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listen(2) System Calls Manual listen(2) NAME listen - Listens for socket connections and limits the backlog of in- coming connections SYNOPSIS #include <sys/socket.h> int listen ( int socket, int backlog ); STANDARDS Interfaces documented on this reference page conform to industry stan- dards as follows: listen(): XPG4-UNIX Refer to the standards(5) reference page for more information about in- dustry 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 connec- tions, 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 spec- ify is indicated by the SOMAXCONN value in the sys/socket.h header file. 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 indi- cate the error. ERRORS If the listen() function fails, errno may be set to one of the follow- ing values: 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. 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)