event handlers on remote host

[Jorge Reyes]

Basic Idea

No-password authentication works because of public key crypto. Let's say you have a local machine Ooga and a remote machine Booga. You want to be able to ssh from Ooga to Booga without having to enter your password. First you generate a public/private RSA key pair on Ooga. Then you send your public key to Booga, so that Booga knows that Ooga's key belongs to a list of authorized keys. Then when you try to ssh from Ooga to Booga, RSA authentication is performed automagically. 

Here are detailed steps on how to do this. 


NOTE: The following examples and scenarios assume you are creating only a single key, e.g. one RSA key or one DSA key. If it turns out that you've created both keys on your (client) system, then you will need to send both of them to the SSH/SSH2 server; otherwise, you may still be asked to enter a passphrase. Thanks to Steve McCarthy for pointing this out. 



  _____  



ssh1

If you're using ssh1, then do this: 

ooga% ssh-keygen -f ~/.ssh/identity 


This will generate a public/private rsa1 key pair. When it asks you to enter your passphrase, just hit return (i.e. leave it empty). Now you need to send your public key to the remote server. 


  ooga% cd .ssh 
  ooga% scp identity.pub user at booga:~/.ssh 


Now you need to log into Booga and add Ooga's public key to Booga's list of authorized keys. 


  ooga% ssh user at booga 


  booga% cd .ssh 
  booga% cat identity.pub >> authorized_keys 
  booga% chmod 640 authorized_keys 
  booga% rm -f identity.pub 


That's it! You can now ssh from Ooga to Booga without entering your password. 



  _____  



ssh2

It's harder for ssh2. There are two common implementations of ssh2: OpenSSH and SSH2. Let's say we want to ssh from Ooga to Booga. If Ooga and Booga both run the same implementation then it's easy. Otherwise, we need to do some extra work to make them talk to each other properly. 

My particular situation is that my local machine is running Windows 2000 with the Cygwin tools and OpenSSH 3.2.x. The remote machines may either have OpenSSH or SSH2. I'll cover these two cases below. 



  _____  


ssh2: Ooga = OpenSSH, Booga = OpenSSH

First, generate a public/private DSA key pair on Ooga. 

  ooga% ssh-keygen -t dsa -f ~/.ssh/id_dsa 


When you are asked for a passphrase, leave it empty. Now send the public key to Booga. 


  ooga% cd .ssh 
  ooga% scp id_dsa.pub user at booga:~/.ssh 


Next, log in to Booga and add the public key to the list of authorized keys. 


  ooga% ssh user at booga 


  booga% cd .ssh 
  booga% cat id_dsa.pub >> authorized_keys2 
  booga% chmod 640 authorized_keys2 
  booga% rm -f id_dsa.pub 


Note that the filename is authorized_keys2, not authorized_keys. That's it; you're ready to ssh from Ooga to Booga without having to enter a password. 



  _____  


ssh2: Ooga = OpenSSH, Booga = SSH2


First, generate a public/private DSA key pair on Ooga. 


  ooga% ssh-keygen -t dsa -f ~/.ssh/id_dsa 


When you are asked for a passphrase, leave it empty. This key is stored in a format that OpenSSH can use, but SSH2 cannot. You need to export the key to a format that SSH2 understands. 


  ooga% ssh-keygen -e -f .ssh/id_dsa.pub > id_dsa_ssh2_ooga.pub 


Note: the exact flags you need to specify may differ in your case. Check the man pages if the line above doesn't work. Now send the exported public key to Booga. 


  ooga% scp id_dsa_ssh2_ooga.pub user at booga:~/.ssh2/ 


Note: the target directory is .ssh2, not .ssh. Next, log in to Booga and add the public key to the list of authorized keys. 


  ooga% ssh user at booga 


  booga% cd .ssh2 
  booga% cat >> authorization 
  key id_dsa_ssh2_ooga.pub 

  <EOF> 
  booga% chmod 640 authorization



For SSH2, there is an authorization file in which you list the file names of the authorized public keys. Note that this step is different than the case in which Booga is running OpenSSH. Now you are ready to ssh from Ooga to Booga without having to enter a password. 

 

 

 

-----Original Message-----
From: nagios-users-admin at lists.sourceforge.net [mailto:nagios-users-admin at lists.sourceforge.net]On Behalf Of senthil
Sent: Wednesday, September 22, 2004 5:28 AM
To: Demetri Mouratis
Cc: nagios-users at lists.sourceforge.net
Subject: Re: [Nagios-users] event handlers on remote host


And one more help is it possible for some1 to help me 
with the process to setup non-interactive login in SSH ??

regards,
Senthil

Demetri Mouratis wrote:


On Wed, 22 Sep 2004, senthil wrote:



  

Hi,

 I am currently working on using Nagios to monitor a remote host.

Made use of the NRPE plugins to montior the different services on a

remote host.

I tried event handlers and it works fine in the localhost.But if I want

to employ event handlers on a remote machine say to start a HTTP server

when the service moves on to hard state ? what can i do??

    



Setup SSH to allow for non-interactive login to the remote machine and

restart the http daemon.



You'll probably want to configure a way for the nagios user to restart

httpd.  Sudoers would help there.  Otherwise, you'll end up having to SSH

as root to restart it.



Hope that helps.

---------------------------------------------------------------------

Demetri Mouratis

dmourati at linfactory.com





  


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