Postgresql cannot peer authenticate using usermap (provided user name (^dbuser^) and authenticated user name (^sysuser^) do not match)

Question

I am trying to peer authenticate some users using usermap. What I am trying to do is to map user mailreader as you can see:

postgres=# \du
 List of roles
 Role name | Attributes | Member of 
------------+------------------------------------------------+-----------
 mailreader | | {}
 postgres | Superuser, Create role, Create DB, Replication | {}

Into system's user root,dovecot,postfix. Therefore I edited my pg_ident.conf and put the following content:

mailmap dovecot mailreader
mailmap postfix mailreader
mailmap root mailreader

I also edited the pg_hba.conf and appended with the following content:

local mail all peer map=mailmap

When I try to connect via sudo psql -U mailreader -d mail command I get:

psql: FATAL: Peer authentication failed for user "mailreader"

error.

I also tried the following configuration:

local mail all ident map=mailmap

Without any progress.

May I have some help?

Edit 1

The logs regarding the error is:

2017年06月27日 19:10:10 UTC [1188-1] mailreader@mail LOG: provided user name (mailreader) and authenticated user name (root) do not match
2017年06月27日 19:10:10 UTC [1188-2] mailreader@mail FATAL: Peer authentication failed for user "mailreader"
2017年06月27日 19:10:10 UTC [1188-3] mailreader@mail DETAIL: Connection matched pg_hba.conf line 90: "local all all peer"

• jjanes: Did you restart the server, or reload the configuration files, after changing them?
• jjanes: Look in the postgres server log file for more detailed error reporting. The message returned to the client is intentionally vague, to avoid leaking information to an attacker.
• Dimitrios Desyllas: @jjanes Yes I did that

Answer 1

In the end I had to comment the line:

local all all peer

Or to put it below the following line:

local mail all ident map=mailmap

• Ale: Had the same problem. Basically, pg_hba.conf entries are taken in the order they are in the file, the first (not the better) match is used!