---
name: "sync"
section: "2"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/sync/2"
---

# sync(2)

commit filesystem caches to disk

## NAME

sync, syncfs - commit filesystem caches to disk

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <unistd.h>
```

**void sync(void);**

**int syncfs(int** *fd***);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**sync**():

```
    _XOPEN_SOURCE >= 500
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE
```

**syncfs**():

```
    _GNU_SOURCE
```

## DESCRIPTION

**sync**() causes all pending modifications to filesystem metadata and cached file data to be written to the underlying filesystems.

**syncfs**() is like **sync**(), but synchronizes just the filesystem containing file referred to by the open file descriptor *fd*.

## RETURN VALUE

**syncfs**() returns 0 on success; on error, it returns -1 and sets *errno* to indicate the error.

## ERRORS

**sync**() is always successful.

**syncfs**() can fail for at least the following reasons:

- **EBADF**

  *fd* is not a valid file descriptor.

- **EIO**

  An error occurred during synchronization. This error may relate to data written to any file on the filesystem, or on metadata related to the filesystem itself.

- **ENOSPC**

  Disk space was exhausted while synchronizing.

- **ENOSPC** **EDQUOT**

  Data was written to a file on NFS or another filesystem which does not allocate space at the time of a [**write**(2)](/write/2.md) system call, and some previous write failed due to insufficient storage space.

## VERSIONS

According to the standard specification (i.e., POSIX.1), **sync**() schedules the writes, but may return before the actual writing is done. However Linux waits for I/O completions, and thus **sync**() or **syncfs**() provide the same guarantees as **fsync**() called on every file in the system or filesystem respectively.

## STANDARDS

- **sync**()

  POSIX.1-2024.

- **syncfs**()

  Linux.

## HISTORY

- **sync**()

  POSIX.1-2001, SVr4, 4.3BSD.

- **syncfs**()

  Linux 2.6.39, glibc 2.14.

Since glibc 2.2.2, the Linux prototype for **sync**() is as listed above, following the various standards. In glibc 2.2.1 and earlier, it was "int sync(void)", and **sync**() always returned 0.

In mainline kernel versions prior to Linux 5.8, **syncfs**() will fail only when passed a bad file descriptor (**EBADF**). Since Linux 5.8, **syncfs**() will also report an error if one or more inodes failed to be written back since the last **syncfs**() call.

## BUGS

Before Linux 1.3.20, Linux did not wait for I/O to complete before returning.

## SEE ALSO

[**sync**(1)](/sync/1.md), [**fdatasync**(2)](/fdatasync/2.md), [**fsync**(2)](/fsync/2.md)