Ssh-keygen problems

UNIX for Beginners Q & A
1

For some reason, when I try copying my public key to the server, despite it showing as being successful:

rob@linux044:~$ ssh-copy-id -i /home/rob/Work/Keys/keys.txt.pub !@#$%.com
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/home/rob/Work/Keys/keys.txt.pub"
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
Password:

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh '!@#$%.com'"
and check to make sure that only the key(s) you wanted were added.

when I log in and check the two keys I can see clearly they are two different keys. Any idea's what I might be doing incorrectly here?

EDIT: The command I used to copy the key:

ssh-copy-id -i /home/rob/Work/Keys/keys.txt.pub !@#$%.com
2

Have you checked to insure that the permissions are set up correctly?

Is it possible an issue related to file permissions is not allowing overwriting the older key?

3

Well here is something interesting, maybe. I ran ls -l ~/.ssh and there seems to be a few files contained therein: authorized_keys , id_rsa , id_rsa.pub and known_hosts . it would seem my key is being added to the ' authorized_keys ' list but why I wonder is there a file called id_rsa.pub and how do I know which one the host is using. I am still having to enter my password when I ssh onto the network, shouldn't the presence of my public key on that network allow me to log on without a password check?

Also, the authorized_keys file has keys from my other computer and it also has two private keys stored in it?

4

Hi,

authorized_keys does not contain private keys. It only contains public keys. The private key should not leave the source system.

---

You can check what's really going on by increasing the debug level. If there's the wrong key deposited with ssh-copy-id there definitely went something wrong.

Try again with:

ssh-copy-id -o LogLevel=DEBUG1 ....

You can increase LogLevel further to DEBUG2 or DEBUG3 for more intense debugging. So you will definitely see what is going on and what file is used, or maybe rejected. If that's still not enough you may use strace , to trace the systemcalls for opening and reading of ssh-copy-id. But I think that won't be necessary.

id_rsa and id_rsa.pub are the default key files when a keypair is generated. These are the key files which are used if nothing is specified.

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5

On the remote side: . ssh directory permissions should be 700 .

Also on the remote side: $HOME directory also needs to prohibit writing to any file in your remote home tree - 755 or less.. 750, 700 .

Your public key text ( from xxxxxxx.pub ) should exist as one of the keys in the file $HOME/.ssh/authorized_keys on the remote box

6

When the target-servers target-users $HOME/.ssh/authorized_keys does not contain your key (from /home/rob/Work/Keys/keys.txt.pub), it's absolutely clear why key-based auth does not work:

Because your key hadn't been copied or you login with a key that's not permitted.

----

Another Question:

When your public key is /home/rob/Work/Keys/keys.txt.pub. Where's your private key then? Since this is not a standard location you have to configure the Key for the connection to your server.

For example in $HOME/.ssh/config

Host YOUR-SERVER-ALIAS
  Hostname FQDN-HOSTNAME-OR-IP-ADDRESS
  User TARGET-SYSTEM-USER-NAME
  IdentityFile PRIVATE-KEY-FULL-PATH

# Example
Host webserver
  Hostname 192.168.10.2
  User root
  IdentityFile /home/rob/Work/Keys/private-key.txt

Login to your server then via this command:

ssh webserver

Furthermore $HOME/.ssh is a good place to deposit private keys, because it's very restricted by default. And an ssh private key should be protected well from any unauthorized access if possible. And as everybody else says here: Check the permissions! :wink:

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7

So I ran a:

cat ~/.ssh/known_hosts

and there is a rather large text block in that file, why? Is text added here whenever I ssh into a machine? To be clear, I should be storing my key pair's here within the .ssh directory as: id_rsa and id_rsa.pub, is that correct?

8

Hi circuits,

I recommend you to read the ssh manpages...

  • ssh(1)
  • ssh_config(5)
  • sshd_config(5)

There you get a lot of information about the files and usage of ssh. There are a lot of other tutorials on the web too.

Regards,
stomp

1 Like