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ACCEPT(2) BSD System Calls Manual ACCEPT(2) NAME accept -- accept a connection on a socket LIBRARY Standard C Library (libc, -lc) SYNOPSIS #include <sys/types.h> #include <sys/socket.h> int accept(int s, struct sockaddr * restrict addr, socklen_t * restrict addrlen); DESCRIPTION The argument s is a socket that has been created with socket(2), bound to an address with bind(2), and is listening for connections after a listen(2). The accept() system call extracts the first connection re- quest on the queue of pending connections, creates a new socket, and al- locates a new file descriptor for the socket which inherits the state of the O_NONBLOCK property from the original socket s. If no pending connections are present on the queue, and the original socket is not marked as non-blocking, accept() blocks the caller until a connection is present. If the original socket is marked non-blocking and no pending connections are present on the queue, accept() returns an er- ror as described below. The accepted socket may not be used to accept more connections. The original socket s remains open. The argument addr is a result argument that is filled-in with the address of the connecting entity, as known to the communications layer. The ex- act format of the addr argument is determined by the domain in which the communication is occurring. A null pointer may be specified for addr if the address information is not desired; in this case, addrlen is not used and should also be null. Otherwise, the addrlen argument is a value-re- sult argument; it should initially contain the amount of space pointed to by addr; on return it will contain the actual length (in bytes) of the address returned. This call is used with connection-based socket types, currently with SOCK_STREAM. It is possible to select(2) a socket for the purposes of doing an accept() by selecting it for read. For certain protocols which require an explicit confirmation, such as ISO or DATAKIT, accept() can be thought of as merely dequeueing the next con- nection request and not implying confirmation. Confirmation can be im- plied by a normal read or write on the new file descriptor, and rejection can be implied by closing the new socket. For some applications, performance may be enhanced by using an accept_filter(9) to pre-process incoming connections. RETURN VALUES The call returns -1 on error. If it succeeds, it returns a non-negative integer that is a descriptor for the accepted socket. ERRORS The accept() system call will fail if: [EBADF] The descriptor is invalid. [EINTR] The accept() operation was interrupted. [EMFILE] The per-process descriptor table is full. [ENFILE] The system file table is full. [ENOTSOCK] The descriptor references a file, not a socket. [EINVAL] listen(2) has not been called on the socket descrip- tor. [EINVAL] The addrlen argument is negative. [EFAULT] The addr argument is not in a writable part of the user address space. [EWOULDBLOCK] The socket is marked non-blocking and no connections are present to be accepted. [ECONNABORTED] A connection arrived, but it was closed while waiting on the listen queue. SEE ALSO bind(2), connect(2), getpeername(2), listen(2), select(2), socket(2), accept_filter(9) HISTORY The accept() system call appeared in 4.2BSD. BSD December 11, 1993 BSD
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | HISTORY
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