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       close - close a file descriptor


       #include <unistd.h>

       int close(int fd);


       close()  closes  a  file  descriptor,  so  that it no longer refers to any file and may be
       reused.  Any record locks (see fcntl(2)) held on the file  it  was  associated  with,  and
       owned  by  the  process,  are  removed (regardless of the file descriptor that was used to
       obtain the lock).

       If fd is the last file descriptor referring to the underlying open file  description  (see
       open(2)),  the  resources  associated  with  the  open  file description are freed; if the
       descriptor was the last reference to a file which has been removed  using  unlink(2),  the
       file is deleted.


       close()   returns  zero  on  success.   On  error,  -1  is  returned,  and  errno  is  set


       EBADF  fd isn't a valid open file descriptor.

       EINTR  The close() call was interrupted by a signal; see signal(7).

       EIO    An I/O error occurred.


       POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.


       Not checking the return value of close() is a common but nevertheless serious  programming
       error.   It  is  quite  possible  that  errors  on a previous write(2) operation are first
       reported at the final close().  Not checking the return value when closing  the  file  may
       lead  to  silent  loss  of  data.   This can especially be observed with NFS and with disk
       quota.  Note that the return value should be used only  for  diagnostics.   In  particular
       close() should not be retried after an EINTR since this may cause a reused descriptor from
       another thread to be closed.

       A successful close does not guarantee that the data has been successfully saved  to  disk,
       as  the kernel defers writes.  It is not common for a filesystem to flush the buffers when
       the stream is closed.  If you need to be sure that the  data  is  physically  stored,  use
       fsync(2).  (It will depend on the disk hardware at this point.)

       It  is  probably unwise to close file descriptors while they may be in use by system calls
       in other threads in the same process.  Since a file descriptor may be  reused,  there  are
       some obscure race conditions that may cause unintended side effects.


       fcntl(2), fsync(2), open(2), shutdown(2), unlink(2), fclose(3)


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