Nagios on Debian

For monitoring my server I decided to give Nagios a try. The install is very straightforward:

omega:~# aptitude install nagios3-core

This also installs the packages nagios-plugins, nagios-plugins-basic, nagios-plugins-standard and nagios3-common. The only thing Debian specific in the /usr/share/doc/nagios3-common/README.Debian is a note about running external commands from Nagios:

/etc/init.d/nagios3 stop
dpkg-statoverride --update --add nagios www-data 2710 /var/lib/nagios3/rw
dpkg-statoverride --update --add nagios nagios 751 /var/lib/nagios3
/etc/init.d/nagios3 start

A service startup file is added in /etc/init.d/nagios3 and the service is immediately started after the package install:

omega:/etc/init.d# ps xa|grep nagios
14937 pts/0    S+     0:00 grep nagios
24092 ?        SNs    0:00 /usr/sbin/nagios3 -d /etc/nagios3/nagios.cfg

I also immediately got two emails from Nagios, one telling me a filesystem is getting full and one telling me that a lot of processes are running on my server. I knew this last bit already.

Configuration

The main config file is right where I expect it, /etc/nagios3/nagios.cfg. Lots of parameters there, but most very comprehensive and well documented. The configured logfile /var/log/nagios3/nagios.log immediately shows the emailed alerts in a human readable format and the /etc/nagios3/command.cfg immediately shows how I got the emails I got:

define command{
    command_name    notify-host-by-email
    ....

This is just one of the more important command definitions in this file but there are a few others as well, I’m already getting the hang of this thing after 10 minutes or so.

nagios.cfg also sets two config_dir parameters, /etc/nagios-plugins/config and /etc/nagios3/conf.d. These are both directories in which we find several files. The conf.d directory has files that:

• contacts_nagios2.cfg: defines a few contacts
• extinfo_nagios2.cfg: defines host and service information
• generic-host_nagios2.cfg: defines a template for a host
• generic-service_nagios2.cfg: defines a template for a service
• hostgroups_nagios2.cfg: defines generic hostgroups
• localhost_nagios2.cfg: defines an actual host, localhost
• services_nagios2.cfg: defines web service and ssh service
• timeperiods_nagios2.cfg: defines the timings for monitoring

The nagios-plugins/config directory has files that:

• apt.cfg: check apt
• breeze.cfg: wireless?
• dhcp.cfg: check dhcp server
• disk.cfg: check diskspace
• disk-smb.cfg: check SMB
• dns.cfg: check DNS
• flexlm.cfg: check  flexlm
• fping.cfg: check fping
• ftp.cfg: check ftp
• games.cfg: check games
• hppjd.cfg: HP printer?
• http.cfg: check webserver
• ifstatus.cfg: check network interfaces
• ldap.cfg: check ldap server
• load.cfg: check system load
• mail.cfg: check mailserver
• mailq.cfg: check mailserver
• mrtg.cfg: Check mrtg
• mysql.cfg: check MySQL database server
• netware.cfg:
• news.cfg:
• nt.cfg:
• ntp.cfg:
• pgsql.cfg:
• ping.cfg:
• procs.cfg:
• radius.cfg:
• real.cfg:
• rpc-nfs.cfg:
• snmp.cfg:
• ssh.cfg:
• tcp_udp.cfg:
• telnet.cfg:
• users.cfg: