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:

lethe record --local

Record a remote machine over SSH:

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:

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
lethe diff my-server        # diff the last two deployments for a machine
lethe diff /nix/store/...-nixos-system-foo 42  # ids and toplevel paths are interchangeable

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 one of the rivers to the underworld from Greek mythology. The word means "forgetting" or "forgetfulness", which makes the name antithesis.