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How can I get ssh to temporarily ignore any SSH key-pairs that are present in $HOME/.ssh along with keys that might be loaded in ssh-agent?

NOTE: I don't want to make any changes to my $HOME/.ssh directory by moving SSH key-pair files out of it, nor do I want to edit my $HOME/.ssh/config file, nor remove keys from my keyring (i.e. ssh-agent).

3

I generally do it like so:

$ ssh -o IdentitiesOnly=yes -F /dev/null -i ~/path/to/some_id_rsa root@server.mydom.com

The options are as follows:

  • -o IdentitiesOnly=yes - tells SSH to only use keys that are provided via the CLI and none from the $HOME/.ssh or via ssh-agent
  • -F /dev/null - disables the use of $HOME/.ssh/config
  • -i ~/path/to/some_id_rsa - the key that you explicitly want to use for the connection

Example

$ ssh -v -o IdentitiesOnly=yes -F /dev/null -i ~/my_id_rsa root@someserver.mydom.com
OpenSSH_6.2p2, OSSLShim 0.9.8r 8 Dec 2011
debug1: Reading configuration data /dev/null
debug1: Connecting to someserver.mydom.com [10.128.12.124] port 22.
debug1: Connection established.
debug1: identity file /Users/sammingolelli/my_id_rsa type 1
debug1: identity file /Users/sammingolelli/my_id_rsa-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.2
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.3
debug1: match: OpenSSH_5.3 pat OpenSSH_5*
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-md5 none
debug1: kex: client->server aes128-ctr hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Server host key: RSA f5:60:30:71:8c:a3:da:a3:fe:b1:6d:0b:20:87:23:e1
debug1: Host 'qa03-ost-tesla-h-app01' is known and matches the RSA host key.
debug1: Found key in /Users/sammingolelli/.ssh/known_hosts:103
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /Users/sammingolelli/my_id_rsa
debug1: Server accepts key: pkalg ssh-rsa blen 535
debug1: read PEM private key done: type RSA
debug1: Authentication succeeded (publickey).
Authenticated to someserver.mydom.com ([10.128.12.124]:22).
debug1: channel 0: new [client-session]
debug1: Requesting no-more-sessions@openssh.com
debug1: Entering interactive session.
Last login: Tue Dec  8 19:03:24 2015 from 153.65.219.15
someserver$

Notice in the above output that ssh has only identified the my_id_rsa private key via the CLI and that it uses it to connect to someserver.

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