View Source: fsync(2) - Waikato Linux Users Group

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!!NAME


fsync, fdatasync - synchronize a file's complete in-core state with that on disk
!!SYNOPSIS


 __#include <unistd>__
 __int fsync(int__ ''fd''__);__

!!DESCRIPTION
fsync(2) copies all in-core parts of a file to disk, and waits until the device reports that all parts are on stable storage. It also updates metadata stat information. It does not necessarily ensure that the entry in the directory containing the file has also reached disk. For that an explicit fsync(2) on the file descriptor of the directory is also needed.

!!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 synchronization.
;[EIO]: An error occurred during synchronization.

!!NOTES
In case the hard disk has write cache enabled, the data may not really be on permanent storage when fsync(2) returns.

When an ext2 file system is mounted with the ''sync'' option, directory entries are also implicitely synced by fsync(2).

On kernels before 2.4, fsync(2) on big files can be inefficient. An alternative might be to use the ''O_SYNC'' flag to open(2).
!!CONFORMING TO
[POSIX].1b (formerly [POSIX].4)

!!SEE ALSO
bdflush(2), open(2), sync(2), mount(8), update(8), sync(8), fdatasync(2)
----
The difference between fsync(2) and fdatasync(2) is that fsync modifies the access time metadata in the i-node, while fdatasync doesn't/shouldn't. I think this is true version kernel versions >= 2.4 - for 2.2 and earlier fdatasync was the same as fsync.

13 pages link to fsync(2):

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Last edited on Thursday, November 7, 2002 4:22:59 pm by JohnMcPherson

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