msync · shipping · also msync()

msync

msync is an operation that synchronizes a range of a shared file-backed memory mapping with its underlying file, with MS_SYNC waiting for completion.

On Linux, MS_ASYNC has been a no-op since 2.6.19 because dirty-page tracking already drives writeback; it is not a durability completion point. MAP_PRIVATE modifications do not update the backing file. MS_SYNC is not the distinct MAP_SYNC mapping flag used with DAX-capable files.

Relations

related

fsync, fdatasync, sync-file-range

Advantages

• Provides explicit synchronization for a selected mapped range.

Limitations

• The starting address must be page-aligned; portable callers specify exactly one of MS_SYNC and MS_ASYNC.
• Does not make private mapping changes persistent or provide an atomic application transaction.

Citations

1. Linux man-pages 6.19: msync(2), flags and Linux behavior (accessed 2026-10-13)
2. Linux man-pages 6.19: mmap(2), shared/private mappings and MAP_SYNC (accessed 2026-10-13)
3. Hesela: File and mapped-range synchronization boundaries (accessed 2026-10-13)

JSON: /data/terms/msync.json