How do I skip the "known_host" question the first time I connect to a machine via SSH with public/private keys?

Question

How do I skip the "known_host" question the first time I connect to a machine via SSH with public/private keys?

Solution 1

All the other current answers are missing the UserKnownHostsFile=/dev/null

If you just want to do it once you can use:

ssh -o StrictHostKeychecking=no hostname

If you want to do it repeatedly you should add something like the following to your ~/.ssh/config

Host 192.168.0.*
    StrictHostKeyChecking no
    UserKnownHostsFile=/dev/null

To configure this on OpenSSH for Windows simply replace /dev/null with NUL.

Good explanation from: http://linuxcommando.blogspot.com/2008/10/how-to-disable-ssh-host-key-checking.html

Solution 2

Turn StrictHostKeyChecking off via ssh_config or command line options.

Solution 3

You can get the public key, add it to known_hosts file and then rehash it:

ssh-keyscan -t rsa hostname >> .ssh/known_hosts
ssh-keygen -H
rm .ssh/known_hosts.old

Solution 4

This took me a while to find. The most common usecase I've seen is when you've got ssh tunnels to remote networks. All the solutions here produced warnings which broke my scripts (nagios).

The option I needed was:

NoHostAuthenticationForLocalhost yes

Which, as the name suggests also only applies to localhost.

Solution 5

$ ssh -o StrictHostKeychecking=no hostname

This will cause the check to be skipped and the remote host's key to automatically be added on first login. (There's also the option CheckHostIP, but it doesn't seem to actually disable the check for whether a key exists at all).

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Comments

[Jason Axelson]

Why was this marked as the duplicate when it predates the other question?

[Doug Harris]

/etc/ssh/ssh_config or ~/.ssh/config --- or whatever the equivalent is on windows if that's your client platform

[metavida]

I also like to use UserKnownHostsFile so that the signature isn't remembered on my system. A nice trick: ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeychecking=no hostname

[vonbrand]

You do know what kind of attack this question is supposed to prevent, do you?

[Adam Lewis]

I've been hunting for away to filter out a subnet for months (not actively), this is exactly what I've been wanting. We have a small development network with dhcp and our devices are always getting new IP address, this making connecting to them MUCH easier. Thanks!

[nethero]

This answer should be nuked back to the stone age and wiped from existence. Can someone actually delete it?