pyrox.dev
1# Cleaning the Nix Store {#sec-nix-gc}
2
3Nix has a purely functional model, meaning that packages are never
4upgraded in place. Instead new versions of packages end up in a
5different location in the Nix store (`/nix/store`). You should
6periodically run Nix's *garbage collector* to remove old, unreferenced
7packages. This is easy:
8
9```ShellSession
10$ nix-collect-garbage
11```
12
13Alternatively, you can use a systemd unit that does the same in the
14background:
15
16```ShellSession
17# systemctl start nix-gc.service
18```
19
20You can tell NixOS in `configuration.nix` to run this unit automatically
21at certain points in time, for instance, every night at 03:15:
22
23```nix
24nix.gc.automatic = true;
25nix.gc.dates = "03:15";
26```
27
28The commands above do not remove garbage collector roots, such as old
29system configurations. Thus they do not remove the ability to roll back
30to previous configurations. The following command deletes old roots,
31removing the ability to roll back to them:
32
33```ShellSession
34$ nix-collect-garbage -d
35```
36
37You can also do this for specific profiles, e.g.
38
39```ShellSession
40$ nix-env -p /nix/var/nix/profiles/per-user/eelco/profile --delete-generations old
41```
42
43Note that NixOS system configurations are stored in the profile
44`/nix/var/nix/profiles/system`.
45
46Another way to reclaim disk space (often as much as 40% of the size of
47the Nix store) is to run Nix's store optimiser, which seeks out
48identical files in the store and replaces them with hard links to a
49single copy.
50
51```ShellSession
52$ nix-store --optimise
53```
54
55Since this command needs to read the entire Nix store, it can take quite
56a while to finish.
57
58## NixOS Boot Entries {#sect-nixos-gc-boot-entries}
59
60If your `/boot` partition runs out of space, after clearing old profiles
61you must rebuild your system with `nixos-rebuild boot` or `nixos-rebuild
62switch` to update the `/boot` partition and clear space.