Ha, I&#x27;ve literally just finished debugging an SSH connection failure which turned-out to be caused by ACLs!<p>An inappropriately-recursive setfacl added additional read &#x2F; exec rights to the key files in a user&#x27;s .ssh directory, which caused SSH to bail-out without establishing a connection.  Subtle to find, it was only the &quot;+&quot; suffixed on the ls -al output that gave the clue...<p>ACLs are very powerful for solving specific problems but as the blog-post points-out they can have all sorts of unexpected side-effects.