when I test the nagios at the first time,I met the problem ,the message is :
can't open the file which needs updates.The rights of external commands file or directory is incorrect,set up the correct rights according to the FAQ.
Then I find a article about how to solve the problem.
http://liucb.blog.运维网.com/3230681/590627
I change the rights of the file “/usr/local/nagios/var/rw/nagios.cmd”.Add the write rights on the file.then the problem disappeared.
It's a special file and wired.I can't open it. and this guy said it could't be copied.If it is not exist,you create it by yourself.