Command Shell
A shell is a program that translates text commands (like ls, vim, reboot etc) into instructions for your computer. The default shell on NixOS is bash, but it can be easily changed.
Enable
When adding a new shell, always enable the shell system-wide, even if it's already enabled in your Home Manager configuration, otherwise it won't source the necessary files.
For example, for Zsh:
/etc/nixos/configuration.nix
programs.zsh.enable = true;
Changing the default shell
For all users
To set a command shell as the default for all users, use the defaultUserShell option.
For example, to set Zsh as the default user shell for all users:
/etc/nixos/configuration.nix
users.defaultUserShell = pkgs.zsh;
For a specific user
To set a command shell as the default for a particular user, use the <name>.shell option.
For example, to set user "myuser"'s shell to fish:
/etc/nixos/configuration.nix
users.users.myuser.shell = pkgs.fish;
You can also choose whether or not a user should use the default shell:
/etc/nixos/configuration.nix
users.users.myuser.useDefaultShell = true;