doc: update docs in ociTools, follow doc conventions
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Silvan Mosberger
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# pkgs.ociTools {#sec-pkgs-ociTools}
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`pkgs.ociTools` is a set of functions for creating containers according to the [OCI container specification v1.0.0](https://github.com/opencontainers/runtime-spec). Beyond that, it makes no assumptions about the container runner you choose to use to run the created container.
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`pkgs.ociTools` is a set of functions for creating runtime container bundles according to the [OCI runtime specification v1.0.0](https://github.com/opencontainers/runtime-spec/blob/v1.0.0/spec.md).
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It makes no assumptions about the container runner you choose to use to run the created container.
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The set of functions in `pkgs.ociTools` currently does not handle the [OCI image specification](https://github.com/opencontainers/image-spec).
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At a high-level an OCI implementation would download an OCI Image then unpack that image into an OCI Runtime filesystem bundle.
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At this point the OCI Runtime Bundle would be run by an OCI Runtime.
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`pkgs.ociTools` provides utilities to create OCI Runtime bundles.
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## buildContainer {#ssec-pkgs-ociTools-buildContainer}
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This function creates a simple OCI container that runs a single command inside of it. An OCI container consists of a `config.json` and a rootfs directory. The nix store of the container will contain all referenced dependencies of the given command.
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This function creates an OCI runtime container (consisting of a `config.json` and a root filesystem directory) that runs a single command inside of it.
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The nix store of the container will contain all referenced dependencies of the given command.
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The parameters of `buildContainer` with an example value are described below:
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This function has an assumption that the container will run on POSIX platforms, and sets configurations (such as the user running the process or certain mounts) according to this assumption.
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Because of this, a container built with `buildContainer` will not work on Windows or other non-POSIX platforms without modifications to the container configuration.
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These modifications aren't supported by `buildContainer`.
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For `linux` platforms, `buildContainer` also configures the following namespaces (see {manpage}`unshare(1)`) to isolate the OCI container from the global namespace:
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PID, network, mount, IPC, and UTS.
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Note that no user namespace is created, which means that you won't be able to run the container unless you are the `root` user.
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### Inputs {#ssec-pkgs-ociTools-buildContainer-inputs}
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`buildContainer` expects an argument with the following attributes:
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`args` (List of String)
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: Specifies a set of arguments to run inside the container.
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Any packages referenced by `args` will be made available inside the container.
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`mounts` (Attribute Set; _optional_)
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: Would specify additional mounts that the runtime must make available to the container.
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:::{.warning}
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As explained in [issue #290879](https://github.com/NixOS/nixpkgs/issues/290879), this attribute is currently ignored.
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:::
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:::{.note}
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`buildContainer` includes a minimal set of necessary filesystems to be mounted into the container, and this set can't be changed with the `mounts` attribute.
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:::
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_Default value:_ `{}`.
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`readonly` (Boolean; _optional_)
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: If `true`, sets the container's root filesystem as read-only.
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_Default value:_ `false`.
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`os` **DEPRECATED**
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: Specifies the operating system on which the container filesystem is based on.
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If specified, its value should follow the [OCI Image Configuration Specification](https://github.com/opencontainers/image-spec/blob/main/config.md#properties).
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According to the linked specification, all possible values for `$GOOS` in [the Go docs](https://go.dev/doc/install/source#environment) should be valid, but will commonly be one of `darwin` or `linux`.
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_Default value:_ `"linux"`.
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`arch` **DEPRECATED**
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: Used to specify the architecture for which the binaries in the container filesystem have been compiled.
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If specified, its value should follow the [OCI Image Configuration Specification](https://github.com/opencontainers/image-spec/blob/main/config.md#properties).
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According to the linked specification, all possible values for `$GOARCH` in [the Go docs](https://go.dev/doc/install/source#environment) should be valid, but will commonly be one of `386`, `amd64`, `arm`, or `arm64`.
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_Default value:_ `x86_64`.
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### Examples {#ssec-pkgs-ociTools-buildContainer-examples}
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::: {.example #ex-ociTools-buildContainer-bash}
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# Creating an OCI runtime container that runs `bash`
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This example uses `ociTools.buildContainer` to create a simple container that runs `bash`.
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```nix
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buildContainer {
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{ ociTools, lib, bash }:
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ociTools.buildContainer {
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args = [
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(with pkgs;
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writeScript "run.sh" ''
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#!${bash}/bin/bash
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exec ${bash}/bin/bash
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'').outPath
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(lib.getExe bash)
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];
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mounts = {
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"/data" = {
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type = "none";
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source = "/var/lib/mydata";
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options = [ "bind" ];
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};
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};
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readonly = false;
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}
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```
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- `args` specifies a set of arguments to run inside the container. This is the only required argument for `buildContainer`. All referenced packages inside the derivation will be made available inside the container.
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As an example of how to run the container generated by this package, we'll use `runc` to start the container.
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Any other tool that supports OCI containers could be used instead.
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- `mounts` specifies additional mount points chosen by the user. By default only a minimal set of necessary filesystems are mounted into the container (e.g procfs, cgroupfs)
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```shell
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$ nix-build
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(some output removed for clarity)
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/nix/store/7f9hgx0arvhzp2a3qphp28rxbn748l25-join
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- `readonly` makes the container's rootfs read-only if it is set to true. The default value is false `false`.
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$ cd /nix/store/7f9hgx0arvhzp2a3qphp28rxbn748l25-join
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$ nix-shell -p runc
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[nix-shell:/nix/store/7f9hgx0arvhzp2a3qphp28rxbn748l25-join]$ sudo runc run ocitools-example
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help
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GNU bash, version 5.2.26(1)-release (x86_64-pc-linux-gnu)
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(some output removed for clarity)
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```
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:::
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@ -318,5 +318,6 @@
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"passwd(5)": "https://man.archlinux.org/man/passwd.5",
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"group(5)": "https://man.archlinux.org/man/group.5",
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"login.defs(5)": "https://man.archlinux.org/man/login.defs.5",
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"unshare(1)": "https://man.archlinux.org/man/unshare.1.en",
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"nix-shell(1)": "https://nixos.org/manual/nix/stable/command-ref/nix-shell.html"
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}
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