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I'm a novice at network things. I enabled remote-login on my home mac (OS 10.12.5) so I could git between home and office. To make it work, I had to tell the wifi to fix my Mac's IP and to redirect Port 22 to it. Works fine. My log file, however, has thousands of messages (one every few seconds) of the form:

com.apple.xpc.launchd[1] (com.openssh.sshd._hex_[_int_]): Service exited with abnormal code: 255

Nothing in the log explicitly mentions a refused authentication, and I don't seem to have an auth.log or secure.log file (other posts suggested to look in there).

Any idea what's going on here?

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    Try reading this – Paradoxis Jul 29 '17 at 11:03
  • Do you have Little Snitch or a similar firewall program installed? – user2707001 Jul 29 '17 at 11:23
  • @user2707001 : I have the OSX firewall on, but nothing else. I didn't post this because I assumed the Mac built-ins should play well together. Will edit question if you think it might be relevant. – Ryan Tierney Jul 29 '17 at 11:45
  • @Paradoxis: Thanks for the link. It's a bit above my level, but I'm not (purposely) running anything on the home Mac that invokes ssh commands. Home mac is the Git 'origin' and 'remote' is office. Will Git automatically try to contact remotes? Also: remote currently shut down, and likewise has (to my knowledge) no scripts trying to contact origin. – Ryan Tierney Jul 29 '17 at 11:49
  • Could you check from office Mac: ssh home_mac pwd and if it gives an error, add this information to your OQ? – dan Jul 29 '17 at 16:00
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That's the log entry performed when sshd denies a connection. You're probably seeing unauthorised users trying to brute force their way in by trying common usernames and passwords. There used to also be a log entry directly from sshd itself telling you the IP address and username attempted, but Apple has decided to labotomize standard UNIX logging from sshd.

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