193 lines
9.3 KiB
Markdown
193 lines
9.3 KiB
Markdown
# WARNING
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THIS TOOL IS COMPLETELY VIBE-CODED!!!
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THESE LINES ARE THE ONLY ONE I HAVE WRITTEN MYSELF!!!!
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I SWEAR I DID NOT READ MORE THAN 20 LINES OF CODE!
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USE AT YOUR OWN RISK (AS ALWAYS)
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I needed a Tool to sync 2 Files from a to b with differential transfer, all managed from a workstation c.
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Maybe i use this to learn go...
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Looks nice, builds fast, runs everywhere with one Binary.
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# clonetool
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Block-level sync for a large file or block device between two machines (or
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two paths on the same machine), driven from a third, passive "manager"
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machine. Single static Go binary, no runtime dependencies beyond the
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system `ssh` client for remote endpoints. Linux only.
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## How it works
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- You run `clonetool sync` on the **manager**. Source, destination, and
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manager may be three entirely different machines — the manager never
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reads or writes a single block itself. It only spawns and talks to two
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**control agents** (`clonetool agent --role control`, one per side,
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local subprocess or over `ssh`) that do the stat/prepare/transfer work.
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- The two agents compare content by **SHA-256 hash per fixed-size block**.
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A block is only re-read once: it's hashed from the buffer it was read
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into, and that same buffer is what gets sent on if it differs — never
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read twice.
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- **Source and destination are scanned in parallel.** The destination side
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streams the hash of each block *as it computes it*, in block order; the
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source side consumes that stream and immediately reads, compares and (if
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it differs) sends that block. So the destination scan, the source scan
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and the transfer of changed blocks all overlap — there is no "scan the
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whole destination, then start" phase. The status line shows the transfer
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progress with a trailing `scan H/M` until the destination fingerprint is
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complete.
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- **No state is kept between runs.** Every sync re-reads and re-hashes the
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destination's *current* content and compares the source against that, so
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a re-run only moves the blocks that actually differ and nothing needs to
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be trusted from a previous run. (The destination side always does the
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destination hashing — the remote `sink` in push mode, the local
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destination agent in pull mode.)
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- Bulk data goes **directly between source and destination**, not through
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the manager. Each run tries:
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1. **push** — the source agent connects straight to the destination
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host over SSH and streams changed blocks to it.
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2. **pull** (fallback) — if push isn't possible (no route/keys in that
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direction), the destination agent connects to the source host
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instead and pulls.
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3. If neither direction works, the job fails with both reasons named.
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Run the manager on the source or destination host, or set up SSH
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connectivity in at least one direction.
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- When source and destination are **both local** to the manager, no SSH
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is used at all — the source agent spawns the write-side helper as a
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plain local subprocess.
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- **Self-deploy:** if a remote endpoint has no runnable `clonetool` on
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`PATH` (or wherever `--remote-bin` points), **or the one that's there is
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a different build than this binary** (see below), the manager streams
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*this* binary to `~/.clonetool/bin/clonetool` on that host over the
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existing SSH connection and uses it — no install, no root. Disable with
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`--deploy=false` (a stale or missing binary is then an error, except a
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merely-stale `--remote-bin` is used anyway with a warning, since there's
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no way to correct it). If the copied binary won't execute there (wrong
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CPU architecture) the error says so; build one for the remote's arch
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(`CGO_ENABLED=0 GOOS=linux GOARCH=arm64 go build`) and put it on `PATH`
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or pass `--remote-bin`.
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- **Version/staleness check:** every binary has a build timestamp baked in
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(see Build below) and `clonetool version` prints it. Before using a
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remote `clonetool`, the manager runs its `version` there and compares
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that timestamp against its own — a mismatch (e.g. the remote was
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self-deployed from an older build of this tool) is treated the same as
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"not runnable" and triggers the self-deploy above, so the remote binary
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is kept in sync with whatever you're running locally. Only the build
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timestamp is compared, not `GOARCH` — that is expected to differ across
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a cross-compiled deploy.
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- **sudo:** if reading or writing an endpoint that is a **block device**
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fails with a permission error, `--sudo=auto` (the default) transparently
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restarts that side's agent — and the helper it spawns on the peer —
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under `sudo`. Locally that may prompt for a password on your terminal;
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**on a remote host it uses `sudo -n`, so passwordless sudo (NOPASSWD)
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must be configured there** (a password prompt can't work — the transfer
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protocol owns the SSH stdout stream). `--sudo=always` elevates from the
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start; `--sudo=never` never does.
