NAME

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

SYNOPSIS

#include <unistd.h>

int fsync(int fildes);

DESCRIPTION

fsync moves all modified data and attributes of 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 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. 

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

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

ENOLINK fildes is on a remote machine and the link on that machine is no longer active. 

EINTR A signal was caught during execution of the fsync system call. 

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

DIAGNOSTICS

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

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. 

SEE ALSO

sync(2)