前言：nagios界面上，看到监控mysql服务报错如下：
Warning：NRPE: Unable to read output
1，去nagios监控服务器上check下
1.1，执行check_nrpe命令远程调用
在监控端nagios服务器上执行check_nrpe检查mysql状态报错如下：
[[email protected] ~]# /usr/lib/nagios/plugins/check_nrpe -H192.xx.180.xx -c check_mysql_status
NRPE: Unable to read output
You have new mail in /var/spool/mail/root
[[email protected] ~]#
1.2，检查下别的check服务
在nagios服务器端检查别的监控项比如check_users，正常如下：
[[email protected] ~]# /usr/lib/nagios/plugins/check_nrpe -H192.xx.180.xx -c check_users
USERS OK - 2 users currently logged in |users=2;8;15;0
[[email protected] ~]#
这里证明，nagios流程是正常的，能检测到别的监控项比如check_users，但是check_mysql故障报错，还是需要去mysql服务器上再去分析问题到底出在哪里。
2，在被监控端mysql服务器check
2.1，调用本地的check_nrpe服务，报一样的错误如下：
[[email protected] ~]# /usr/lib/nagios/plugins/check_nrpe -Hlocalhost -c check_mysql_status
NRPE: Unable to read output
[[email protected]mysqldb ~]#
去单独执行/etc/nagios/nrpe.cfg里面的check_mysql_status命令。
先用cat找到check_mysql的命令行
[[email protected]mysqldb ~]# cat /etc/nagios/nrpe.cfg |grep check_mysql_status
command[check_mysql_status]=/usr/bin/sudo /usr/lib/nagios/plugins/check_mysql -unagios -P3306 -s /usr/local/mysql/mysql.sock -Hlocalhost --password=‘[email protected]‘ -d test
执行，正常显示如下：
[[email protected] mysqldb ~]# /usr/bin/sudo /usr/lib/nagios/plugins/check_mysql -unagios -P3306 -s /usr/local/mysql/mysql.sock -Hlocalhost --password=‘[email protected]‘ -d test
Uptime: 1122870 Threads: 108 Questions: 11559152 Slow queries: 1278 Opens: 3190 Flush tables: 1 Open tables: 395 Queries per second avg: 10.294|Connections=844188c;;; Open_files=49;;; Open_tables=395;;; Qcache_free_memory=209024;;; Qcache_hits=51724c;;; Qcache_inserts=73877c;;; Qcache_lowmem_prunes=5599c;;; Qcache_not_cached=2572345c;;; Qcache_queries_in_cache=1985;;; Queries=11559153c;;; Questions=10724833c;;; Table_locks_waited=0c;;; Threads_connected=107;;; Threads_running=2;;; Uptime=1122870c;;;
[[email protected] mysqldb ~]#
从这里可以看到check_mysql脚本没有问题，是正常的。
2.2，检查下check_mysql的执行权限
[[email protected] ~]# ll /usr/lib/nagios/plugins/check_mysql
-rwxrwxr-x. 1 root root 168272 7月 8 14:54 /usr/lib/nagios/plugins/check_mysql
[[email protected] ~]#
看到是最后一个x，表明有执行权限，sudo到nagios账号，看是否能执行，如下所示：
[[email protected] ~]# su - nagios
-bash-4.1$ /usr/lib/nagios/plugins/check_mysql -unagios -P3306 -s /usr/local/mysql/mysql.sock -Hlocalhost --password=‘[email protected]‘ -d test
Uptime: 1124403 Threads: 106 Questions: 11586454 Slow queries: 1278 Opens: 3190 Flush tables: 1 Open tables: 395 Queries per second avg: 10.304|Connections=846235c;;; Open_files=49;;; Open_tables=395;;; Qcache_free_memory=211696;;; Qcache_hits=51786c;;; Qcache_inserts=73915c;;; Qcache_lowmem_prunes=5732c;;; Qcache_not_cached=2578541c;;; Qcache_queries_in_cache=1890;;; Queries=11586455c;;; Questions=10750088c;;; Table_locks_waited=0c;;; Threads_connected=105;;; Threads_running=2;;; Uptime=1124403c;;;
