bionic (2) close.2freebsd.gz

NAME

     close — delete a descriptor

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <unistd.h>

     int
     close(int fd);

DESCRIPTION

     The close() system call deletes a descriptor from the per-process object reference table.  If this is the
     last reference to the underlying object, the object will be deactivated.  For example, on the last close of
     a file the current seek pointer associated with the file is lost; on the last close of a socket(2)
     associated naming information and queued data are discarded; on the last close of a file holding an
     advisory lock the lock is released (see further flock(2)).  However, the semantics of System V and IEEE Std
     1003.1-1988 (“POSIX.1”) dictate that all fcntl(2) advisory record locks associated with a file for a given
     process are removed when any file descriptor for that file is closed by that process.

     When a process exits, all associated file descriptors are freed, but since there is a limit on active
     descriptors per processes, the close() system call is useful when a large quantity of file descriptors are
     being handled.

     When a process forks (see fork(2)), all descriptors for the new child process reference the same objects as
     they did in the parent before the fork.  If a new process is then to be run using execve(2), the process
     would normally inherit these descriptors.  Most of the descriptors can be rearranged with dup2(2) or
     deleted with close() before the execve(2) is attempted, but if some of these descriptors will still be
     needed if the execve fails, it is necessary to arrange for them to be closed if the execve succeeds.  For
     this reason, the call “fcntl(d, F_SETFD, FD_CLOEXEC)” is provided, which arranges that a descriptor will be
     closed after a successful execve; the call “fcntl(d, F_SETFD, 0)” restores the default, which is to not
     close the descriptor.

RETURN VALUES

     The close() function returns the value 0 if successful; otherwise the value -1 is returned and the global
     variable errno is set to indicate the error.

ERRORS

     The close() system call will fail if:

     [EBADF]            The fd argument is not an active descriptor.

     [EINTR]            An interrupt was received.

     [ENOSPC]           The underlying object did not fit, cached data was lost.

     [ECONNRESET]       The underlying object was a stream socket that was shut down by the peer before all
                        pending data was delivered.

     In case of any error except EBADF, the supplied file descriptor is deallocated and therefore is no longer
     valid.

SEE ALSO

     accept(2), closefrom(2), execve(2), fcntl(2), flock(2), open(2), pipe(2), socket(2), socketpair(2)

STANDARDS

     The close() system call is expected to conform to ISO/IEC 9945-1:1990 (“POSIX.1”).

HISTORY

     The close() function appeared in Version 7 AT&T UNIX.