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

NAME         top

       close - close a file descriptor

SYNOPSIS         top

       #include <unistd.h>

       int close(int fd);

DESCRIPTION         top

       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 file descriptor was the last
       reference to a file which has been removed using unlink(2), the file
       is deleted.

RETURN VALUE         top

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

ERRORS         top

       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.

CONFORMING TO         top

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

NOTES         top

       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 file 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 uses the buffer cache to
       defer writes.  Typically, filesystems do not flush buffers when a
       file is closed.  If you need to be sure that the data is physically
       stored on the underlying disk, use fsync(2).  (It will depend on the
       disk hardware at this point.)

       The close-on-exec file descriptor flag can be used to ensure that a
       file descriptor is automatically closed upon a successful execve(2);
       see fcntl(2) for details.

       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.

SEE ALSO         top

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

COLOPHON         top

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Linux                            2016-10-08                         CLOSE(2)