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listen(7) [centos man page]

LISTEN(7)						  PostgreSQL 9.2.7 Documentation						 LISTEN(7)

NAME
LISTEN - listen for a notification SYNOPSIS
LISTEN channel DESCRIPTION
LISTEN registers the current session as a listener on the notification channel named channel. If the current session is already registered as a listener for this notification channel, nothing is done. Whenever the command NOTIFY channel is invoked, either by this session or another one connected to the same database, all the sessions currently listening on that notification channel are notified, and each will in turn notify its connected client application. A session can be unregistered for a given notification channel with the UNLISTEN command. A session's listen registrations are automatically cleared when the session ends. The method a client application must use to detect notification events depends on which PostgreSQL application programming interface it uses. With the libpq library, the application issues LISTEN as an ordinary SQL command, and then must periodically call the function PQnotifies to find out whether any notification events have been received. Other interfaces such as libpgtcl provide higher-level methods for handling notify events; indeed, with libpgtcl the application programmer should not even issue LISTEN or UNLISTEN directly. See the documentation for the interface you are using for more details. NOTIFY(7) contains a more extensive discussion of the use of LISTEN and NOTIFY. PARAMETERS
channel Name of a notification channel (any identifier). NOTES
LISTEN takes effect at transaction commit. If LISTEN or UNLISTEN is executed within a transaction that later rolls back, the set of notification channels being listened to is unchanged. A transaction that has executed LISTEN cannot be prepared for two-phase commit. EXAMPLES
Configure and execute a listen/notify sequence from psql: LISTEN virtual; NOTIFY virtual; Asynchronous notification "virtual" received from server process with PID 8448. COMPATIBILITY
There is no LISTEN statement in the SQL standard. SEE ALSO
NOTIFY(7), UNLISTEN(7) PostgreSQL 9.2.7 2014-02-17 LISTEN(7)

Check Out this Related Man Page

UPSD.CONF(5)							    NUT Manual							      UPSD.CONF(5)

NAME
upsd.conf - Configuration for Network UPS Tools upsd DESCRIPTION
upsd uses this file to control access to the server and set some other miscellaneous configuration values. This file contains details on access controls, so keep it secure. Ideally, only the upsd process should be able to read it. CONFIGURATION DIRECTIVES
"MAXAGE seconds" upsd usually allows a driver to stop responding for up to 15 seconds before declaring the data "stale". If your driver takes a very long time to process updates but is otherwise operational, you can use MAXAGE to make upsd wait longer. Most users should leave this at the default value. "STATEPATH path" Tell upsd to look for the driver state sockets in path rather than the default that was compiled into the program. "LISTEN interface port" Bind a listening port to the interface specified by its Internet address. This may be useful on hosts with multiple interfaces. You should not rely exclusively on this for security, as it can be subverted on many systems. Listen on TCP port port instead of the default value which was compiled into the code. This overrides any value you may have set with configure --with-port. If you don't change it with configure or this value, upsd will listen on port 3493 for this interface. Multiple LISTEN addresses may be specified. The default is to bind to 127.0.0.1 if no LISTEN addresses are specified (and ::1 if IPv6 support is compiled in). LISTEN 127.0.0.1 LISTEN 192.168.50.1 LISTEN ::1 LISTEN 2001:0db8:1234:08d3:1319:8a2e:0370:7344 This parameter will only be read at startup. You'll need to restart (rather than reload) upsd to apply any changes made here. "MAXCONN connections" This defaults to maximum number allowed on your system. Each UPS, each LISTEN address and each client count as one connection. If the server runs out of connections, it will no longer accept new incoming client connections. Only set this if you know exactly what you're doing. "CERTFILE certificate file" When compiled with SSL support, you can enter the certificate file here. The certificates must be in PEM format and must be sorted starting with the subject's certificate (server certificate), followed by intermediate CA certificates (if applicable_ and the highest level (root) CA. It should end with the server key. See docs/security.txt or the Security chapter of NUT user manual for more information on the SSL support in NUT. SEE ALSO
upsd(8), nutupsdrv(8), upsd.users(5) INTERNET RESOURCES
The NUT (Network UPS Tools) home page: http://www.networkupstools.org/ Network UPS Tools 05/21/2012 UPSD.CONF(5)

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