78 lines
3.2 KiB
Markdown
78 lines
3.2 KiB
Markdown
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# fakeNss {#sec-fakeNss}
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Provides `/etc/passwd` and `/etc/group` files that contain `root` and `nobody`, allowing user/group lookups to work in binaries that insist on doing those.
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This might be a better choice than a custom script running `useradd` and related utilities if you only need those files to exist with some entries.
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`fakeNss` also provides `/etc/nsswitch.conf`, configuring NSS host resolution to first check `/etc/hosts` before checking DNS, since the default in the absence of a config file (`dns [!UNAVAIL=return] files`) is quite unexpected.
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It also creates an empty directory at `/var/empty` because it uses that as the home directory for the `root` and `nobody` users.
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The `/var/empty` directory can also be used as a `chroot` target to prevent file access in processes that do not need to access files, if your container runs such processes.
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The user entries created by `fakeNss` use the `/bin/sh` shell, which is not provided by `fakeNss` because in most cases it won't be used.
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If you need that to be available, see [`dockerTools.binSh`](#sssec-pkgs-dockerTools-helpers-binSh) or provide your own.
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## Inputs {#sec-fakeNss-inputs}
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`fakeNss` is made available in Nixpkgs as a package rather than a function, but it has two attributes that can be overridden and might be useful in particular cases.
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For more details on how overriding works, see [](#ex-fakeNss-overriding) and [](#sec-pkg-override).
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`extraPasswdLines` (List of Strings; _optional_)
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: A list of lines that will be added to `/etc/passwd`.
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Useful if extra users need to exist in the output of `fakeNss`.
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If `extraPasswdLines` is specified, it will **not** override the `root` and `nobody` entries created by `fakeNss`.
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Those entries will always exist.
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Lines specified here must follow the format in {manpage}`passwd(5)`.
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_Default value:_ `[]`.
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`extraGroupLines` (List of Strings; _optional_)
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: A list of lines that will be added to `/etc/group`.
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Useful if extra groups need to exist in the output of `fakeNss`.
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If `extraGroupLines` is specified, it will **not** override the `root` and `nobody` entries created by `fakeNss`.
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Those entries will always exist.
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Lines specified here must follow the format in {manpage}`group(5)`.
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_Default value:_ `[]`.
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## Examples {#sec-fakeNss-examples}
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:::{.example #ex-fakeNss-dockerTools-buildImage}
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# Using `fakeNss` with `dockerTools.buildImage`
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This example shows how to use `fakeNss` as-is.
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It is useful with functions in `dockerTools` to allow building Docker images that have the `/etc/passwd` and `/etc/group` files.
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This example includes the `hello` binary in the image so it can do something besides just have the extra files.
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```nix
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{ dockerTools, fakeNss, hello }:
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dockerTools.buildImage {
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name = "image-with-passwd";
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tag = "latest";
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copyToRoot = [ fakeNss hello ];
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config = {
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Cmd = [ "/bin/hello" ];
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};
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}
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```
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:::
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:::{.example #ex-fakeNss-overriding}
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# Using `fakeNss` with an override to add extra lines
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The following code uses `override` to add extra lines to `/etc/passwd` and `/etc/group` to create another user and group entry.
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```nix
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{ fakeNss }:
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fakeNss.override {
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extraPasswdLines = ["newuser:x:9001:9001:new user:/var/empty:/bin/sh"];
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extraGroupLines = ["newuser:x:9001:"];
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}
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```
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:::
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