Updated: 2022/Sep/29
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PROXYMAP(8) System Manager's Manual PROXYMAP(8)
NAME
proxymap - 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) or postlogd(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.
Available in Postfix 3.3 and later:
service_name (read-only)
The master.cf service name of a Postfix daemon process.
SEE ALSO
postconf(5), configuration parameters
master(5), generic daemon options
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
PROXYMAP(8)