| Linux / Unix Command: accept |
NAME
accept - accept a connection on a socketSYNOPSIS
#include <sys/types.h>#include <sys/socket.h>
int accept(int s, struct sockaddr *addr, socklen_t *addrlen);
DESCRIPTION
The accept function is used with connection-based socket types (SOCK_STREAM, SOCK_SEQPACKET and SOCK_RDM). It extracts the first connection request on the queue of pending connections, creates a new connected socket with mostly the same properties as s, and allocates a new file descriptor for the socket, which is returned. The newly created socket is no longer in the listening state. The original socket s is unaffected by this call. Note that any per file descriptor flags (everything that can be set with the F_SETFL fcntl, like non blocking or async state) are not inherited across an accept.
The argument s is a socket that has been created with socket(2), bound to a local address with bind(2), and is listening for connections after a listen(2).
The argument addr is a pointer to a sockaddr structure. This structure is filled in with the address of the connecting entity, as known to the communications layer. The exact format of the address passed in the addr parameter is determined by the socket's family (see socket(2) and the respective protocol man pages). The addrlen argument is a value-result parameter: it should initially contain the size of the structure pointed to by addr; on return it will contain the actual length (in bytes) of the address returned. When addr is NULL nothing is filled in.
If no pending connections are present on the queue, and the socket is not marked as non-blocking, accept blocks the caller until a connection is present. If the socket is marked non-blocking and no pending connections are present on the queue, accept returns EAGAIN.
In order to be notified of incoming connections on a socket, you can use select(2) or poll(2). A readable event will be delivered when a new connection is attempted and you may then call accept to get a socket for that connection. Alternatively, you can set the socket to deliver SIGIO when activity occurs on a socket; see socket(7) for details.
For certain protocols which require an explicit confirmation, such as DECNet, accept can be thought of as merely dequeuing the next connection request and not implying confirmation. Confirmation can be implied by a normal read or write on the new file descriptor, and rejection can be implied by closing the new socket. Currently only DECNet has these semantics on Linux.
SEE ALSO
bind(2), connect(2), listen(2), select(2), socket(2)
Important: Use the man command (% man) to see how a command is used on your particular computer.
