check_log problem on x86_64 - NRPE:Unable to read output


We have a fairly large nagios setup, running the standard Fedora nagios packages. E.g. nagios-2.9-1.fc6, nrpe-2.7-3.fc6.

The strange thing is for some reason, the our x86_64 based clients are unable to run the check_log NRPE client. The master is reporting, “NRPE: Unable to read output”.

Note that in our setup, the nagios server is running on a i686, FC6. On our i686 client machines, everything works fine. I.e., all NRPE clients work.

On the x86_64 client machines, all NRPE commands work: LOAD, PROCS, FREE_SPACE, etc., but NOT check_log. We have checked permissions, etc. On the client machines:

su - nagios

$ sudo /usr/lib64/nagios/plugins/check_log -F /var/log/messages -O ~/check_log.messages.old -q “some error string”

Log check ok - 0 patter matches found

However, when the NRPE server tries to do this, we see the “NRPE Unable to read output” error. It is also clear that the client check_log is not even running because the -o output file is not being updated.

One further note, our nrpe client is run under xinetd. Again, all other NRPE commands are working.

Any ideas?

Halloo Support


add this to your sudoers file on the clients you want to run check_log on:

nagios ALL=(ALL) NOPASSWD: /usr/lib64/nagios/plugins/check_log

And try again. If it still doesn’t work, remember your nrpe config on the client should have the sudo in it. eg:
command[check_my_logs]=sudo /usr/lib64/nagios/plugins/check_log -F /var/log/messages -O ~/check_log.messages.old -q “some error string”

lemme know if that works


Dear MP,

Our sudoers file is already correct. In the first post you can see that we tested that by changing to the nagios user “su - nagios”, and then running the command as nagios: “sudo /usr/lib64… etc”


Found the answer! Looking at /var/log/secure, the problem reveals itself. The answer is here: … =82503&l=2

Basically, for some reason, the x86_64 version of Fedora has has

Default requiretty

in its /etc/sudoers file. Commenting this out fixes the problem!

Halloo Support


thanks for coming back to post your solution!