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- .Dd December 1, 2017
- .Dt SYNC 2
- .Os
- .Sh NAME
- .Nm sync
- .Nd "schedule file system updates"
- .Sh LIBRARY
- .Lb libc
- .Sh SYNOPSIS
- .In unistd.h
- .Ft void
- .Fn sync void
- .Sh DESCRIPTION
- The
- .Fn sync
- system call forces a write of dirty (modified) buffers
- in the block buffer cache out
- to disk.
- The kernel keeps this information in core to reduce
- the number of disk I/O transfers required by the system.
- As information in the cache is lost after a system crash, a
- .Fn sync
- system call is issued
- frequently
- by the kernel process
- .Xr syncer 4
- (about every 30 seconds).
- .Pp
- The
- .Xr fsync 2
- system call
- may be used to synchronize individual file descriptor
- attributes.
- .Sh SEE ALSO
- .Xr fsync 2 ,
- .Xr syncer 4 ,
- .Xr sync 8
- .Sh HISTORY
- The
- .Fn sync
- function appeared in
- .At v3 .
- .Sh BUGS
- The
- .Fn sync
- system call
- may return before the buffers are completely flushed.
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