Having SSH key-exchange issue
 

Hi LQ team.

I'm working on a Nagios setup on CentOS systems, and although I've successfully setup SSH key-exchange before on other production systems, and even yesterday on 2 test systems, I can't seem to get this particular instance to work.

I've looked over this post as well:

http://www.linuxquestions.org/linux/...ation_with_ssh

i've taken the contents of id_rsa.pub from the home directory of the nagios user on each box (/home/nagios/.ssh/id_rsa.pub) and I've placed the data into another file called known_hosts on the other system. So...

ServerA id_rsa.pub > ServerB:../known_hosts
ServerB id_rsa.pub > ServerA:../known_hosts

ServerA: 10.0.100.130
ServerB: 10.0.100.143

If I do this from ServerA:

-- then I get prompted for password, I enter it, and I'm logged into serverB

If I do this from ServerB:

-- it asks if I want to connect to the host, verifying authenticity, etc.. I say, yes, and immediately it connects, no password entered, and I'm logged into serverA.

ownership of everything in ~/.ssh/* is nagios.nagios on both systems.

if you're an experienced Nagios user, the root issue is that I get a "No Route to Host" under Service Status Details for the monitored node. I've done a few checks from nagios server to monitored server, and they run fine, e.g. check_nrpe, check_ssh - and I get successful data returned. not sure if that helps any.

Thanks team.

Permissions also matter. With ssh, using the verbose option repeatedly gives more output and can help you find configuration errors.

Try

ssh -vvvv 10.0.100.143

Please use dsa keys for time being & check with -vvv & send the result...

please also check your authorized_keys file & check if any space is there...

please also confirm file permission of under .ssh directories

Thanks for the replies.

permissions:
ServerA
drwx------ 2 nagios nagios 4096 Nov 9 17:46 .ssh
ls -la
total 28
drwx------ 2 nagios nagios 4096 Nov 9 17:46 .
drwx------ 3 nagios nagios 4096 Nov 9 17:47 ..
-rw------- 1 nagios nagios 409 Nov 8 18:35 authorized_keys
-rw------- 1 nagios nagios 1675 Nov 8 17:22 id_rsa
-rw-r--r-- 1 nagios nagios 409 Nov 8 17:22 id_rsa.pub
-rw------- 1 nagios nagios 3994 Nov 9 17:48 known_hosts


ServerB:
drwx------ 2 nagios nagios 4096 Nov 9 17:46 .ssh

.ssh]$ ls -la
total 28
drwx------ 2 nagios nagios 4096 Nov 9 17:46 .
drwx------ 3 nagios nagios 4096 Nov 9 17:47 ..
-rw------- 1 nagios nagios 409 Nov 8 18:35 authorized_keys
-rw------- 1 nagios nagios 1675 Nov 8 17:22 id_rsa
-rw-r--r-- 1 nagios nagios 409 Nov 8 17:22 id_rsa.pub
-rw------- 1 nagios nagios 3994 Nov 9 17:48 known_hosts

SSH from ServerA
you can see from above, that the key-exchange stops with password prompt


SSH from ServerB
you can see it goes right to ServerA without a problem

@davinders -- when I setup DSA keys, I put the id_dsa.pub into "known_hosts" and it doesnt work. I put the id_dsa.pub into "authorized_keys" and the behavior is still the same. ServerB > ServerA succeeds without issue. ServerA > ServerB still prompts for authentication

FWIW - the previous system admin wasnt utilizing "authorized_keys" file, he was/is using the "known_hosts" entry.

OK, i figured out my issue. Guess I had the wrong id_rsa.pub files criss-crossed or something. I blew away everything in nagios/.ssh -- and ran:

then ran
then I copied the contents of authorized_keys over to ServerB from A, and over to ServerA from B. Appended the contents of ServerA authorized_keys into ~/.ssh/authorized_keys on ServerB, and vice versa.

ran a ssh -vvvv 10.0.100.130 from ServerB -- it works

ran a ssh -vvv 10.0.100.143 from ServerA -- it works.

oh well. its all a learning lesson.

Thanks guys.

now on to figure out more Nagios issues.