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     close — delete a descriptor


     Standard C Library (libc, -lc)


     #include <unistd.h>

     close(int d);


     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

     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


     The close() system call will fail if:

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

     [EINTR]            An interrupt was received.

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

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


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


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


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