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CLOSE(2)                   Linux Programmer's Manual                  CLOSE(2)

       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 appropriately.

       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.

       SVr4, 4.3BSD, POSIX.1-2001.

       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.

       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 file system 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 re-used, there are some obscure race conditions that may
       cause unintended side effects.

       When dealing with sockets, you have to be sure that there is no recv(2) still blocking on it on another thread,
       otherwise  it  might  block  forever,  since no more messages will be sent via the socket. Be sure to use shut-
       down(2) to shut down all parts the connection before closing the socket.

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

       This page is part of release 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at

Linux                             2007-12-28                          CLOSE(2)