fdatasync

FDATASYNC(2)		  Linux Programmer’s Manual		 FDATASYNC(2)



NAME
       fdatasync - synchronize a file’s in-core data with that on disk

SYNOPSIS
       #include <unistd.h>

       int fdatasync(int fd);

DESCRIPTION
       fdatasync  flushes all data buffers of a file to disk (before the sys-
       tem call returns).  It resembles fsync but is not required  to  update
       the metadata such as access time.

       Applications  that  access  databases  or log files often write a tiny
       data fragment (e.g., one line in a log file) and then call fsync imme-
       diately	in order to ensure that the written data is physically stored
       on the harddisk. Unfortunately, fsync will always initiate  two	write
       operations: one for the newly written data and another one in order to
       update the modification time stored in the inode. If the	 modification
       time is not a part of the transaction concept fdatasync can be used to
       avoid unnecessary inode disk write operations.

RETURN VALUE
       On success, zero is returned.  On error, -1 is returned, and errno  is
       set appropriately.

ERRORS
       EBADF  fd is not a valid file descriptor open for writing.

       EROFS, EINVAL
	      fd  is  bound to a special file which does not support synchro-
	      nization.

       EIO    An error occurred during synchronization.

BUGS
       Currently (Linux 2.2) fdatasync is equivalent to fsync.

AVAILABILITY
       On POSIX systems on  which  fdatasync  is  available,  _POSIX_SYNCHRO-
       NIZED_IO is defined in <unistd.h> to a value greater than 0. (See also
       sysconf(3).)

CONFORMING TO
       POSIX1b (formerly POSIX.4)

SEE ALSO
       fsync(2), B.O. Gallmeister, POSIX.4, O’Reilly, pp. 220-223 and 343.



Linux 1.3.86			  1996-04-13			 FDATASYNC(2)