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     close — delete a descriptor


     Standard C Library (libc, -lc)


     #include <unistd.h>

     close(int fd);


     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.


     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.


     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.


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


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


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