Currently, if you want to properly chroot a systemd service, you could do it using BindReadOnlyPaths=/nix/store (which is not what I'd call "properly", because the whole store is still accessible) or use a separate derivation that gathers the runtime closure of the service you want to chroot. The former is the easier method and there is also a method directly offered by systemd, called ProtectSystem, which still leaves the whole store accessible. The latter however is a bit more involved, because you need to bind-mount each store path of the runtime closure of the service you want to chroot. This can be achieved using pkgs.closureInfo and a small derivation that packs everything into a systemd unit, which later can be added to systemd.packages. That's also what I did several times[1][2] in the past. However, this process got a bit tedious, so I decided that it would be generally useful for NixOS, so this very implementation was born. Now if you want to chroot a systemd service, all you need to do is: { systemd.services.yourservice = { description = "My Shiny Service"; wantedBy = [ "multi-user.target" ]; chroot.enable = true; serviceConfig.ExecStart = "${pkgs.myservice}/bin/myservice"; }; } If more than the dependencies for the ExecStart* and ExecStop* (which btw. also includes "script" and {pre,post}Start) need to be in the chroot, it can be specified using the chroot.packages option. By default (which uses the "full-apivfs"[3] confinement mode), a user namespace is set up as well and /proc, /sys and /dev are mounted appropriately. In addition - and by default - a /bin/sh executable is provided as well, which is useful for most programs that use the system() C library call to execute commands via shell. The shell providing /bin/sh is dash instead of the default in NixOS (which is bash), because it's way more lightweight and after all we're chrooting because we want to lower the attack surface and it should be only used for "/bin/sh -c something". Prior to submitting this here, I did a first implementation of this outside[4] of nixpkgs, which duplicated the "pathSafeName" functionality from systemd-lib.nix, just because it's only a single line. However, I decided to just re-use the one from systemd here and subsequently made it available when importing systemd-lib.nix, so that the systemd-chroot implementation also benefits from fixes to that functionality (which is now a proper function). Unfortunately, we do have a few limitations as well. The first being that DynamicUser doesn't work in conjunction with tmpfs, because it already sets up a tmpfs in a different path and simply ignores the one we define. We could probably solve this by detecting it and try to bind-mount our paths to that different path whenever DynamicUser is enabled. The second limitation/issue is that RootDirectoryStartOnly doesn't work right now, because it only affects the RootDirectory option and not the individual bind mounts or our tmpfs. It would be helpful if systemd would have a way to disable specific bind mounts as well or at least have some way to ignore failures for the bind mounts/tmpfs setup. Another quirk we do have right now is that systemd tries to create a /usr directory within the chroot, which subsequently fails. Fortunately, this is just an ugly error and not a hard failure. [1]: https://github.com/headcounter/shabitica/blob/3bb01728a0237ad5e7/default.nix#L43-L62 [2]: https://github.com/aszlig/avonc/blob/dedf29e092481a33dc/nextcloud.nix#L103-L124 [3]: The reason this is called "full-apivfs" instead of just "full" is to make room for a *real* "full" confinement mode, which is more restrictive even. [4]: https://github.com/aszlig/avonc/blob/92a20bece4df54625e/systemd-chroot.nix Signed-off-by: aszlig <aszlig@nix.build> |
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doc | ||
lib | ||
maintainers | ||
nixos | ||
pkgs | ||
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.gitattributes | ||
.gitignore | ||
.version | ||
COPYING | ||
default.nix | ||
README.md |
Nixpkgs is a collection of packages for the Nix package manager. It is periodically built and tested by the Hydra build daemon as so-called channels. To get channel information via git, add nixpkgs-channels as a remote:
% git remote add channels https://github.com/NixOS/nixpkgs-channels.git
For stability and maximum binary package support, it is recommended to maintain
custom changes on top of one of the channels, e.g. nixos-18.09
for the latest
release and nixos-unstable
for the latest successful build of master:
% git remote update channels
% git rebase channels/nixos-18.09
For pull requests, please rebase onto nixpkgs master
.
NixOS Linux distribution source code is located inside
nixos/
folder.
- NixOS installation instructions
- Documentation (Nix Expression Language chapter)
- Manual (How to write packages for Nix)
- Manual (NixOS)
- Community maintained wiki
- Continuous package builds for unstable/master
- Continuous package builds for 18.09 release
- Tests for unstable/master
- Tests for 18.09 release
Communication:
Note: MIT license does not apply to the packages built by Nixpkgs, merely to the package descriptions (Nix expressions, build scripts, and so on). It also might not apply to patches included in Nixpkgs, which may be derivative works of the packages to which they apply. The aforementioned artifacts are all covered by the licenses of the respective packages.