check_by_ssh returning UNKNOWN

[Don Badrak]

All,

I just wrestled with this yesterday.  As it turned out, the check worked
just fine from the command line (even as the nagios user).  But, I had
missed a $ in my line ($USER1/check_by_ssh instead of
$USER1$/check_by_ssh).  Dang.

I even tried making a check_by_ssh.sh, writing all the output to a log
file, to see what was going on.  That may help you figure out why it's
getting "UNKNOWN".

On Fri, 9 Jan 2004, Paul L. Allen wrote:

> Rasmus Plewe writes:
>
> > Has anyone seen something like this before and can give me a clue?
>
> If the problematic host is multi-homed and you're referring to it by
> name rather than one of the IPs, this could happen if your ssh has
> strict host key checking set to ask (it is by default) and for certain
> other reasons.  You can test that by:
>
>  1) Login to your monitoring host as user nagios (or whatever your
>  nagios system is running as).  Do not su to nagios from some other
>  user account.
>
>  2) SSH onto each IP address of the box being monitored using the same
>  -l and -i options as in your check command.
>
>  3) Fix whatever SSH complains about (usually the first manual login
>  gets rid of the xauthority message that trips up check_by_ssh).
>
> If the box being monitory has only one IP address then the above tests
> might still shed some light on what may be going wrong.

I've done the following to get it working.

1. Install nagios plugins on remote system (I put them in /usr/local/nagios/libexec)

2. Add nagios user and group on remote system (substitute NNN for your values).
This is for a RedHat Linux system, so put in the proper stuff for your own OS.

      /usr/sbin/groupadd -g NNN nagios
      /usr/sbin/useradd -u NNN -g nagios -c "Nagios" -d /home/nagios -s /bin/bash nagios

3. Set up the .ssh directory and key on remote system

   (on remote host)
      mkdir /home/nagios/.ssh
      chown nagios.nagios /home/nagios/.ssh

   (copy key into /home/nagios/.ssh/authorized_keys)

The key has these options (put in your own monitorhost name(s) and IP(s)), followed
by your own key.

from="monitorhost.domain,192.168.0.1",no-port-forwarding,no-X11-forwarding,no-agent-forwarding,no-pty ...

4. Create the file for the nagios user in $HOME/.ssh/config on the local system

      Host *
         ForwardX11 no

This stops the generation of the xauthority Paul talks about in his step #3.

5. Establish the known_hosts entry on the local system from the nagios user.  I
do this with sudo. I didn't have any troubles with this, as the -H says to use the
home directory of the user (so it picks up the right place to write the known_hosts file).

      sudo -u nagios -H ssh nagios@(remotesystem) 'uname -a'

You should do this for (remotesystem) by DNS name and by all IP addresses by which
it is known in the Nagios configuration (as Paul says in his step #2).

I'd recommend trying the same line you'll use from your command.cfg
file under the same nagios user.  That might shed some light on the
problem.  Or just confuse you more.

Don
-- 
Don Badrak <dbadrak at census.gov>              301.763.5534 work
Telecommunications Office                    301.457.4438 fax
U.S. Bureau of the Census
Suitland MD, USA


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