---
name: "fsync"
section: "2freebsd"
platform: "linux"
package: "freebsd-manpages"
version: "12.2-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/fdatasync/2freebsd"
---

# fsync(2freebsd)

synchronise changes to a file

Part of [fdatasync(2freebsd)](/fdatasync/2freebsd.md).

## NAME

**fdatasync**, **fsync** – synchronise changes to a file

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<unistd.h\>**

*int*\

**fdatasync**(*int fd*);

*int*\

**fsync**(*int fd*);

## DESCRIPTION

The **fsync**() system call causes all modified data and attributes of the file referenced by the file descriptor *fd* to be moved to a permanent storage device. This normally results in all in-core modified copies of buffers for the associated file to be written to a disk.

The **fdatasync**() system call causes all modified data of *fd* to be moved to a permanent storage device. Unlike **fsync**(), the system call does not guarantee that file attributes or metadata necessary to access the file are committed to the permanent storage.

The **fsync**() system call should be used by programs that require a file to be in a known state, for example, in building a simple transaction facility. If the file metadata has already been committed, using **fdatasync**() can be more efficient than **fsync**().

Both **fdatasync**() and **fsync**() calls are cancellation points.

## RETURN VALUES

The **fsync()** function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

## ERRORS

The **fsync**() and **fdatasync**() calls fail if:

- \[EBADF\]

  The *fd* argument is not a valid descriptor.

- \[EINVAL\]

  The *fd* argument refers to a socket, not to a file.

- \[EIO\]

  An I/O error occurred while reading from or writing to the file system.

- \[EINTEGRITY\]

  Corrupted data was detected while reading from the file system.

## SEE ALSO

[fsync(1)](/fsync/1.md), [sync(2)](/sync/2.md), [syncer(4)](/syncer/4.md), [sync(8)](/sync/8.md)

## HISTORY

The **fsync**() system call appeared in 4.2BSD. The **fdatasync**() system call appeared in FreeBSD 11.1.

## BUGS

The **fdatasync**() system call currently does not guarantee that enqueued [aio(4)](/aio/4.md) requests for the file referenced by *fd* are completed before the syscall returns.