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- Sizing rules:
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- Destination is a **block device**: it can't be resized, so if the
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source is larger the job fails; otherwise exactly the source's size is
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synced and the remainder of the device is left untouched.
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- Destination is a **regular file**: it's truncated (created if
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missing) to exactly the source's size, growing or shrinking it.
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Shrinking an existing non-empty file prompts for confirmation unless
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`--yes` is passed.
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## Build
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```
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CGO_ENABLED=0 go build -o clonetool .
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```
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Cross-compile for another architecture by setting `GOARCH` (no cgo, so
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this works from any host):
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```
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CGO_ENABLED=0 GOOS=linux GOARCH=arm64 go build -o clonetool .
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```
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`./build.sh` writes linux/amd64 and linux/arm64 binaries into `dist/`. It
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also stamps every binary it builds with the same build timestamp (via
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`-ldflags -X main.buildTime=...`), which is how the manager tells a stale
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self-deployed remote binary apart from a current one (see "Version/staleness
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check" above) — build all your binaries for a given release with one
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`./build.sh` run so they compare equal to each other. A plain `go build`
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with no `-ldflags` leaves the timestamp at `"dev"`, which still works for
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this check (it only ever compares equal to another literal copy of the same
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`dev` binary, never to a real timestamp).
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Copy the resulting binary to the manager host. Source and destination
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hosts get it automatically (see self-deploy above), or place it yourself
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and point `--remote-bin` at it. The binary is architecture-specific —
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cross-compile if your hosts differ.
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## Usage
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```
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clonetool sync --source LOC --dest LOC [options]
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```
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`LOC` is either a local path (`/dev/sdb`, `./image.bin`) or
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`[user@]host:path` for a path reached over SSH.
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```
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# Same machine
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clonetool sync --source /dev/sda --dest /dev/sdb
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# Whole disk to an image file
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clonetool sync --source /dev/sda --dest /srv/sda.img
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# Two remote machines, orchestrated from a third
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clonetool sync --source db1:/dev/vdb --dest backup-host:/srv/db1.img
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# Re-run any time; only changed blocks move
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clonetool sync --source db1:/dev/vdb --dest backup-host:/srv/db1.img
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```
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Options:
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| Flag | Default | Meaning |
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| `--block-size` | `4M` | Block size (accepts `K`/`M`/`G` suffixes). |
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| `--job` | — | Optional label shown in progress/log output. |
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| `--yes` | off | Don't prompt before shrinking an existing destination file. |
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| `--sudo` | `auto` | Block-device privilege escalation: `auto` (on a permission error), `always`, or `never`. Remote elevation needs passwordless sudo. |
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| `--deploy` | `true` | Copy this binary to remote hosts that lack a runnable `clonetool`. `--deploy=false` to disable. |
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| `--connect-timeout` | `8` | SSH connect timeout (seconds) used for the push/pull direction probe. |
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| `--ssh` | `ssh` | ssh binary to use. |
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| `--ssh-opt` | — | Extra `-o OPT` passed to ssh (repeatable). |
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| `--remote-bin` | `clonetool` | Path to clonetool on remote hosts. |
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| `--manager-host` | local hostname | Address a peer should use to reach this machine, needed only when source or dest is local to the manager *and* the other side is remote and ends up needing to dial back in (pull fallback). |
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`clonetool version` prints the binary's `GOOS/GOARCH` and build timestamp,
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e.g. `clonetool linux/amd64 build=2024-06-01T12:00:00Z` (the timestamp is
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used internally for the self-deploy staleness check above).
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The status line shows read throughput for both sides and write throughput
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for the destination separately: `rd(src)` is the source reading and
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comparing its blocks, `rd(dst)` is the destination fingerprinting its
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current content (only while the trailing `scan H/M` segment is present),
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and `wr(dst)` is the destination actually writing changed blocks.
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## Caveats
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- Block-device size detection uses `BLKGETSIZE64`; the tool is Linux only.
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- If a destination path doesn't exist yet, it's created as a regular
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file — clonetool won't create device nodes, so double-check device
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paths for typos before running.
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- SSH host keys are accepted on first connect (`StrictHostKeyChecking=accept-new`)
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and rejected if they later change, same as normal SSH behavior.
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- Because every run re-hashes both sides in full, a re-sync costs a full
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read of source and destination even when little changed — the win is in
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the bytes transferred, not the bytes read. The two reads run in
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parallel; the status line shows a trailing `scan H/M` until the
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destination fingerprint catches up.
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- `agent` is an internal subcommand spawned automatically by `sync`; it's
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not meant to be run by hand, though it will work standalone for
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debugging.
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