Noshell is a simple shim that executes $XDG_CONFIG_HOME/shell as your login shell. If you configure noshell system-wide, users can configure their login shell with a simple ln -sT /path/to/zsh ~/.config/shell, instead of requiring superuser permissions to modify /etc/shells.

By default, noshell checks the following locations in the order:

• $XDG_CONFIG_HOME/shell
• $HOME/.config/shell
• pkgs.bashInteractive as the fallback. Can be configured at build-time

Add this flake's nixosModules.default to your NixOS imports, and set:

programs.noshell.enable = true

Noshell will be configured as the default shell to ALL users. You might want to disable noshell for some user as a fallback, like users.users.root.shell = pkgs.bashInteractive;.

Noshell enables some patterns in the NixOS ecosystem, such as:

• Using a shell with a configuration wrapper. As the wrapper is a different program that is not present in /etc/shells. See https://github.com/viperML/wrapper-manager.
• User-level configuration of the login shell with home-manager (xdg.configFile."shell".source = lib.getExe pkgs.nushell;)

It can be useful too outside of NixOS, for example to use a custom build of some shell.

As far as I know, there is nothing "written in stone" about what a login shell must do, but other tools in Linux do expect some functionality.

Some of these assumptions are:

• The login shell is expected to . /etc/profile by its own. This file is a POSIX sh script that sets up environment variables needed by the session. pam_env also sets environment variables but that is handled earlier in the login process.
• login may call your shell with -progname, that is with a dash as the first character, to indicate that this is a login shell.
• Other programs may call your shell with the argument -l to indicate that it is a login shell.
• Some programs might assume $SHELL is something that you can pass arguments to, whatever the arguments are, with -c.

Please report any functionality expected from a login shell in the issues board: https://github.com/viperML/noshell/issues.