-bash-4.1$
这里表明既是naigos账号也可以执行check_mysql脚本的，check_mysql脚本路径以及执行权限都没有问题，都是可以的。
2.3，检查sudo的里面的nagios权限配置
Nagios远程调用运行原理是，通过nagios账号来执行所有的check_xxx脚本的，但是我的nrpe客户端是root账号安装的，所以的check_xxx脚本也是root用户所属，nagios在远程调用的时候是否默认执行了su – root，然后在执行check_msyql脚本命令？所以去编辑sudo配置，修改如下，把Defaults requiretty注释掉，然后添加一行nagios ALL=(ALL) NOPASSWD:/usr/lib/nagios/plugins/check_mysql，
vim /etc/sudoers
#表示不需要终端控制
#Defaults requiretty
#表示通过nagios命令执行check_mysql命令不需要密码。
nagios ALL=(ALL) NOPASSWD:/usr/lib/nagios/plugins/check_mysql
修改完，wq!强行保存退出vim编辑，然后执行本次check_npre操作检查，已经恢复正常如下：
[[email protected] ~]# /usr/lib/nagios/plugins/check_nrpe -Hlocalhost -c check_mysql_status
Uptime: 1123659 Threads: 110 Questions: 11573270 Slow queries: 1278 Opens: 3190 Flush tables: 1 Open tables: 395 Queries per second avg: 10.299|Connections=845248c;;; Open_files=49;;; Open_tables=395;;; Qcache_free_memory=227704;;; Qcache_hits=51751c;;; Qcache_inserts=73892c;;; Qcache_lowmem_prunes=5656c;;; Qcache_not_cached=2575554c;;; Qcache_queries_in_cache=1943;;; Queries=11573271c;;; Questions=10737891c;;; Table_locks_waited=0c;;; Threads_connected=109;;; Threads_running=2;;; Uptime=1123659c;;;
再去nagios服务器端执行check_nrpe检查，正常如下：
[[email protected] ~]# /usr/lib/nagios/plugins/check_nrpe -H192.xx.180.xx -c check_mysql_status
Uptime: 1123673 Threads: 110 Questions: 11573464 Slow queries: 1278 Opens: 3190 Flush tables: 1 Open tables: 395 Queries per second avg: 10.299|Connections=845264c;;; Open_files=49;;; Open_tables=395;;; Qcache_free_memory=227704;;; Qcache_hits=51751c;;; Qcache_inserts=73892c;;; Qcache_lowmem_prunes=5656c;;; Qcache_not_cached=2575596c;;; Qcache_queries_in_cache=1943;;; Queries=11573465c;;; Questions=10738069c;;; Table_locks_waited=0c;;; Threads_connected=109;;; Threads_running=2;;; Uptime=1123673c;;;
[[email protected] ~]#
2.4，再去nagios监控界面，查看mysql选项已经恢复正常，如下图所示：
3 附带一些其他原因
引起NRPE: Unable to read output报错的原因有很多种，google了下其它的情况如下：
(1)，客户端配置文件/etc/nagios/npre.cfg里面没有添加nagios服务器IP地址，比如 allowed_hosts=127.0.0.1,IP后面IP没有填写或者填写有误。
(2)，查客户端nrpe的权限是否可读，可被nagios执行，如果nagios权限不够，需要赋予X可执行权限。
(3)，nrpe.cfg里面commands命令路径是否正确，比如有些既有rpm方式安装的也有源码安装的，两者路径不一样，源码安装ngios客户端路径是/usr/local/nagios/libexec/check_mysql，而rpm包安装路径是/usr/lib/nagios/plugins/check_mysql。
来自： http://blog.itpub.net/blog/post/id/1217246/
参考文章：http://blog.csdn.net/kakane/article/details/9615795
Nagios监控MySQL报错：NRPE: Unable to read output的详细解决过程