fsync(3c) [opensolaris man page]
fsync(3C) Standard C Library Functions 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.h(3HEAD) definition of O_SYNC.) The fsync() function forces all currently queued I/O operations 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 containing 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. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Committed | +-----------------------------+-----------------------------+ |MT-Level |Async-Signal-Safe | +-----------------------------+-----------------------------+ |Standard |See standards(5). | +-----------------------------+-----------------------------+ SEE ALSO
mount_nfs(1M), read(2), sync(2), write(2), fcntl.h(3HEAD), fdatasync(3C), attributes(5), standards(5) SunOS 5.11 5 Feb 2008 fsync(3C)
Check Out this Related Man Page
FSYNC(3P) POSIX Programmer's Manual FSYNC(3P) PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond- ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux. NAME
fsync - synchronize changes to a file SYNOPSIS
#include <unistd.h> int fsync(int fildes); DESCRIPTION
The fsync() function shall request that all data for the open file descriptor named by fildes is to be transferred to the storage device associated with the file described by fildes in an implementation-defined manner. The fsync() function shall not return until the system has completed that action or until an error is detected. If _POSIX_SYNCHRONIZED_IO is defined, the fsync() function shall force all currently queued I/O operations associated with the file indi- cated by file descriptor fildes to the synchronized I/O completion state. All I/O operations shall be completed as defined for synchronized I/O file integrity completion. RETURN VALUE
Upon successful completion, fsync() shall return 0. Otherwise, -1 shall be returned and errno 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 shall fail if: EBADF The fildes argument is not a valid descriptor. EINTR The fsync() function was interrupted by a signal. EINVAL The fildes argument does not refer to a file on which this operation is possible. EIO An I/O error occurred while reading from or writing to the file system. In the event that any of the queued I/O operations fail, fsync() shall return the error conditions defined for read() and write(). The following sections are informative. EXAMPLES
None. APPLICATION USAGE
The fsync() function should be used by programs which require modifications to a file to be completed before continuing; for example, a program which contains a simple transaction facility might use it to ensure that all modifications to a file or files caused by a transac- tion are recorded. RATIONALE
The fsync() function is intended to force a physical write of data from the buffer cache, and to assure that after a system crash or other failure that all data up to the time of the fsync() call is recorded on the disk. Since the concepts of "buffer cache", "system crash", "physical write", and "non-volatile storage" are not defined here, the wording has to be more abstract. If _POSIX_SYNCHRONIZED_IO is not defined, the wording relies heavily on the conformance document to tell the user what can be expected from the system. It is explicitly intended that a null implementation is permitted. This could be valid in the case where the system cannot assure non-volatile storage under any circumstances or when the system is highly fault-tolerant and the functionality is not required. In the middle ground between these extremes, fsync() might or might not actually cause data to be written where it is safe from a power fail- ure. The conformance document should identify at least that one configuration exists (and how to obtain that configuration) where this can be assured for at least some files that the user can select to use for critical data. It is not intended that an exhaustive list is required, but rather sufficient information is provided so that if critical data needs to be saved, the user can determine how the system is to be configured to allow the data to be written to non-volatile storage. It is reasonable to assert that the key aspects of fsync() are unreasonable to test in a test suite. That does not make the function any less valuable, just more difficult to test. A formal conformance test should probably force a system crash (power shutdown) during the test for this condition, but it needs to be done in such a way that automated testing does not require this to be done except when a formal record of the results is being made. It would also not be unreasonable to omit testing for fsync(), allowing it to be treated as a qual- ity-of-implementation issue. FUTURE DIRECTIONS
None. SEE ALSO
sync(), the Base Definitions volume of IEEE Std 1003.1-2001, <unistd.h> COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html . IEEE
/The Open Group 2003 FSYNC(3P)