Friday, April 8, 2011

CHECK_NRPE: Received 0 bytes from daemon

Verify the check_nrpe error message

Just for testing purpose, let us assume that you are execuing the following check_nrpe command that displays the “CHECK_NRPE: Received 0 bytes from daemon.” error message.

$ /usr/local/nagios/libexec/check_nrpe -H -c check_disk -a 60 80 /dev/sdb1
CHECK_NRPE: Received 0 bytes from daemon. Check the remote server logs for error messages.

If you view the /var/log/messages on the remote host, (in the above example, that is, you’ll see the nrpe error “Error: Request contained command arguments!” as shown below, indicating that check_nrpe is not enabled to take the command arguments.

$ tail -f /var/log/messages
Dec 5 11:11:52 dev-db xinetd[2536]: START: nrpe pid=24187 from=
Dec 5 11:11:52 dev-db nrpe[24187]: Error: Request contained command arguments!
Dec 5 11:11:52 dev-db nrpe[24187]: Client request was invalid, bailing out...
Dec 5 11:11:52 dev-db xinetd[2536]: EXIT: nrpe status=0 pid=24187 duration=0(sec)

Enable check_nrpe command arguments

To enable command arguments in NRPE, you should do the following two things

1. Configure NRPE with –enable-command-args

Typically when you install NRPE on the remote host, you’ll do ./configure without any arguments. To enable support for command arguments in the NRPE daemon, you should install it with –enable-command-args as shown below.

[remotehost]# tar xvfz nrpe-2.12.tar.gz
[remotehost]# cd nrpe-2.12
[remotehost]# ./configure --enable-command-args
[remotehost]# make all
[remotehost]# make install-plugin
[remotehost]# make install-daemon
[remotehost]# make install-daemon-config
[remotehost]# make install-xinetd

2. Modify nrpe.cfg and set dont_blame_nrpe

Modify the /usr/local/nagios/etc/nrpe.cfg on the remote server and set the dont_blame_nrpe directive to 1 as shown below.
$ /usr/local/nagios/etc/nrpe.cfg
Execute check_nrpe with command arguments

After the above two changes, if you execute the check_nrpe for this particular remote host, you’ll not see the error message anymore as shown below.

How to pass arguments to CHECK_NRPE?

$ /usr/local/nagios/libexec/check_nrpe -H -c check_disk -a 60 80 /dev/sdb1
DISK OK - free space: / 111199 MB (92% inode=99%);| /=9319MB;101662;114370;0;127078

Security Warning

Enabling NRPE command line arguments is a security risk. If you don’t know what you are doing, don’t enable this.
Probably by now you’ve already figured out that you can’t blame NRPE if something goes wrong. After all you did set dont_blame_nrpe to 1.

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