scache - Postfix shared connection cache server
scache [generic Postfix daemon options]
The scache(8) server maintains a shared multi-connection
cache. This information can be used by, for example, Post-
fix SMTP clients or other Postfix delivery agents.
The connection cache is organized into logical destination
names, physical endpoint names, and connections.
As a specific example, logical SMTP destinations specify
(transport, domain, port), and physical SMTP endpoints
specify (transport, IP address, port). An SMTP connection
may be saved after a successful mail transaction.
In the general case, one logical destination may refer to
zero or more physical endpoints, one physical endpoint may
be referenced by zero or more logical destinations, and
one endpoint may refer to zero or more connections.
The exact syntax of a logical destination or endpoint name
is application dependent; the scache(8) server does not
care. A connection is stored as a file descriptor
together with application-dependent information that is
needed to re-activate a connection object. Again, the
scache(8) server is completely unaware of the details of
All information is stored with a finite time to live
(ttl). The connection cache daemon terminates when no
client is connected for max_idle time units.
This server implements the following requests:
save_endp ttl endpoint endpoint_properties file_descriptor
Save the specified file descriptor and connection
property data under the specified endpoint name.
The endpoint properties are used by the client to
re-activate a passivated connection object.
Look up cached properties and a cached file
descriptor for the specified endpoint.
save_dest ttl destination destination_properties endpoint
Save the binding between a logical destination and
an endpoint under the destination name, together
with destination specific connection properties.
The destination properties are used by the client
to re-activate a passivated connection object.
Look up cached destination properties, cached end-
point properties, and a cached file descriptor for
the specified logical destination.
The scache(8) server is not security-sensitive. It does
not talk to the network, and it does not talk to local
users. The scache(8) server can run chrooted at fixed low
The scache(8) server is not a trusted process. It must not
be used to store information that is security sensitive.
Problems and transactions are logged to syslogd(8).
The session cache cannot be shared among multiple
When a connection expires from the cache, it is closed
without the appropriate protocol specific handshake.
Changes to main.cf are picked up automatically as
scache(8) processes run for only a limited amount of time.
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.
The maximal time-to-live value that the scache(8)
connection cache server allows.
How frequently the scache(8) server logs usage sta-
tistics with connection cache hit and miss rates
for logical destinations and for physical end-
config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and
master.cf configuration files.
How much time a Postfix daemon process may take to
handle a request before it is terminated by a
built-in watchdog timer.
The time limit for sending or receiving information
over an internal communication channel.
The maximum amount of time that an idle Postfix
daemon process waits for the next service request
The process ID of a Postfix command or daemon
The process name of a Postfix command or daemon
The syslog facility of Postfix logging.
The mail system name that is prepended to the
process name in syslog records, so that "smtpd"
becomes, for example, "postfix/smtpd".
smtp(8), SMTP client
postconf(5), configuration parameters
master(8), process manager
syslogd(8), system logging
CONNECTION_CACHE_README, Postfix connection cache
The Secure Mailer license must be distributed with this
This service was introduced with Postfix version 2.2.
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA