{
  "slug": "rsync-quick-check",
  "term": "Rsync quick check",
  "aliases": [
    "rsync file-selection heuristic"
  ],
  "definition": "Rsync quick check is the regular-file selection heuristic that normally treats matching file size and modification time as sufficient to skip transferring file data.",
  "note": "The default timestamp comparison uses integer seconds; --modify-window=-1 also compares nanoseconds when the receiver supports it (3.1.3 or later). Finer precision cannot detect changed bytes whose timestamp is exactly preserved. --checksum selects using file contents instead of mtime for equal-size files, adding read work. [manual]\n\nSelection precedes delta transfer. In rsync v3.2.7, the regular-file quick_check_ok path tests size mismatch, checksum, size-only, ignore-times and mtime in that order. Combining --size-only with --ignore-times does not force equal-size files into transfer; combining --checksum with --ignore-times can still skip identical content. [generator]\n\nHesela checked these boundaries with 42 constructed native runs, exact-byte comparisons and preserved timestamp controls. Every run returned zero, including metadata-selected skips that retained different destination bytes. This is a scoped software observation, not a rate of backup failures. Transfer verification does not validate the contents of metadata-skipped files. [study]",
  "related": [
    "delta-synchronization",
    "checksum",
    "backup-verification"
  ],
  "citations": [
    {
      "id": "manual",
      "title": "Rsync v3.2.7 manual: ignore-times, size-only, modify-window and checksum.",
      "url": "https://github.com/RsyncProject/rsync/blob/v3.2.7/rsync.1.md",
      "accessed": "2026-10-20"
    },
    {
      "id": "generator",
      "title": "Rsync v3.2.7 generator.c: quick_check_ok.",
      "url": "https://github.com/RsyncProject/rsync/blob/v3.2.7/generator.c#L585-L607",
      "accessed": "2026-10-20"
    },
    {
      "id": "study",
      "title": "Hesela: native rsync file-selection matrix and reproduction bundle.",
      "url": "https://hesela.com/analyses/rsync-delta-shifted-blocks/#selection",
      "accessed": "2026-10-20"
    }
  ],
  "status": "shipping",
  "advantages": [
    "Avoids reading every matching-size file solely to decide whether it needs transfer."
  ],
  "limitations": [
    "Matching metadata is not a content-integrity proof.",
    "Different selection flags can have precedence rather than last-option-wins behavior."
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-20"
}