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We have a hosted CentOS 6.5 server in which we have a single user account. That account has been configured to use SSH keyfile authentication for the users who need to access it.

I would like to be able to see which keyfile was used to authenticate each login; effectively telling me which end-user logged into the single unix user account. Is there a mechanism for doing so?

  • @MarkPlotnick there is not auth.log on CentOS. – Jakuje Dec 13 '20 at 9:14
  • @Jakuje Thank you. I’ve removed my comment that mentioned that file. – Mark Plotnick Dec 13 '20 at 13:12
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On CentOS there is /var/log/secure. This holds the fingerprints of the logins:

 Aug  7 23:12:57 my-server sshd[2584]: Accepted publickey for user from 192.168.1.156 port 58279 ssh2: RSA 32:f1:aa:aa:aa:aa:aa:aa:bb:be:ef:c3:aa:bb:cc:f8

Map these back to the keys and you have the info you need. You can get the key fingerprints by doing:

ssh-keygen -l -f ~/.ssh/*.pub

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