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：
[root@mysqldb ~]# /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：
[root@mysqlvm2 ~]# /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;;;
[root@mysqlvm2 ~]#
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。