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), sync(2), syncer(4), sync(8)

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) requests for the file
       referenced by fd are completed before the syscall returns.

Debian                                           March 30, 2020                                         FSYNC(2)