---
title: "fd_sync()"
description: "The fd_sync() function synchronizes the file and metadata associated with a file descriptor to disk. This ensures that any changes made to the file and its metadata are persisted and visible to other processes."
url: "https://wasix.org/docs/api-reference/wasi/fd_sync/"
markdown: "https://wasix.org/docs/api-reference/wasi/fd_sync.md"
---

# `fd_sync()`

Synchronize file and metadata to disk.

## Description

The `fd_sync()` function synchronizes the file and metadata associated with a file descriptor to disk. This ensures that any changes made to the file and its metadata are persisted and visible to other processes.

## Syntax

```ebnf
  ;;; Note: This is similar to `fsync` in POSIX.
  ;;; Synchronize the data and metadata of a file to disk.
  (@interface func (export "fd_sync")
    (param $fd $fd)
    (result $error (expected (error $errno)))
  )
```

## Parameters

- `ctx`: A mutable reference to the function environment.
- `fd`: The file descriptor to sync.

## Return Value

The function returns a `Result` indicating the success or failure of the operation. If the operation is successful, it returns `Errno::Success`. Otherwise, it returns an appropriate `Errno` value.

## Logging

This function has been instrumented with debug-level logging. It will log the following information:

- `%fd`: The file descriptor being synchronized.

## Note

The `fd_sync()` function synchronizes the file and metadata associated with the specified file descriptor (`fd`) to disk.

The function first retrieves the memory view and file system state from the WASI environment using the function context.

Next, it retrieves the file descriptor entry for the specified file descriptor from the file system state using the `get_fd()` method.

If the file descriptor does not have the `FD_SYNC` right, the function returns `Errno::Access` to indicate an access error.

The function then handles different cases based on the kind of the file descriptor’s associated inode:

- `Kind::File`: For file descriptors associated with regular files, the function retrieves the file handle and flushes it to ensure all pending changes are written to disk. It also updates the `FileStat` structure of the inode to reflect the correct current size of the file.

- `Kind::Root` or `Kind::Dir`: For file descriptors associated with directories, the function returns `Errno::Isdir` to indicate that synchronization is not applicable.

- Other kinds: For file descriptors associated with other types of inodes such as buffers, symlinks, sockets, pipes, or event notifications, the function returns `Errno::Inval` to indicate an invalid operation.

Finally, the function returns `Errno::Success` to indicate a successful operation.

---

[Documentation index](https://wasix.org/llms.txt) · [HTML version](https://wasix.org/docs/api-reference/wasi/fd_sync/)