gcan — see what's eating your Nix store, and reclaim it

nix-collect-garbage only frees what nothing points to. The trouble is that a lot does point to things — every nix build result, every direnv environment, every old profile generation is a GC root that quietly pins its whole dependency closure on disk. Months later you run garbage collection, it frees almost nothing, and you have no idea why.

gcan answers that question. It looks at all your GC roots and shows you, sorted biggest-first, how much disk each one is really keeping alive, where it lives, and how long it's been there — so you can see what to let go of and clear it out safely.

      SIZE     AGE  ROOTS  LOCATION
     4.8GB      6d      7  /home/you/src/old-project/.direnv/  (direnv)
     3.7GB     14d     30  /home/you/src/training/.direnv/  (direnv)
     1.2GB     90d      1  /home/you/src/experiment/result-1
     741MB     21d      1  ~/.local/state/nix/profiles/profile-51-link
      ----
      26GB             TOTAL reclaimable

Why you'd want it

• "nix-collect-garbage barely freed anything." Something is pinning the store. gcan shows you exactly what, ranked by size.
• direnv pack-rats. Every project with a .direnv keeps a full copy of its flake inputs alive. A repo you haven't opened in three months can still be holding gigabytes. gcan groups all of a project's direnv roots into one line, so you see the true cost per project — not 30 cryptic hashes.
• Forgotten result links. That result symlink from a nix build you ran once is pinning its entire closure forever. gcan lists them with their age.
• Old generations. Stale profile and home-manager generations add up; gcan surfaces the big, old ones.
• Spring cleaning. Sort by age, find what you haven't touched in months, and reclaim it in one pass.

Using it

gcan has three subcommands: list (show roots), delete (remove them), and tui (do it interactively).

List the biggest reclaimable roots:

gcan list

Narrow it down to the things actually worth clearing — say, anything over 1 GB that you haven't touched in a month, oldest first:

gcan list --min-size 1G --min-age 30d --sort age

By default list only shows roots you can safely delete. Add --all to see the full picture, including the live system and other protected roots (these are marked and can never be deleted). You can also sort by size, name, or age (--sort) and flip the order with -r.

Browse and clean up interactively

gcan tui

This opens a full-screen view you can drive with the keyboard:

 ↑/↓ (or j/k)  move          s  sort by size       t  show all / only deletable
 Home/End      jump          n  sort by name       r  reverse the order
 D             delete        a  sort by age         q / Esc  quit

Press D on a root to delete it — gcan asks for confirmation, removes it, and refreshes the list on the spot. You can start it narrowed down too, e.g. gcan tui --min-size 1G.

Clean up from the command line

# Delete everything ≥2 GB and older than 30 days, after a confirmation prompt:
gcan delete --min-size 2G --min-age 30d

# Delete and reclaim the space in one go (runs nix-collect-garbage for you):
gcan delete --min-size 2G --min-age 30d --gc

# Or pipe the exact symlinks somewhere and remove them yourself:
gcan list --min-size 1G --format paths | xargs rm

One important last step

Deleting a root just removes the link that was pinning the data — it tells Nix the data is no longer wanted. To actually give the disk space back, run garbage collection afterwards:

nix-collect-garbage

(or pass --gc to gcan delete to have it run for you).

Safe by default

gcan will never offer to delete something that would break your system:

• It only lists roots you own and can remove — never root-owned system roots.
• The live system, the booted system, and your current home-manager generation (and anything else marked current-* / booted-*) are always protected.
• Deletions in the TUI and via gcan delete ask for confirmation first.

You can also export the full inventory as JSON (gcan list --all --format json) to feed into your own scripts or dashboards.

Maintainers

gcan is built and maintained by applicative.systems.