FSYNC(2) BSD System Calls Manual FSYNC(2)
fsync — synchronise changes to a file
Standard C Library (libc, −lc)
The fsync() system call causes all modified data and attributes of 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 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.
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.
The fsync() fails if:
The fd argument is not a valid descriptor.
The fd argument refers to a socket, not to a file.
An I/O error occurred while reading from or writing to the file system.
The fsync() system call appeared in 4.2BSD.
BSD June 4, 1993 BSD