fsync(2)                                                              fsync(2)


NAME
     fsync, fdatasync - synchronize a file's in-memory state with that on the
     physical medium

SYNOPSIS
     #include <unistd.h>

     int fsync(int fildes);
     int fdatasync(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.

     fdatasync is the same as  fsync, except that it only moves all the
     modified data, and not the attributes of fildes to a storage device.

     fsync  and fdatasync fail 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                    is no longer active.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 system call.

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

     EINVAL         fildes is not a valid descriptor Synchronized I/O.

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)


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