Penguin

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.

This page is a man page (or other imported legacy content). We are unable to automatically determine the license status of this page.