fsync(3C) manual page
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fsync - synchronize a file’s in-memory state with that on the physical
medium
#include <unistd.h>
int fsync(int fildes);
Async-Signal-Safe
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.
Upon successful completion, a value of
0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate
the error.
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)
.
mount_nfs(1M)
,
sync(2)
, fdatasync(3R)
, fcntl(5)
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.
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