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+# lethe
+
+> Never forget your NixOS deployments.
+
+`lethe` records snapshots of NixOS systems. It captures your system's full
+closure into a local SQLite database, so you can list, inspect, and diff them
+later. This can be useful when looking into past deployments to try and
+identify when an issue may first have arise.
+
+Named after the river of oblivion, but it does the opposite.
+
+## Usage
+
+Record the current local system:
+
+```sh
+lethe record --local
+```
+
+Record a remote machine over SSH:
+
+```sh
+lethe record root@my-server
+lethe record ssh://my-server:2222
+```
+
+By default `lethe` records `/run/current-system`. However, you can pass
+`--system-link` to record something else. For example, `/run/booted-system`, or a specific
+generation like `/nix/var/nix/profiles/system-626-link`, or any `/nix/store` path.
+
+List what you've recorded:
+
+```sh
+lethe machines              # all known machines
+lethe deployments my-server # deployments for one machine
+lethe show 42               # details of a single deployment
+lethe diff 41 42            # diff two deployments (closure + size delta)
+lethe diff 41               # diff against the latest deployment of the same machine
+```
+
+## Data Storage
+
+The database lives at `$XDG_DATA_HOME/lethe/lethe.db` (typically
+`~/.local/share/lethe/lethe.db`). You can change this with `--db <path>` or the
+`LETHE_DB` environment variable.
+
+## A little lore
+
+`lethe` is named after [Lethe](https://en.wikipedia.org/wiki/Lethe) one of the
+rivers to the underworld from Greek mythology. The word means "forgetting" or
+"forgetfulness", which makes the name antithesis.