ssh: "Agent admitted failure to sign using the key"

Solution 1:

just run:

ssh-add + path to key

on the client (your pc)

Solution 2:

This problem involves two machines. WHich was re-booted? ssh-add will only add the key on the client. If the key isn't accepted, there isn't a client error and a server error will only show up if the -v option is used when ssh is invoked on the client, to request the connection.

I suppose its possible too that Ubuntu the package has, for some unknown reason, altered the error message shown. It isn't an error issued by openSSH-server, as it is used in Debian (or anywhere else I've seen it, e.g. RHEL, CentOS, Knoppix, others).

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Solution 3:

My problem was resolved by executing export SSH_AUTH_SOCK=0, as explained in ssh Agent admitted failure to sign using the key on big endian machines on the Ubuntu bug tracker.

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Solution 4:

According to the Ubuntu Bugtracking you mentioned, this is a known bug in gnupg-agent it self. so upgrading to a new gnupg-agent version >2.0.14-1ubuntu1.7 solve the problem.