proxymap(8) Postfix lookup table proxy server

SYNOPSIS

proxymap [generic Postfix daemon options]

DESCRIPTION

The proxymap(8) server provides read-only or read-write table lookup service to Postfix processes. These services are implemented with distinct service names: proxymap and proxywrite, respectively. The purpose of these services is:
  • To overcome chroot restrictions. For example, a chrooted SMTP server needs access to the system passwd file in order to reject mail for non-existent local addresses, but it is not practical to maintain a copy of the passwd file in the chroot jail. The solution: 

    local_recipient_maps =
    proxy:unix:passwd.byname $alias_maps
  • To consolidate the number of open lookup tables by sharing one open table among multiple processes. For example, making mysql connections from every Postfix daemon process results in "too many connections" errors. The solution: 

    virtual_alias_maps =
    proxy:mysql:/etc/postfix/virtual_alias.cf

    The total number of connections is limited by the number of proxymap server processes.

  • To provide single-updater functionality for lookup tables that do not reliably support multiple writers (i.e. all file-based tables).

The proxymap(8) server implements the following requests:

open maptype:mapname flags
Open the table with type maptype and name mapname, as controlled by flags. The reply includes the maptype dependent flags (to distinguish a fixed string table from a regular expression table).
lookup maptype:mapname flags key
Look up the data stored under the requested key. The reply is the request completion status code and the lookup result value. The maptype:mapname and flags are the same as with the open request.
update maptype:mapname flags key value
Update the data stored under the requested key. The reply is the request completion status code. The maptype:mapname and flags are the same as with the open request.

To implement single-updater maps, specify a process limit of 1 in the master.cf file entry for the proxywrite service.

This request is supported in Postfix 2.5 and later.

delete maptype:mapname flags key
Delete the data stored under the requested key. The reply is the request completion status code. The maptype:mapname and flags are the same as with the open request.

This request is supported in Postfix 2.5 and later.

sequence maptype:mapname flags function
Iterate over the specified database. The function is one of DICT_SEQ_FUN_FIRST or DICT_SEQ_FUN_NEXT. The reply is the request completion status code and a lookup key and result value, if found.

This request is supported in Postfix 2.9 and later.

The request completion status is one of OK, RETRY, NOKEY (lookup failed because the key was not found), BAD (malformed request) or DENY (the table is not approved for proxy read or update access).

There is no close command, nor are tables implicitly closed when a client disconnects. The purpose is to share tables among multiple client processes.

SERVER PROCESS MANAGEMENT



proxymap(8) servers run under control by the Postfix
master(8)
server.  Each server can handle multiple simultaneous connections.
When all servers are busy while a client connects, the master(8)
creates a new proxymap(8) server process, provided that the
process limit is not exceeded.
Each server terminates after serving at least $max_use clients
or after $max_idle seconds of idle time.





SECURITY





The proxymap(8) server opens only tables that are
approved via the proxy_read_maps or proxy_write_maps
configuration parameters, does not talk to
users, and can run at fixed low privilege, chrooted or not.
However, running the proxymap server chrooted severely limits
usability, because it can open only chrooted tables.


The proxymap(8) server is not a trusted daemon process, and must
not be used to look up sensitive information such as UNIX user or
group IDs, mailbox file/directory names or external commands.


In Postfix version 2.2 and later, the proxymap client recognizes
requests to access a table for security-sensitive purposes,
and opens the table directly. This allows the same main.cf
setting to be used by sensitive and non-sensitive processes.


Postfix-writable data files should be stored under a dedicated
directory that is writable only by the Postfix mail system,
such as the Postfix-owned data_directory.


In particular, Postfix-writable files should never exist
in root-owned directories. That would open up a particular
type of security hole where ownership of a file or directory
does not match the provider of its content.





DIAGNOSTICS

Problems and transactions are logged to syslogd(8).





BUGS

The proxymap(8) server provides service to multiple clients,
and must therefore not be used for tables that have high-latency
lookups.


The proxymap(8) read-write service does not explicitly
close lookup tables (even if it did, this could not be relied on,
because the process may be terminated between table updates).
The read-write service should therefore not be used with tables that
leave persistent storage in an inconsistent state between
updates (for example, CDB). Tables that support "sync on
update" should be safe (for example, Berkeley DB) as should
tables that are implemented by a real DBMS.





CONFIGURATION PARAMETERS





On busy mail systems a long time may pass before
proxymap(8) relevant
changes to main.cf are picked up. Use the command
"postfix reload" to speed up a change.


The text below provides only a parameter summary. See
postconf(5) for more details including examples.



config_directory (see 'postconf -d' output)

The default location of the Postfix main.cf and master.cf
configuration files.

data_directory (see 'postconf -d' output)

The directory with Postfix-writable data files (for example:
caches, pseudo-random numbers).

daemon_timeout (18000s)

How much time a Postfix daemon process may take to handle a
request before it is terminated by a built-in watchdog timer.

ipc_timeout (3600s)

The time limit for sending or receiving information over an internal
communication channel.

max_idle (100s)

The maximum amount of time that an idle Postfix daemon process waits
for an incoming connection before terminating voluntarily.

max_use (100)

The maximal number of incoming connections that a Postfix daemon
process will service before terminating voluntarily.

process_id (read-only)

The process ID of a Postfix command or daemon process.

process_name (read-only)

The process name of a Postfix command or daemon process.

proxy_read_maps (see 'postconf -d' output)

The lookup tables that the proxymap(8) server is allowed to
access for the read-only service.




Available in Postfix 2.5 and later:



data_directory (see 'postconf -d' output)

The directory with Postfix-writable data files (for example:
caches, pseudo-random numbers).

proxy_write_maps (see 'postconf -d' output)

The lookup tables that the proxymap(8) server is allowed to
access for the read-write service.








README FILES





Use "postconf readme_directory" or
"postconf html_directory" to locate this information.

DATABASE_README, Postfix lookup table overview







LICENSE





The Secure Mailer license must be distributed with this software.





HISTORY

The proxymap service was introduced with Postfix 2.0.





AUTHOR(S)




Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA





      

    



  









  

  


    

      
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