How does unix_listener works? [Was: Issue with exim and auth protocol]

[Steffen Kaiser]

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On Thu, 31 Jul 2014, Mildred Ki'Lya wrote:
>>
>> Well, first of all auth-userdb and auth-client are completely
>> different things.
>>
>> exim must connect to auth-client and _not_ auth-userdb.
>>
>> 2nd: If the config does not enlist auth-client, look at the full config:
>>
>> doveconf -a
>>
>> There you see all effective settings. hence, I guess you need to
>> replicate the setting from your running server into your local.conf in
>> order to get exim access permissions.
>
> Thank you.
>
> What I don't understand is how unix_listener works and how to specify
> independently the socket file used and the protocol spoken on the socket.
>
> For example, to get postfix to work (I was using postfix before I used
> exim), we configure the auth service this way:
>
>  service auth {
>    unix_listener /var/spool/postfix/private/auth { ... }
>  }
>
> What I deduced from this is that the unix_listener command took a file
> path as argument and the permissions inside the {} block.
>
> Now, when I look at the configuration for auth-userdb and auth-client, I
> see:
>
>  service auth {
>    unix_listener auth-client {... }
>    unix_listener auth-userdb { ... }
>  }
>
> Using the rule deduced above, I see two sockets being declared.
> auth-client is a path relative to /var/run/dovecot, and auth-userdb is
> also a path in /var/run/dovecot. I see no difference between the two,
> except the file path. I deduce then that those two sockets respond to
> the same protocol provided by the service auth.
>
> Obviously, I am wrong.
>
> Then, how does the auth service knows which protocol to speak on
> /var/run/dovecot/auth-userdb, /var/run/dovecot/auth-client and
> /var/spool/postfix/private/auth? This is not specified in the
> configuration (even doveconf -a).

See http://wiki2.dovecot.org/Services#auth

"With UNIX listeners the client type is selected based on the filename 
after the last "-" in the filename. For example "anything-userdb" is of 
"userdb" type. The default type is "client" for inet insteners and 
unrecognized UNIX listeners. "

- -- 
Steffen Kaiser
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