How to upgrade packages

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Had the same question so putting it here too in case it helps:

TL;DR

  1. Are you on the latest channel?
    (See how to check and set below.)

  2. sudo nix-channel --update

  3. a. (declarative/NixOS) sudo nixos-rebuild switch
    b.                   (ad-hoc) nix-env -u '*'
    c.     (Home Manager) home-manager switch (I think)

These steps should work regardless of using NixOS or not.

NOTE: Don’t know how flakes work, but it’s a fairly good bet that this won’t work with them.

Step 0. Check and set the latest channel

Step 1.'s nix-channel --update will only pull the changes in the channel that is currently set! To check the current one you are subscribed to, issue

sudo nix-channel --list

The latest NixOS manual’s Chapter 4. Upgrading NixOS will always show the name and the link of the latest channel. The Nix Channel Status page is also a very good resource.

For example, I was subscribed to channel 20.09 so I needed to update it to 21.11 by doing

$ sudo nix-channel --list
nixos https://nixos.org/channels/nixos-20.09

$ sudo nix-channel --remove nixos
$ sudo nix-channel --add https://nixos.org/channels/nixos-21.11 nixos

More info:

  • The Nix manual’s 4.4 Channels section is a short intro to Nix channels.

  • The NixOS wiki’s Nix channels article goes more into the details and has a good summary on the basic commands. (Personally, I found this one more useful.)

Step 1. Update the channel

This is required both for declarative and “ad-hoc” [sic] setups3:

sudo nix-channel --update

Even though the Nix manual has a 4.1 Basic Package Management section, it is best documented in the NixOS manual (see Chapter 7. Package Management). (Albeit, I didn’t find it straightforward figuring out the correct order of steps from these; the biggest help was this NixOS discourse thread.)

Home Manager does not seem to complicate this process. (At least, I’m using it on NixOS, and nixos-rebuild switch always takes care of everything with my setup.)

TIP FOR NIXOS USERS
The nixos-rebuild switch --upgrade combines Step 1. and Step 2. as it “is equivalent to the more verbose nix-channel --update nixos; nixos-rebuild switch”.

Step 2. Update the packages

The two adjectives, “ad-hoc” [sic] and “declarative”, are introduced in the NixOS manual to differentiate the two modes of Nix package management3:

  • “ad-hoc”: Managing packages with nix-env.1

  • “declarative”: In the NixOS manual, this refers to declaring packages as a list in NixOS’ configuration.nix, but it can be done in many other ways2.

The commands:

a. To update all packages declared in NixOS’ configuration.nix, use:

sudo nixos-rebuild switch

b. To update all packages installed with nix-env:

nix-env -u '*'

c. To update all packages installed using Home Manager:

home-manager switch

(I think. Again, I’m using Home Manager in NixOS, and never had to touch any Home Manager commands. See Home-manager equivalent of “apt upgrade”)

Footnotes

[1]: As far as I know, the NixOS manual is the only official document that uses the term “ad-hoc [sic] package management” and only to mean package management using nix-env.

(Therefore I find the term misleading, because using packages via nix-shell -p commands or custom shell.nix-es are also ad hoc forms of package management. Also, nix-env can be messy.)

[2]: For example with Home Manager, using shell.nix-es, flakes. (It is probably incorrect to list flakes, as it is a mechanism that can be used with Home Manager and nix-shell Nix expressions…)

[3]: Not sure if there is a consensus what “ad-hoc”, “declarative”, and “imperative” package management means in Nix; footnote 1 has my thoughts about “ad-hoc”, some say that using channels is always an imperative form of package management, so “declarative” seems to be overloaded…

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