listen(2) [osf1 man page]
listen(2) System Calls Manual listen(2) NAME
listen - Listens for socket connections and limits the backlog of incoming connections SYNOPSIS
#include <sys/socket.h> int listen ( int socket, int backlog ); STANDARDS
Interfaces documented on this reference page conform to industry standards as follows: listen(): XNS5.0 Refer to the standards(5) reference page for more information about industry standards and associated tags. PARAMETERS
Specifies the unique name for the socket. Specifies the maximum number of outstanding connection requests. DESCRIPTION
The listen() function identifies the socket that receives the connections, marks the socket as accepting connections, and limits the number (backlog) of outstanding connection requests in the system queue. The maximum queue length (backlog) that the listen() function can specify is indicated by the SOMAXCONN value in the sys/socket.h header file. The socket in use may require that the process have appropriate privileges to use the listen() function. RETURN VALUES
Upon successful completion, the listen() function returns a value of 0 (zero). Otherwise, a value of -1 is returned and errno is set to indicate the error. ERRORS
If the listen() function fails, errno may be set to one of the following values: The requested address is protected and the current process does not have permission to access it. The socket parameter is not valid. The socket is not bound to a local address, and the protocol does not support listening on an unbound socket. The socket is already connected; or the socket is shut down. Insufficient resources are available in the system to complete the call. The socket parameter refers to a file, not a socket. The referenced socket is not a type that supports the listen() function. RELATED INFORMATION
Functions: accept(2), connect(2), socket(2) Standards: standards(5) delim off listen(2)
Check Out this Related Man Page
LISTEN(2) Linux Programmer's Manual LISTEN(2) NAME
listen - listen for connections on a socket SYNOPSIS
#include <sys/socket.h> int listen(int s, int backlog); DESCRIPTION
To accept connections, a socket is first created with socket(2), a willingness to accept incoming connections and a queue limit for incom- ing connections are specified with listen, and then the connections are accepted with accept(2). The listen call applies only to sockets of type SOCK_STREAM or SOCK_SEQPACKET. The backlog parameter defines the maximum length the queue of pending connections may grow to. 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 succeed. NOTES
The behaviour of the backlog parameter on TCP sockets changed with Linux 2.2. Now it specifies the queue length for completely established sockets waiting to be accepted, instead of the number of incomplete connection requests. The maximum length of the queue for incomplete sockets can be set using the tcp_max_syn_backlog sysctl. When syncookies are enabled there is no logical maximum length and this sysctl setting is ignored. See tcp(7) for more information. RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately. ERRORS
EADDRINUSE Another socket is already listening on the same port. EBADF The argument s is not a valid descriptor. ENOTSOCK The argument s is not a socket. EOPNOTSUPP The socket is not of a type that supports the listen operation. CONFORMING TO
Single Unix, 4.4BSD, POSIX 1003.1g draft. The listen function call first appeared in 4.2BSD. BUGS
If the socket is of type AF_INET, and the backlog argument is greater than the constant SOMAXCONN (128 in Linux 2.0 & 2.2), it is silently truncated to SOMAXCONN. Don't rely on this value in portable applications since BSD (and some BSD-derived systems) limit the backlog to 5. SEE ALSO
accept(2), connect(2), socket(2) BSD Man Page 1993-07-23 LISTEN(2)