NAME

fsync − synchronize a file’s in-memory state with that on the physical medium

SYNOPSIS

#include <unistd.h>

int fsync(int fildes);

MT-LEVEL

Async-Signal-Safe

DESCRIPTION

fsync() moves all modified data and attributes of the file descriptor fildes to a storage device.  When fsync() returns, all in-memory modified copies of buffers associated with fildes have been written to the physical medium.  fsync() is different from sync(), which schedules disk I/O for all files but returns before the I/O completes.  fsync() forces all outstanding data operations to synchronized file integrity completion (see fcntl(5) definition of O_SYNC.) 

fsync() should be used by programs that require that a file be in a known state.  For example, a program that contains a simple transaction facility might use fsync() to ensure that all changes to a file or files caused by a given transaction were recorded on a storage medium. 

RETURN VALUES

Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error. 

ERRORS

fsync() fails if one or more of the following are true:

EBADF fildes is not a valid file descriptor open for writing. 

EINTR A signal was caught during execution of the fsync() function. 

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

ETIMEDOUT Remote connection timed out. This occurs when the file is on an NFS file system mounted with the soft option.  See mount_nfs(1M). 

SEE ALSO

mount_nfs(1M), sync(2), fdatasync(3R), fcntl(5)

NOTES

The way the data reach the physical medium depends on both implementation and hardware.  fsync() returns when the device driver tells it that the write has taken place. 

SunOS 5.5.1  —  Last change: 14 Feb 1996