Section: Maintenance Commands (8)
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Postfix lookup table proxy server
proxymap [generic Postfix daemon options]
The proxymap(8) server provides read-only table
lookup service to Postfix processes. The purpose
of the service 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:
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:
The total number of connections is limited by the number of
proxymap server processes.
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
- lookup maptype:mapname flags key
Look up the data stored under the requested key.
The reply is the request completion status code (below) and
the lookup result value.
The maptype:mapname and flags are the same
as with the open request.
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
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.
The proxymap(8) server opens only tables that are approved via the
proxy_read_maps configuration parameter, 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 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.
Problems and transactions are logged to syslogd(8).
The proxymap(8) server provides service to multiple clients,
and must therefore not be used for tables that have high-latency
On busy mail systems a long time may pass before
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
- 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
- max_idle (100s)
The maximum amount of time that an idle Postfix daemon process
waits for the next service request before exiting.
- max_use (100)
The maximal number of connection requests before a Postfix daemon
- 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.
postconf(5), configuration parameters
master(5), generic daemon options
Use "postconf readme_directory" or
"postconf html_directory" to locate this information.
DATABASE_README, Postfix lookup table overview
The Secure Mailer license must be distributed with this software.
The proxymap service was introduced with Postfix 2.0.
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
- SERVER PROCESS MANAGEMENT
- CONFIGURATION PARAMETERS
- SEE ALSO
- README FILES
linux.jgfs.net manual pages