the munin-cron run will take less time because it will not execute munin-html and munin-graph. This feature may become necessary for you if your master polls many nodes and the munin-cron risks taking more than 5 minutes.
Install perl-cgi-fast.
You must enable one of these:
mod_cgid
(ormod_cgi
if using mpm_prefork_module) by uncommenting the line inhttpd.conf
.- Or install mod_fcgidAUR and add
LoadModule mod_fcgid modules/mod_fcgid.so
inhttpd.conf
.
<VirtualHost *:80> ServerName localhost ServerAdmin root@localhost DocumentRoot /srv/http/munin ErrorLog /var/log/httpd/munin-error.log CustomLog /var/log/httpd/munin-access.log combined # Rewrites RewriteEngine On # Static content in /static RewriteRule ^/favicon.ico /etc/munin/static/favicon.ico [L] RewriteRule ^/static/(.*) /etc/munin/static/$1 [L] # HTML RewriteCond %{REQUEST_URI} .html$ [or] RewriteCond %{REQUEST_URI} =/ RewriteRule ^/(.*) /usr/share/munin/cgi/munin-cgi-html/$1 [L] # Images RewriteRule ^/munin-cgi(.*) /usr/share/munin/cgi/$1 [L] <Directory "/etc/munin/static"> Require all granted </Directory> # Ensure we can run (fast)cgi scripts <Directory "/usr/share/munin/cgi"> Require all granted Options +ExecCGI <IfModule mod_fcgid.c> SetHandler fcgid-script </IfModule> <IfModule !mod_fcgid.c> SetHandler cgi-script </IfModule> </Directory> </VirtualHost>
Nginx
Munin 2.0.x
This example Nginx setup is based on a Munin 2.0.x munin
master installation. It requires FastCGI and uses the html_strategy cgi
and graph_strategy cgi
in the munin.conf
configuration.
Install the nginx, perl-cgi-fast and perl-html-template-expr packages on the Munin-Master.
As we will be using the cgi strategy the systemd socket files need to be enabled. So the /run/munin/fcgi-graph.sock
and /run/munin/fcgi-html.sock
sockets are created for the Nginx FastCGI configuration to hook into.
Enable/start munin-graph.socket
and munin-html.socket
.
Create the munin vhost configuration file
/etc/nginx/sites-available/munin
server { server_name yourhost.example.com; listen 80; access_log /var/log/nginx/munin-access.log; error_log /var/log/nginx/munin-error.log info; location ^~ /munin-cgi/munin-cgi-graph/ { fastcgi_split_path_info ^(/munin-cgi/munin-cgi-graph)(.*); fastcgi_param PATH_INFO $fastcgi_path_info; fastcgi_pass unix:/run/munin/fcgi-graph.sock; include fastcgi_params; } location /munin/static/ { alias /etc/munin/static/; } location /munin/ { fastcgi_split_path_info ^(/munin)(.*); fastcgi_param PATH_INFO $fastcgi_path_info; fastcgi_pass unix:/run/munin/fcgi-html.sock; include fastcgi_params; } }
Then restart the webserver (nginx.service
).
If all goes well, point your browser to your host http://yourhost.example.com/munin/
and you should see the Munin Overview page.
Munin 2.1.x
Although Munin 2.1.x versions are not yet available in the Arch repository. It is worth mentioning that the 2.1.x series will no longer use FastCGI and will be replaced with munin-httpd This page already contains an example configuration.
Tips and tricks
MySQL
The MySQL plugin has extra dependencies: perl-dbi, perl-dbd-mysql, 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:
MariaDB> CREATE USER 'muninuser'@'localhost' IDENTIFIED BY 'muninpassword'; MariaDB> GRANT SUPER,PROCESS ON *.* TO 'muninuser'@'localhost'; MariaDB> GRANT SELECT ON mysql.* TO 'muninuser'@'localhost'; MariaDB> FLUSH PRIVILEGES;
To configure Munin to use this new user, create:
/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, install the smartmontools package, and use:
/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#Configuration. 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