Linux man pages : sync (2)
SYNC(2) Linux Programmer's Manual SYNC(2)
sync - commit buffer cache to disk.
sync first commits inodes to buffers, and then buffers to disk.
SVr4, SVID, X/OPEN, BSD 4.3
According to the standard specification (e.g., SVID), 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.)
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.
bdflush(2), fsync(2), fdatasync(2), update(8), sync(8)
Linux 2.4 2001-10-10 SYNC(2)