how to avoid ssh asking permission?

Question

We are attempting to speed up the installation of oracle nodes for RAC installation. this requires that we get ssh installed and configured so that it doesn't prompt for a password.

The problem is: On first usage, we are prompted for

RSA key fingerprint is 96:a9:23:5c:cc:d1:0a:d4:70:22:93:e9:9e:1e:74:2f.
Are you sure you want to continue connecting (yes/no)? yes

Is there a way to avoid that or are we doomed to connect at least once on every server from every server manually?

Answer 1

You can add the fingerprint to each server's known_hosts. For a single user:

cat ~/.ssh/known_hosts
echo "$SERVER,$PORT ssh-rsa $SERVER_KEY_FINGERPRINT" >> ~/.ssh/known_hosts

Answer 2

Set StrictHostKeyCheking no in your /etc/ssh/ssh_config file, where it will be a global option used by every user on the server. Or set it in your ~/.ssh/config file, where it will be the default for only the current user. Or you can use it on the command line via ssh -o StrictHostKeyChecking=no -l $user $host.

Here's an explanation of how this works from man ssh_config:

 StrictHostKeyChecking
         If this flag is set to “yes”, ssh will never automatically add
         host keys to the $HOME/.ssh/known_hosts file, and refuses to
         connect to hosts whose host key has changed.  This provides max-
         imum protection against trojan horse attacks, however, can be
         annoying when the /etc/ssh/ssh_known_hosts file is poorly main-
         tained, or connections to new hosts are frequently made.  This
         option forces the user to manually add all new hosts.  If this
         flag is set to “no”, ssh will automatically add new host keys to
         the user known hosts files.  If this flag is set to “ask”, new
         host keys will be added to the user known host files only after
         the user has confirmed that is what they really want to do, and
         ssh will refuse to connect to hosts whose host key has changed.
         The host keys of known hosts will be verified automatically in
         all cases.  The argument must be “yes”, “no” or “ask”.  The
         default is “ask”.

Answer 3

I see 2 options:

1) Ignore the HostKeyChecking. For this I use e.g.

ssh -oStrictHostKeyChecking=no -oUserKnownHostsFile=/dev/null user@example.net

2) Add the host's/server's fingerprint to .ssh/known_hosts prior to your first connect.

Of course, option 2 is safer than option 1.

HTH.