1.在/usr/local/nrpe/libexec/目录
vi check_sda3.sh
#!/bin/sh
df_sda3=`/usr/bin/sudo df -k | grep /dev/sda3`
disk_usage_percent=`echo $df_sda3 | awk '{print $5}' | awk -F"%" '{print $1}'`

if [ $disk_usage_percent -lt 60 ]
   then
   echo "OK -disk usage is ${disk_usage_percent}%"
   exit 0
fi
if [ $disk_usage_percent -gt $1 -a disk_usage_percent -lt 80 ]
   then
   echo "Warning -disk usage is ${disk_usage_percent}%"
   exit 1
fi
if [ $disk_usage_percent -gt 80 ]
   then
   echo "Critical -disk usage is ${disk_usage_percent}%"
   exit 2
fi

#chmod +x check_sda3.sh 加上执行权限
#chown nagios:nagios check_sda3.sh

2.在被监控机改nrpe.cfg 定义插件命令.
vi /usr/local/nagios/etc/nrpe.cfg
command[check_sda3]=/usr/local/nagios/libexec/check_sda3

3.在被监控机上测试
# /usr/local/nagios/libexec/check_nrpe -H 127.0.0.1 -c  check_sda3
OK -disk usage is 15%

注：以nagios用户运行df命令，可能无法检查某些文件系统。
如：
$ df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda1             50394964  22551628  25283380  48% /
none                   8311408         0   8311408   0% /dev/shm
df: `/usr/local/httpd/htdocs/': Permission denied
造成下述结果：
# /usr/local/nagios/libexec/check_nrpe -H 127.0.0.1 -c  check_sda3
NRPE: Unable to read output
因此需要修改/etc/sudoers，允许nagios用户以root运行df,且不用输入密码
#visudo

    # Cmnd alias specification
    Cmnd_Alias NAGIOS_CMD=/bin/df
    # User privilege specification
    nagios  ALL=NOPASSWD:NAGIOS_CMD
其中：NAGIOS_CMD必须全部大写，否者会报语法错误。


4.在监控平台机定义命令及服务
define service{
       use                        generic-service
       host_name                  remotehost
       service_description        check_sda3 Space
       check_command              check_nrpe!check_sda3
       }
5. 平台reload nagios
#service nagios restart