listen

Sets the address and port for the socket on which the server will accept connections. It is possible to specify just the port. The address can also be a hostname, for example:

listen 127.0.0.1:12345;
listen *:12345;
listen 12345;     # same as *:12345
listen localhost:12345;

IPv6 addresses are specified in square brackets:

listen [::1]:12345;
listen [::]:12345;

UNIX-domain sockets are specified with the “unix:” prefix:

listen unix:/var/run/nginx.sock;

The ssl parameter allows specifying that all connections accepted on this port should work in SSL mode.

The udp parameter configures a listening socket for working with datagrams (1.9.13).

The proxy_protocol parameter (1.11.4) allows specifying that all connections accepted on this port should use the PROXY protocol.

The listen directive can have several additional parameters specific to socket-related system calls.

backlog=number

sets the backlog parameter in the listen() call that limits the maximum length for the queue of pending connections (1.9.2). By default, backlog is set to -1 on FreeBSD, DragonFly BSD, and Mac OS X, and to 511 on other platforms.

bind

this parameter instructs to make a separate bind() call for a given address:port pair. The fact is that if there are several listen directives with the same port but different addresses, and one of the listen directives listens on all addresses for the given port (*:port), nginx will bind() only to *:port. It should be noted that the getsockname() system call will be made in this case to determine the address that accepted the connection. If the ipv6only or so_keepalive parameters are used then for a given address:port pair a separate bind() call will always be made.

ipv6only=on|off

this parameter determines (via the IPV6_V6ONLY socket option) whether an IPv6 socket listening on a wildcard address [::] will accept only IPv6 connections or both IPv6 and IPv4 connections. This parameter is turned on by default. It can only be set once on start.

reuseport

this parameter (1.9.1) instructs to create an individual listening socket for each worker process (using the SO_REUSEPORT socket option), allowing a kernel to distribute incoming connections between worker processes. This currently works only on Linux 3.9+ and DragonFly BSD.

Inappropriate use of this option may have its security implications.

so_keepalive=on|off|[keepidle]:[keepintvl]:[keepcnt]

this parameter configures the “TCP keepalive” behavior for the listening socket. If this parameter is omitted then the operating system’s settings will be in effect for the socket. If it is set to the value “on”, the SO_KEEPALIVE option is turned on for the socket. If it is set to the value “off”, the SO_KEEPALIVE option is turned off for the socket. Some operating systems support setting of TCP keepalive parameters on a per-socket basis using the TCP_KEEPIDLE, TCP_KEEPINTVL, and TCP_KEEPCNT socket options. On such systems (currently, Linux 2.4+, NetBSD 5+, and FreeBSD 9.0-STABLE), they can be configured using the keepidle, keepintvl, and keepcnt parameters. One or two parameters may be omitted, in which case the system default setting for the corresponding socket option will be in effect. For example,

so_keepalive=30m::10

will set the idle timeout (TCP_KEEPIDLE) to 30 minutes, leave the probe interval (TCP_KEEPINTVL) at its system default, and set the probes count (TCP_KEEPCNT) to 10 probes.

Different servers must listen on different address:port pairs.