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diff --git a/man2/listen.2 b/man2/listen.2 new file mode 100644 index 0000000..9512366 --- /dev/null +++ b/man2/listen.2 @@ -0,0 +1,155 @@ +.\" Copyright (c) 1983, 1991 The Regents of the University of California. +.\" and Copyright (C) 2007, Michael Kerrisk <mtk.manpages@gmail.com> +.\" All rights reserved. +.\" +.\" SPDX-License-Identifier: BSD-4-Clause-UC +.\" +.\" $Id: listen.2,v 1.6 1999/05/18 14:10:32 freitag Exp $ +.\" +.\" Modified Fri Jul 23 22:07:54 1993 by Rik Faith <faith@cs.unc.edu> +.\" Modified 950727 by aeb, following a suggestion by Urs Thuermann +.\" <urs@isnogud.escape.de> +.\" Modified Tue Oct 22 08:11:14 EDT 1996 by Eric S. Raymond <esr@thyrsus.com> +.\" Modified 1998 by Andi Kleen +.\" Modified 11 May 2001 by Sam Varshavchik <mrsam@courier-mta.com> +.\" +.\" +.TH listen 2 2023-03-30 "Linux man-pages 6.05.01" +.SH NAME +listen \- listen for connections on a socket +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B #include <sys/socket.h> +.PP +.BI "int listen(int " sockfd ", int " backlog ); +.fi +.SH DESCRIPTION +.BR listen () +marks the socket referred to by +.I sockfd +as a passive socket, that is, as a socket that will +be used to accept incoming connection requests using +.BR accept (2). +.PP +The +.I sockfd +argument is a file descriptor that refers to a socket of type +.B SOCK_STREAM +or +.BR SOCK_SEQPACKET . +.PP +The +.I backlog +argument defines the maximum length +to which the queue of pending connections for +.I sockfd +may grow. +If a connection request arrives when the queue is full, the client +may receive an error with an indication of +.B ECONNREFUSED +or, if the underlying protocol supports retransmission, the request may be +ignored so that a later reattempt at connection succeeds. +.SH RETURN VALUE +On success, zero is returned. +On error, \-1 is returned, and +.I errno +is set to indicate the error. +.SH ERRORS +.TP +.B EADDRINUSE +Another socket is already listening on the same port. +.TP +.B EADDRINUSE +(Internet domain sockets) +The socket referred to by +.I sockfd +had not previously been bound to an address and, +upon attempting to bind it to an ephemeral port, +it was determined that all port numbers in the ephemeral port range +are currently in use. +See the discussion of +.I /proc/sys/net/ipv4/ip_local_port_range +in +.BR ip (7). +.TP +.B EBADF +The argument +.I sockfd +is not a valid file descriptor. +.TP +.B ENOTSOCK +The file descriptor +.I sockfd +does not refer to a socket. +.TP +.B EOPNOTSUPP +The socket is not of a type that supports the +.BR listen () +operation. +.SH STANDARDS +POSIX.1-2008. +.SH HISTORY +POSIX.1-2001, 4.4BSD +(first appeared in 4.2BSD). +.SH NOTES +To accept connections, the following steps are performed: +.RS 4 +.IP (1) 5 +A socket is created with +.BR socket (2). +.IP (2) +The socket is bound to a local address using +.BR bind (2), +so that other sockets may be +.BR connect (2)ed +to it. +.IP (3) +A willingness to accept incoming connections and a queue limit for incoming +connections are specified with +.BR listen (). +.IP (4) +Connections are accepted with +.BR accept (2). +.RE +.PP +The behavior of the +.I backlog +argument on TCP sockets changed with Linux 2.2. +Now it specifies the queue length for +.I 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 +.IR /proc/sys/net/ipv4/tcp_max_syn_backlog . +When syncookies are enabled there is no logical maximum +length and this setting is ignored. +See +.BR tcp (7) +for more information. +.PP +If the +.I backlog +argument is greater than the value in +.IR /proc/sys/net/core/somaxconn , +then it is silently capped to that value. +Since Linux 5.4, the default in this file is 4096; +in earlier kernels, the default value is 128. +Before Linux 2.4.25, this limit was a hard coded value, +.BR SOMAXCONN , +with the value 128. +.\" The following is now rather historic information (MTK, Jun 05) +.\" Don't rely on this value in portable applications since BSD +.\" (and some BSD-derived systems) limit the backlog to 5. +.SH EXAMPLES +See +.BR bind (2). +.SH SEE ALSO +.BR accept (2), +.BR bind (2), +.BR connect (2), +.BR socket (2), +.BR socket (7) |