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sync - commit buffer cache to disk
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
sync(): _BSD_SOURCE || _XOPEN_SOURCE >= 500
sync() first commits inodes to buffers, and then buffers to disk.
This function is always successful.
SVr4, 4.3BSD, POSIX.1-2001.
Since glibc 2.2.2 the Linux prototype is as listed above, following the
various standards. In libc4, libc5, and glibc up to 2.2.1 it was "int
sync(void)", and sync() always returned 0.
According to the standard specification (e.g., POSIX.1-2001), sync()
schedules the writes, but may return before the actual writing is done.
However, since version 1.3.20 Linux does actually wait. (This still
does not guarantee data integrity: modern disks have large caches.)
bdflush(2), fdatasync(2), fsync(2), sync(8), update(8)
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