close-to-open-consistency · shipping · also CTO consistency, close-to-open cache consistency

Close-to-open consistency

Close-to-open consistency is a file-sharing cache policy that combines writeback at close with validation at a later open to support visibility of updates between sequential users.

Related Observatory article: Close-to-open consistency on hesela.com

An already-open reader is a different case from a new opener. Concurrent access needs application coordination; CTO alone does not serialize simultaneous writers. Linux documents NFSv3 open-time checks and close-time writeback, while NFSv4 delegations can avoid repeated validation and defer writeback. Persistence still depends on the applicable protocol and error handling.

Relations

related

nfs-storage, nfs-attribute-cache, nfs-delegation, nfs-commit

Limitations

• Linux cto/nocto options differ by version: the NFSv4 setting concerns directories, not file-data caching. [1]

Citations

1. nfs-utils nfs(5), Debian trixie: data and metadata coherence and version-specific cto/nocto options. (accessed 2026-10-14)
2. Haynes and Noveck (editors). NFS Version 4 Protocol. RFC 7530, sections 10.3, 10.4 and 10.6 (NFSv4.0). (accessed 2026-10-14)
3. Noveck and Lever (editors). NFS Version 4 Minor Version 1 Protocol. RFC 8881, sections 10.3-10.6 (NFSv4.1). (accessed 2026-10-14)
4. NFS stable writes: what COMMIT, flush and FUA actually promise (accessed 2026-10-14)

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