sync, syncfs - commit filesystem caches to disk
syncfs() returns 0 on success; on error, it returns -1 and sets
errno to indicate the error.
syncfs() first appeared in Linux 2.6.39; library support was added to glibc in version 2.14.
According to the standard specification (e.g., POSIX.1-2001), sync() schedules the writes, but may return before the actual writing is done. However Linux waits for I/O completions, and thus sync() or syncfs() provide the same guarantees as fsync called on every file in the system or filesystem respectively.
Before version 1.3.20 Linux did not wait for I/O to complete before returning.
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