Glossary

Archive mode — -a, the bundle -rlptgoD: recursive, links, permissions, times, group, owner, devices/specials. The sane default.

Daemon — rsync running as a server, serving named modules over its own protocol (port 873 by default), without a shell account or encryption.

Delta transfer — sending only the changed blocks of a file, found by comparing rolling checksums. Used over the network; local copies default to whole-file instead.

Dry run — -n / --dry-run: the full comparison and listing, with nothing transferred, changed, or deleted.

Exclude / include — filter rules (--exclude, --include) that keep paths out of (or rescue paths into) the transfer, matched in order, first match wins.

File list — the inventory rsync builds of the source before comparing it with the destination.

Hardlink — a second (or third) name for the same file data: same inode, shared content. Preserved across a sync only with -H; created on purpose by --link-dest.

Inode — the filesystem's identifier for a file's data. Two names with the same inode are the same file; ls -li shows it.

Itemize changes — --itemize-changes, the 11-character code prefixed to each listing line describing what changed and why.

Link-dest — --link-dest=DIR: compare against a previous tree and hardlink unchanged files from it into the new one. The snapshot mechanism.

Literal data — bytes actually sent for a file because the receiver didn't already hold matching blocks. Its counterpart is matched data: bytes rebuilt from the receiver's existing copy.

Module — a directory plus rules (path, read-only, who may connect) that an rsync daemon serves under a name.

Partial — --partial: keep the transferred portion of an interrupted file so the next run resumes from it instead of starting over.

Quick check — rsync's default change test: same size and same modification time means unchanged, contents never read.

Rolling checksum — the sliding-window checksum that lets the sender find matching blocks in a changed file even after insertions shift everything downstream.

Snapshot (rsync sense) — a complete copy of a tree at a moment, built with --link-dest so unchanged files are hardlinks to the previous snapshot and cost no new disk.

Speedup — the summary's ratio of total size to bytes actually moved; around 1 for a first copy, large when a run mostly compared.

Trailing slash — the / on the source path that switches rsync between "copy this directory" (no slash) and "copy its contents" (slash).