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socket_read> <socket_last_error
[edit] Last updated: Sat, 12 May 2012

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(PHP 4 >= 4.1.0, PHP 5)

socket_listenListens for a connection on a socket


bool socket_listen ( resource $socket [, int $backlog = 0 ] )

After the socket socket has been created using socket_create() and bound to a name with socket_bind(), it may be told to listen for incoming connections on socket.

socket_listen() is applicable only to sockets of type SOCK_STREAM or SOCK_SEQPACKET.



A valid socket resource created with socket_create().


A maximum of backlog incoming connections will be queued for processing. If a connection request arrives with the queue full the client may receive an error with an indication of ECONNREFUSED, or, if the underlying protocol supports retransmission, the request may be ignored so that retries may succeed.


The maximum number passed to the backlog parameter highly depends on the underlying platform. On Linux, it is silently truncated to SOMAXCONN. On win32, if passed SOMAXCONN, the underlying service provider responsible for the socket will set the backlog to a maximum reasonable value. There is no standard provision to find out the actual backlog value on this platform.

Return Values

Returns TRUE on success or FALSE on failure. The error code can be retrieved with socket_last_error(). This code may be passed to socket_strerror() to get a textual explanation of the error.

See Also

add a note add a note User Contributed Notes socket_listen
Karuna Govind (karuna.kgx gmail) 15-Jul-2008 11:10
To change the maximum allowed backlog by your system (*nix machines only), first you need to find the variable for this limit:

sudo sysctl -a | grep somaxconn

On ubuntu boxes, it returns net.core.somaxconn (you need to look for the 'somaxconn' variable, the full name will vary across different systems).

Update this to a large number as follows:

sudo sysctl -w net.core.somaxconn=1024

This will work straight away. no restart required.
lewislp at yahoo dot com 30-Aug-2005 07:13
socket_listen() cannot be used for UDP communications as discussed below.

In addition, the example below discusses UDP connections, which only exist if the application manages them through a state table (the OS does not create a UDP connection upon receiving a datagram).  Having a function named socket_connect() that determines the remote IP and port only confuses the matter by giving the indication of some sort of connection handshake between two hosts.  Rather, socket_connect() only specifies the remote IP and port used by subsequent socket_send() calls.  You can achieve the same effect by skipping socket_connect() altogether and specifying the remote IP and port in socket_sendto() calls.

If you find yourself writing a connection-based protocol on top of UDP, consider using TCP.  If your application requires streaming data of some sort, use TCP to manage connections and control messages, and UDP to handle the streaming data (H.323 is an example of a suite of TCP and UDP protocols working in conjunction).

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