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HP-UX 11i Version 3: February 2007

Technical documentation

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sync, lsync — update disk


#include <unistd.h>

void sync(void);

void lsync(void);


sync() causes all information in memory that should be on disk to be written out. This includes modified file system meta-data and delayed block I/O.

It should be used by commands and programs that examine a file system, such as fsck, df, and so on. It is mandatory before a shutdown.

The writing, although scheduled, is not necessarily complete upon return from sync().

In some HP-UX systems, sync() may be reduced to a no-op. This is permissible on a system which does not cache buffers or in a system that in some way ensures that the disks are always in a consistent state.

lsync() is a deprecated system call that is currently functionally identical to sync(). HP-UX kernel support for it remains only to aid compatibility with very old HP-UX binaries.


sync() was developed by HP and AT&T Bell Laboratories.


sync(1M), fdatasync(2), fsync(2).


sync(): SVID2, SVID3, XPG2

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