fsync(3C)

NAME

     fsync - synchronize changes to a file

SYNOPSIS

     #include <unistd.h>

     int fsync(int fildes);

DESCRIPTION

     The fsync() function moves all modified data and  attributes
     of  the  file  descriptor  fildes  to a storage device. When
     fsync() returns, all in-memory modified  copies  of  buffers
     associated  with  fildes  have  been written to the physical
     medium. The fsync() function is different from sync(), which
     schedules disk I/O for all files  but returns before the I/O
     completes. The fsync() function forces all outstanding  data
     operations  to  synchronized  file integrity completion (see
     fcntl(3HEAD) definition of O_SYNC.)

     The fsync() function forces all currently queued I/O  opera-
     tions  associated  with  the  file  indicated  by  the  file
     descriptor fildes to the synchronized I/O completion  state.
     All I/O operations are completed as defined for synchronized
     I/O file integrity completion.

RETURN VALUES

     Upon successful completion, 0 is returned. Otherwise, -1  is
     returned  and  errno  is  set  to indicate the error. If the
     fsync() function fails, outstanding I/O operations  are  not
     guaranteed to have been completed.

ERRORS

     The fsync() function will fail if:

     EBADF The fildes argument is not a valid file descriptor.

     EINTR A signal was caught during execution  of  the  fsync()
           function.

     EIO   An I/O error occurred while reading from or writing to
           the file system.

     ENOSPC
           There was no free space remaining on the  device  con-
           taining the file.

     ETIMEDOUT
           Remote connection timed out. This occurs when the file
           is  on  an   NFS  file  system  mounted with the  soft
           option. See  mount_nfs(1M).

     In the event that any of the  queued  I/O  operations  fail,
     fsync() returns the error conditions defined for read(2) and
     write(2).

USAGE

     The fsync() function should be  used  by  applications  that
     require  that  a  file  be in a known state. For example, an
     application that  contains  a  simple  transaction  facility
     might  use   fsync() to ensure that all changes to a file or
     files caused by a  given  transaction  were  recorded  on  a
     storage medium.

     The manner in which  the  data  reach  the  physical  medium
     depends  on  both  implementation and hardware.  The fsync()
     function returns when notified by the device driver that the
     write has taken place.

     When a UFS file system is mounted with logging enabled, file
     system  transactions  that  free blocks from files might not
     actually add those freed blocks to the  file  system's  free
     list  until  some  unspecified  time  in  the  future.  This
     behavior improves file system performance but does not  con-
     form  to the POSIX, Single UNIX Specification, SPARC Confor-
     mance Definition, System  V  Application  Binary  Interface,
     System  V Interface Definition, and X/Open Portability Guide
     Standards, which  require  that  freed  space  be  available
     immediately.  To enable standards conformance regarding file
     deletions or to address the problem of  not  being  able  to
     grow  files  on a relatively full UFS file system even after
     files  have  been  deleted,   disable   UFS   logging   (see
     mount_ufs(1M).

ATTRIBUTES

     See attributes(5) for descriptions of the  following  attri-
     butes:

     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | MT-Level                    | Async-Signal-Safe           |
    |_____________________________|_____________________________|

SEE ALSO

     mount_nfs(1M), mount_ufs(1M),  read(2),  sync(2),  write(2),
     fcntl(3HEAD), fdatasync(3RT), attributes(5)