Updated: 2022/Sep/29
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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 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 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 sensitive.
DIAGNOSTICS
Problems and transactions are logged to syslogd(8) or postlogd(8).
BUGS
The session cache cannot be shared among multiple machines.
When a connection expires from the cache, it is closed without the
appropriate protocol specific handshake.
CONFIGURATION PARAMETERS
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.
RESOURCE CONTROLS
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)
A prefix that is prepended to the process name in syslog
records, so that, for example, "smtpd" becomes "prefix/smtpd".
Available in Postfix 3.3 and later:
service_name (read-only)
The master.cf service name of a Postfix daemon process.
SEE ALSO
smtp(8), SMTP client
postconf(5), configuration parameters
master(8), process manager
postlogd(8), Postfix logging
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
P.O. Box 704
Yorktown Heights, NY 10598, USA
Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA
SCACHE(8)