The short answer
Usually, after a check. Might hold something you care about. Look inside before removing it.
What is it?
/nix/store holds every package the Nix package manager has built or downloaded, including the ones used by older generations of your profiles. On macOS it lives on its own APFS volume, usually named “Nix Store”, and is read-only. Without regular garbage collection it often grows to tens of gigabytes.
All Nix packages and old generations. Garbage collection removes only what no profile references any more.
What happens if you delete it?
Store paths removed by garbage collection are downloaded or rebuilt again when a profile, shell or build needs them. Paths used by your current profiles are never removed.
How to remove it properly
Run nix-collect-garbage -d in Terminal: it deletes old generations of your profiles, then removes store paths nothing references any more, permanently. On multi-user or nix-darwin installs, run it with sudo too so system profiles are collected; nix-collect-garbage --delete-older-than 30d keeps recent generations.
Use the tool’s official command: nix-collect-garbage -d
Before you delete it
Never delete files in /nix/store by hand. Deleting old generations also removes the ability to roll back to them.
How MoreRoom helps
MoreRoom recognises this item and labels it “Review first”: it shows what’s inside, its size and last use, so you can decide. Nothing is removed without your say, and everything goes to the Trash first, with Undo.
When the tool is installed, MoreRoom runs its official command for you (nix-collect-garbage -d) instead of deleting files — and tells you that this step can’t be undone.
Frequently asked questions
Can I delete the Nix store (/nix/store) on Mac?
Usually, after a check. Might hold something you care about. Look inside before removing it. Store paths removed by garbage collection are downloaded or rebuilt again when a profile, shell or build needs them. Paths used by your current profiles are never removed.
Will Nix store come back after I delete it?
Yes. Store paths removed by garbage collection are downloaded or rebuilt again when a profile, shell or build needs them. Paths used by your current profiles are never removed.
How do I remove Nix store properly?
Run nix-collect-garbage -d in Terminal: it deletes old generations of your profiles, then removes store paths nothing references any more, permanently. On multi-user or nix-darwin installs, run it with sudo too so system profiles are collected; nix-collect-garbage --delete-older-than 30d keeps recent generations.