PROXYMAP(8) 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:
o To overcome chroot restrictions. For example, a
chrooted SMTP server needs access to the system
passwd file in order to reject mail for non-exis-
tent 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
o 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 connec-
tions" 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.
o To provide single-updater functionality for lookup
tables that do not reliably support multiple writ-
ers (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 map-
type 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.
The request completion status is one of OK, RETRY, NOKEY
(lookup failed because the key was not found), BAD (mal-
formed 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 mas-
ter(8) server. Each server can handle multiple simultane-
ous 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 user or group IDs, mailbox file/directory names or
external commands.
In Postfix version 2.2 and later, the proxymap client rec-
ognizes 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-sen-
sitive processes.
Postfix-writable data files should be stored under a dedi-
cated 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 direc-
tory 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 imple-
mented by a real DBMS.
CONFIGURATION PARAMETERS
On busy mail systems a long time may pass before prox-
ymap(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 termi-
nating 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.
SEE ALSO
postconf(5), configuration parameters
master(5), generic daemon options
README FILES
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
PROXYMAP(8)