lix/src/nix/profile.md

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Description

nix profile allows you to create and manage Nix profiles. A Nix profile is a set of packages that can be installed and upgraded independently from each other. Nix profiles are versioned, allowing them to be rolled back easily.

Default profile

The default profile used by nix profile is $HOME/.nix-profile, which, if it does not exist, is created as a symlink to /nix/var/nix/profiles/per-user/default if Nix is invoked by the root user, or /nix/var/nix/profiles/per-user/username otherwise.

You can specify another profile location using --profile path.

Filesystem layout

Profiles are versioned as follows. When using profile path, path is a symlink to path-N, where N is the current version of the profile. In turn, path-N is a symlink to a path in the Nix store. For example:

$ ls -l /nix/var/nix/profiles/per-user/alice/profile*
lrwxrwxrwx 1 alice users 14 Nov 25 14:35 /nix/var/nix/profiles/per-user/alice/profile -> profile-7-link
lrwxrwxrwx 1 alice users 51 Oct 28 16:18 /nix/var/nix/profiles/per-user/alice/profile-5-link -> /nix/store/q69xad13ghpf7ir87h0b2gd28lafjj1j-profile
lrwxrwxrwx 1 alice users 51 Oct 29 13:20 /nix/var/nix/profiles/per-user/alice/profile-6-link -> /nix/store/6bvhpysd7vwz7k3b0pndn7ifi5xr32dg-profile
lrwxrwxrwx 1 alice users 51 Nov 25 14:35 /nix/var/nix/profiles/per-user/alice/profile-7-link -> /nix/store/mp0x6xnsg0b8qhswy6riqvimai4gm677-profile

Each of these symlinks is a root for the Nix garbage collector.

The contents of the store path corresponding to each version of the profile is a tree of symlinks to the files of the installed packages, e.g.

$ ll -R /nix/var/nix/profiles/per-user/eelco/profile-7-link/
/nix/var/nix/profiles/per-user/eelco/profile-7-link/:
total 20
dr-xr-xr-x 2 root root 4096 Jan  1  1970 bin
-r--r--r-- 2 root root 1402 Jan  1  1970 manifest.json
dr-xr-xr-x 4 root root 4096 Jan  1  1970 share

/nix/var/nix/profiles/per-user/eelco/profile-7-link/bin:
total 20
lrwxrwxrwx 5 root root 79 Jan  1  1970 chromium -> /nix/store/ijm5k0zqisvkdwjkc77mb9qzb35xfi4m-chromium-86.0.4240.111/bin/chromium
lrwxrwxrwx 7 root root 87 Jan  1  1970 spotify -> /nix/store/w9182874m1bl56smps3m5zjj36jhp3rn-spotify-1.1.26.501.gbe11e53b-15/bin/spotify
lrwxrwxrwx 3 root root 79 Jan  1  1970 zoom-us -> /nix/store/wbhg2ga8f3h87s9h5k0slxk0m81m4cxl-zoom-us-5.3.469451.0927/bin/zoom-us

/nix/var/nix/profiles/per-user/eelco/profile-7-link/share/applications:
total 12
lrwxrwxrwx 4 root root 120 Jan  1  1970 chromium-browser.desktop -> /nix/store/4cf803y4vzfm3gyk3vzhzb2327v0kl8a-chromium-unwrapped-86.0.4240.111/share/applications/chromium-browser.desktop
lrwxrwxrwx 7 root root 110 Jan  1  1970 spotify.desktop -> /nix/store/w9182874m1bl56smps3m5zjj36jhp3rn-spotify-1.1.26.501.gbe11e53b-15/share/applications/spotify.desktop
lrwxrwxrwx 3 root root 107 Jan  1  1970 us.zoom.Zoom.desktop -> /nix/store/wbhg2ga8f3h87s9h5k0slxk0m81m4cxl-zoom-us-5.3.469451.0927/share/applications/us.zoom.Zoom.desktop

…

The file manifest.json records the provenance of the packages that are installed in this version of the profile. It looks like this:

{
  "version": 1,
  "elements": [
    {
      "active": true,
      "attrPath": "legacyPackages.x86_64-linux.zoom-us",
      "originalUrl": "flake:nixpkgs",
      "storePaths": [
        "/nix/store/wbhg2ga8f3h87s9h5k0slxk0m81m4cxl-zoom-us-5.3.469451.0927"
      ],
      "uri": "github:NixOS/nixpkgs/13d0c311e3ae923a00f734b43fd1d35b47d8943a"
    },
    …
  ]
}

Each object in the array elements denotes an installed package and has the following fields:

• originalUrl: The flake reference specified by the user at the time of installation (e.g. nixpkgs). This is also the flake reference that will be used by nix profile upgrade.

• uri: The immutable flake reference to which originalUrl resolved.

• attrPath: The flake output attribute that provided this package. Note that this is not necessarily the attribute that the user specified, but the one resulting from applying the default attribute paths and prefixes; for instance, hello might resolve to packages.x86_64-linux.hello and the empty string to packages.x86_64-linux.default.

• storePath: The paths in the Nix store containing the package.

• active: Whether the profile contains symlinks to the files of this package. If set to false, the package is kept in the Nix store, but is not "visible" in the profile's symlink tree.

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