HowTo: use dash as default shell, fix error "SHELL not defined in /etc/shells"

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1

Intro

dash is a pretty old but still more minimal shell. It is an alternative to bash.

It is purely POSIX-compliant, while bash uses some extra functions and syntax (“bashisms”) which break when using dash.

Dash can offer some security benefits due to being more minimal, and script execution is way faster.

Issues

When just setting the default shell to dash, the entry in /etc/shells is missing (unlike with zsh or fish).

Programs like input-remapper will not launch because of that.

Solution

Here are all config lines you need to use dash

# dash instead of bash
users = {
    defaultUserShell = pkgs.dash;
    users.root.shell = pkgs.dash;
};

# fix the mentioned issue
environment.shells = with pkgs; [
    dash
];

# do this for all configured users
users.users.user = {
    ...
    useDefaultShell = true;
};
2

This is controlled by environment.shells.

users.defaultUserShell should be enough, users.users.root.shell defaults to it:

As does every user that has isNormalUser:

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3

A general word of advise:

dash is meant as a shell script interpreter more than a login shell. While the usage as a primary login shell is not discouraged by upstream, remember that it is not the primary usecase either.

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