A user-configurable login shell wrapper.
Crash is a super lightweight shim that executes the shells that are seperated by :
in your SHELLS environment variable in order, halting execution if one exits
sucessfully (with a 0 exit code).
If you don't have anything in your SHELLS environment variable or all the ones
that did exist failed to launch, Crash will use the fallback shell that is
configured at compile time (by default, this is bashInteractive from nixpkgs,
however you can change this by overriding the fallbackShell call option).
- To allow users to configure their own shells without superuser access (You can
set the
SHELLSvariable to something like.config/shelland let users change that file). - To be able to hotswap between shells when using SSH. This is even more useful if multiple people who use the same user account on a machine use different shells. See the "Tips & Tricks" section.
- To have a fallback shell in case your primary one, which is your login shell, breaks and you don't want to get locked out (especially useful when using new unstable shells like Nushell).
Simply add this repository to your inputs like so:
{
inputs.crash.url = "github:RGBCube/crash";
}And then you can set the package as your default user shell like so, in a NixOS module:
{
outputs = { nixpkgs, crash }: {
nixosConfigurations.myhostname = nixpkgs.lib.nixosSystem {
modules = [
({ pkgs, lib, ... }: {
nixpkgs.overlays = [ crash.overlays.default ];
users.defaultUserShell = pkgs.crash;
# Here we set our default shells. Nushell will be tried first, if that
# exits with an error, fish will be launched instead. And if fish fails, the
# fallback shell, which is pkgs.bashInteractive will get run.
environment.sessionVariables.SHELLS = "${lib.getExe pkgs.nushell}:${lib.getExe pkgs.fish}";
# This would also work, as Crash searches $PATH:
#
# environment.sessionVariables.SHELLS = "nu:fish";
#
# However, just setting an absolute path is pretty easy and better.
})
# Uncomment to make the fallback shell of crash pkgs.dash. Will require a recompilation!
# {
# nixpkgs.overlays = [(final: prev: {
# crash = prev.crash.override { fallbackShell = final.dash };
# })];
# }
];
};
}
}First, you have to compile the program (requires Zig 0.12.0):
zig build --release=safe -Dcpu=baseline -Dfallback_shell=/bin/<yourshell>After that, the binary should be in zig-out/bin/crash. You can copy it to
/bin like so:
cp zig-out/bin/crash /bin/After that, you will need to edit PAM settings to set the SHELLS environment
variable early on in the boot process. Consult your distros documentation on
how to do this, as it may vary.
You can control the default shell / program that will get launched
by SSH using Crash. All you need to do it make OpenSSH accept the SHELLS
environment variable and set it when SSH'ing in. Here is a NixOS
module that does that:
{
services.openssh = {
enable = true;
settings.AcceptEnv = "SHELLS";
};
}And you can utilize it by adding this to your .ssh/config:
Host myvps
# ..snip..
SetEnv SHELLS=fish:nu:bash:dashThen just SSH in like normal. This will launch you into fish, if that fails, into nu and so on...
- noshell: This was the primary source of inspiration. I decided to create this project as noshell requires a file on disk instead of an environment variable and my feature request for fallback shells got rejected.
Copyright (c) 2024-present RGBCube
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