nagios不检测任何具体数值指示(如操作系统上的进程个数)，它只描述四种被监控对象的状态：OK,WARNING,CRITICAL和UNKNOWN。于是，我们只需要对魔种监控对象的WARNING和CRITICAL状态的阈值进行关注，nagios将阈值传递给插件，由插件负责具体对象的监控以及结果分析，其返回四中状态信息
nagios监控的不同对象的不同方式
linux/UNIX: SNMP,NRPE,send-nsca
switch: SNMP
print: SNMP
windows: SNMP,NSClient++ :它包含nrpe,nsca的功能
nrpe: 0.0.0.0:5666
需要在nagios以及监控对象上同时安装nrpe 以及nagios plugins
nsca:
被动模式，由监控对象主动向nagios发送消息
nsclient++: 是一个客户端,监听在0.0.0.0:12489
安装nagios之前的准备
安装依赖关系:(此处因为需要对mysql进行检测，所以需要安装mysql)
# yum -y install httpd gcc glibc glibc-common gd gd-devel php php-mysql mysql mysql-devel mysql-server
创建用户以及组
# groupadd nagcmd
# useradd -G nagcmd nagios
# passwd nagios
将组附加给apache用户
# usermod -a -G nagcmd apache
编译安装nagios
# tar zxf nagios-3.3.1.tar.gz
# cd nagios-3.3.1
# ./configure --with-command-group=nagcmd --enable-event-broker
# make all
# make install
# make install-init
# make install-commandmode
# make install-config
# make install-webconf
创建一个登陆nagios web的用户
# htpasswd -c /usr/local/nagios/etc/htpasswd.user nagiosadmin
以上配置完成后启动httpd
# service httpd restart
安装nagios插件（nagios检测完全依赖于各种插件）
# tar zxf nagios-plugins-1.4.15.tar.gz
# cd nagios-plugins-1.4.15
# ./configure --with-nagios-user=nagios --with-nagios-group=nagios
# make
# make install
将nagios加入服务并配置为开机启动
# chkconfig --add nagios
# chkconfig --level 345 nagios on
检查配置文件语法是否正确
# /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
启动nagios
# service nagios start
关闭selinux或者设置标签
# chcon -R -t httpd_sys_content_t /usr/local/nagios/sbin
# chcon -R -t httpd_sys_content_t /usr/local/nagios/share
至此，nagios的安装完成，可以通过web进行访问 http://ip/nagios
基于NRPE监控远程linux主机
NRPE用于在远端服务器上运行监测命令的守护进程，它用于让nagios监控端基于安装的方式触发远端主机上的检测命令，并将检测结果输出至监控端，其执行开销远低于ssl，检测过程不需要远程主机上的账号等信息，所以安全性也高于ssh
安装配置被监控端
添加nagios用户
# useradd -s /sbin/nologin nagios
NRPE依赖于nagios plugins,需要先安装
# tar zxf nagios-plugins-1.4.15.tar.gz
# cd nagios-plugins-1.4.15
# ./configure --with-nagios-user=nagios --with-nagios-group=nagios
# make
# make install
安装NRPE
# tar -zxvf nrpe-2.12.tar.gz
# cd nrpe-2.12
# ./configure --with-nrpe-user=nagios --with-nrpe-group=nagios --with-nagios-user=nagios --with-nagios-group=nagios --enable-command-args --enable-ssl
# make all
# make install-plugin
# make install-daemon
# make install-daemon-config
配置NRPE
# vim /usr/local/nagios/etc/nrpe.conf
log_facility=daemon
pid_file=/var/run/nrpe.pid
server_address=127.0.0.1 ;listener address
server_port=5666
nrpe_user=nagios
nrpe_group=nagios
allowed_hosts=172.16.10.1 ;nagios server address
command_timeout=60
connection_timeout=300
debug=0
command[cmd_name]=/usr/local/nagios/
启动NRPE
# /usr/local/nagios/bin/nrpe -c /usr/local/nagios/etc/nrpe.cfg -d
定义一个服务的脚本
vim /etc/rc.d/init.d/nrped
#!/bin/bash
#
# chkconfig: 2345 88 12
# description: NRPE DAEMON
#
. /etc/rc.d/init.d/functions
NRPE=/usr/local/nagios/bin/nrpe
NRPECONF=/usr/local/nagios/etc/nrpe.cfg
case "$1" in
start)
echo -n "Starting NRPE daemon..."
$NRPE -c $NRPECONF -d
echo "done."
;;
stop)
echo -n "Stoping NRPE daemon..."
pkill -u nagios nrpe
echo "done."
;;
restart)
$0 stop
sleep 1
$0 start
;;
*)
echo "Usage: $0 start|stop|restart"
;;
esca
exit 0
服务端配置（nagios监控端）
安装NRPE
# tar -zxvf nrpe-2.12.tar.gz
# cd nrpe-2.12
# ./configure --with-nrpe-user=nagios --with-nrpe-group=nagios --with-nagios-user=nagios --with-nagios-group=nagios --enable-command-args --enable-ssl
# make all
# make install-plugin
检测与监控对象间的连接是否可用
# cd /usr/local/nagios/libexec/
# ./check_nrpe -H 172.16.100.11
NRPE v2.12