SCACHE(8) System Manager's Manual SCACHE(8)
NAME
scache - Postfix shared connection cache server
SYNOPSIS
scache [generic Postfix daemon options]
DESCRIPTION
The scache(8) server maintains a shared multi-connection cache. This information can be used by, for example,
Postfix 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 end‐
points specify (transport, IP address, port). An SMTP connection may be saved after a successful mail trans‐
action.
In the general case, one logical destination may refer to zero or more physical endpoints, one physical end‐
point may be referenced by zero or more logical destinations, and one endpoint may refer to zero or more con‐
nections.
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
that information.
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.
find_endp endpoint
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.
find_dest destination
Look up cached destination properties, cached endpoint properties, and a cached file descriptor for the
specified logical destination.
SECURITY
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 privilege.
The scache(8) server is not a trusted process. It must not be used to store information that is security sen‐
sitive.
DIAGNOSTICS
Problems and transactions are logged to syslogd(8).
connection_cache_ttl_limit (2s)
The maximal time-to-live value that the scache(8) connection cache server allows.
connection_cache_status_update_time (600s)
How frequently the scache(8) server logs usage statistics with connection cache hit and miss rates for
logical destinations and for physical endpoints.
MISCELLANEOUS CONTROLS
config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and master.cf configuration files.
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.
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.
syslog_facility (mail)
The syslog facility of Postfix logging.
syslog_name (see 'postconf -d' output)
The mail system name that is prepended to the process name in syslog records, so that "smtpd" becomes,
for example, "postfix/smtpd".
SEE ALSO
smtp(8), SMTP client
postconf(5), configuration parameters
master(8), process manager
syslogd(8), system logging
README FILES
Use "postconf readme_directory" or "postconf html_directory" to locate this information.
CONNECTION_CACHE_README, Postfix connection cache
LICENSE
The Secure Mailer license must be distributed with this software.
HISTORY
This service was introduced with Postfix version 2.2.
AUTHOR(S)
Wietse Venema
IBM T.J. Watson Research
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