from small one page howto to huge articles all in one place
 

search text in:





Poll
Which filesystem do you use?






poll results

Last additions:
using iotop to find disk usage hogs

using iotop to find disk usage hogs

words:

887

views:

193478

userrating:

average rating: 1.7 (102 votes) (1=very good 6=terrible)


May 25th. 2007:
Words

486

Views

251680

why adblockers are bad


Workaround and fixes for the current Core Dump Handling vulnerability affected kernels

Workaround and fixes for the current Core Dump Handling vulnerability affected kernels

words:

161

views:

140551

userrating:

average rating: 1.4 (42 votes) (1=very good 6=terrible)


April, 26th. 2006:

Druckversion
You are here: manpages





FSYNC

Section: Linux Programmer's Manual (2)
Updated: 2017-09-15
Index Return to Main Contents
 

NAME

fsync, fdatasync - synchronize a file's in-core state with storage device  

SYNOPSIS

#include <unistd.h>

int fsync(int fd);

int fdatasync(int fd);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

fsync():
    Glibc 2.16 and later:
        No feature test macros need be defined
    Glibc up to and including 2.15:
        _BSD_SOURCE || _XOPEN_SOURCE
            || /* since glibc 2.8: */ _POSIX_C_SOURCE >= 200112L
fdatasync():
    _POSIX_C_SOURCE >= 199309L || _XOPEN_SOURCE >= 500  

DESCRIPTION

fsync() transfers ("flushes") all modified in-core data of (i.e., modified buffer cache pages for) the file referred to by the file descriptor fd to the disk device (or other permanent storage device) so that all changed information can be retrieved even if the system crashes or is rebooted. This includes writing through or flushing a disk cache if present. The call blocks until the device reports that the transfer has completed.

As well as flushing the file data, fsync() also flushes the metadata information associated with the file (see inode(7)).

Calling fsync() does not necessarily ensure that the entry in the directory containing the file has also reached disk. For that an explicit fsync() on a file descriptor for the directory is also needed.

fdatasync() is similar to fsync(), but does not flush modified metadata unless that metadata is needed in order to allow a subsequent data retrieval to be correctly handled. For example, changes to st_atime or st_mtime (respectively, time of last access and time of last modification; see inode(7)) do not require flushing because they are not necessary for a subsequent data read to be handled correctly. On the other hand, a change to the file size (st_size, as made by say ftruncate(2)), would require a metadata flush.

The aim of fdatasync() is to reduce disk activity for applications that do not require all metadata to be synchronized with the disk.  

RETURN VALUE

On success, these system calls return zero. On error, -1 is returned, and errno is set appropriately.  

ERRORS

EBADF
fd is not a valid open file descriptor.
EIO
An error occurred during synchronization.
EROFS, EINVAL
fd is bound to a special file (e.g., a pipe, FIFO, or socket) which does not support synchronization.
 

CONFORMING TO

POSIX.1-2001, POSIX.1-2008, 4.3BSD.  

AVAILABILITY

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

NOTES

On some UNIX systems (but not Linux), fd must be a writable file descriptor.

In Linux 2.2 and earlier, fdatasync() is equivalent to fsync(), and so has no performance advantage.

The fsync() implementations in older kernels and lesser used filesystems does not know how to flush disk caches. In these cases disk caches need to be disabled using hdparm(8) or sdparm(8) to guarantee safe operation.  

SEE ALSO

sync(1), bdflush(2), open(2), posix_fadvise(2), pwritev(2), sync(2), sync_file_range(2), fflush(3), fileno(3), hdparm(8), mount(8)  

COLOPHON

This page is part of release 4.13 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
CONFORMING TO
AVAILABILITY
NOTES
SEE ALSO
COLOPHON





Support us on Content Nation
rdf newsfeed | rss newsfeed | Atom newsfeed
- Powered by LeopardCMS - Running on Gentoo -
Copyright 2004-2020 Sascha Nitsch Unternehmensberatung GmbH
Valid XHTML1.1 : Valid CSS : buttonmaker
- Level Triple-A Conformance to Web Content Accessibility Guidelines 1.0 -
- Copyright and legal notices -
Time to create this page: 14.4 ms