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).
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)
- 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
P.O. Box 704
Yorktown Heights, NY 10598, USA
Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA