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README.md+31−48 c+11−43 flake.nix+47−96

README.md+31−48

@@ -5,10 +5,8 @@ A Nix flake that builds an **OCI image** (via

55Apple's [`container`](https://github.com/apple/container) CLI on macOS.

77It's a plain, single-process image — no NixOS, no systemd — defined in

8−[`flake.nix`](./flake.nix). `c start` drops you into a

9−[`herdr`](https://herdr.dev) session whose panes use your host login shell

10−(detected and bundled by `c init`). You choose what else it ships via a

11−per-project `container.nix`.

8+[`flake.nix`](./flake.nix). It runs `fish` by default; you choose what it ships

9+via a per-project `container.nix`.

1210

1311## Prerequisites

1412

@@ -16,43 +14,32 @@ per-project `container.nix`.

1614- Apple's [`container`](https://github.com/apple/container) CLI installed, with

1715 services started: `container system start` (first run downloads a Linux

1816 kernel).

19−- A **Linux builder** *only if you use packages that aren't in the binary

20− cache*. The image is assembled entirely on macOS — the root filesystem is just

21− a host-built symlink tree over the **substituted** Linux store paths — so a

22− fully-cached package set needs no builder. Compiling a Linux package that

23− `cache.nixos.org` doesn't have does, though: use a [remote builder][builders]

24− or, on Apple Silicon, the `nix-darwin` `linux-builder`.

17+- A **Linux builder** — the image *contents* are Linux binaries, which can't be

18+ built on macOS. Use a [remote builder][builders] or, on Apple Silicon, the

19+ `nix-darwin` `linux-builder`. With one configured, `nix` dispatches Linux

20+ builds to it automatically (most packages also come prebuilt from the binary

21+ cache, so the builder is only needed for the uncached bits).

2522

2623[builders]: https://nix.dev/manual/nix/latest/advanced-topics/distributed-builds

2724

2825## Packages

2926

30−`init` builds the image from a **`container.nix`** in the current directory — an

31−attrset with a `packages` function (`{ pkgs, nur }` returning the package list;

32−`nur` is [NUR](https://github.com/nix-community/NUR), for packages outside

33−nixpkgs) and an optional `mounts` list. It is **required**; there is no default.

27+`init` builds the image from a **`container.nix`** in the current directory — a

28+`{ pkgs, nur }` function returning the package list (`nur` is

29+[NUR](https://github.com/nix-community/NUR), for packages outside nixpkgs). It

30+is **required**; there is no default set.

3431

3532```nix

3633# ./container.nix

37−{

38− packages = { pkgs, nur }: with pkgs; [

39− git

40− go

41− nur.repos.charmbracelet.crush

42− ];

43− # Extra "host:container" bind mounts, on top of $PWD → /workspace. A leading

44− # ~/ in the host path expands to $HOME. Optional.

45− mounts = [

46− "~/data:/data"

47− ];

48−}

34+{ pkgs, nur }: with pkgs; [

35+ fish # the default cmd is /bin/fish, so include it (or change config.cmd)

36+ coreutils

37+ git

38+ go

39+ nur.repos.charmbracelet.crush

40+]

4941```

5042

51−Your **host login shell** (detected by `c init`, bash fallback), **coreutils**,

52−[**herdr**](https://herdr.dev) (the session `c start` launches), **Nix** itself

53−(with CA certs and `nix-command`/`flakes` enabled, single-user), and the ncurses

54−**terminfo** database are always included — no need to list them.

55−

5643Point at a different file with `-c`/`--config`:

5744

5845```sh

@@ -68,17 +55,17 @@ that holds a `container.nix`; the container is named after that directory.

6855# build the image, load it, and create the container (named after $PWD):

6956nix run github:ilyakooo0/nix-container -- init

7057

71−# start it and attach — drops you into a herdr session:

58+# start it and attach — drops you into fish:

7259nix run github:ilyakooo0/nix-container -- start

7360```

7461

7562- `init` builds the OCI archive in a temp dir, loads it into `container`,

7663 deletes the temp file, then (re)creates the container. It mounts the current

77− directory at `/workspace` (the container's working directory).

64+ directory at `/workspace` (the container's working directory) and your

65+ `~/.config` at `/root/.config`.

7866- `--ssh` forwards your host SSH agent socket into the container (so `git` over

7967 SSH works with your keys).

80−- Add more mounts persistently via `mounts` in `container.nix` (above), or

81− ad-hoc by passing them through to `create` (mounts can only be set at creation):

68+- Add more mounts by passing them through (mounts can only be set at creation):

8269

8370 ```sh

8471 nix run github:ilyakooo0/nix-container -- init -v $HOME/data:/data

@@ -99,19 +86,18 @@ nix run github:ilyakooo0/nix-container -- init

9986## Customize further

10087

10188Fork or clone to change what isn't per-project — `config.cmd`/`env` or the image

102−name — in [`flake.nix`](./flake.nix). The flake also exposes build helpers:

89+name — in [`flake.nix`](./flake.nix). The flake also exposes build helpers, both

90+taking a `{ pkgs, nur }: [ ... ]` function:

10391

104−- `lib.<system>.copyWith` → a skopeo copy app for a `{ pkgs, nur }: [ ... ]`

105− function, for building/pushing the image anywhere skopeo can write (e.g. a

106− registry):

92+- `lib.<system>.mkImage` → an OCI image.

93+- `lib.<system>.copyWith` → a skopeo copy app, for building/pushing the image

94+ anywhere skopeo can write (e.g. a registry):

10795

10896 ```sh

10997 drv=$(nix build --no-link --print-out-paths --impure --expr \

110− '(builtins.getFlake "github:ilyakooo0/nix-container").lib.${builtins.currentSystem}.copyWith (import ./container.nix).packages')

98+ '(builtins.getFlake "github:ilyakooo0/nix-container").lib.${builtins.currentSystem}.copyWith (import ./container.nix)')

11199 $drv/bin/copy-to docker://ghcr.io/me/img:latest

112100 ```

113−- `lib.<system>.mkImage <name> <shell>` → the underlying OCI image (`copyWith`

114− defaults these to `nix-container` / `bash`).

115101

116102The flake uses `flake-utils` over `{aarch64,x86_64}-{darwin,linux}`; the host

117103system maps to the matching Linux target automatically (an Intel Mac builds an

@@ -119,12 +105,9 @@ system maps to the matching Linux target automatically (an Intel Mac builds an

119105

120106## How it works

121107

122−- **Contents** are Linux store paths — downloaded prebuilt from the binary cache

123− (only built on a Linux builder if not cached).

124−- **Assembly** runs entirely on your Mac: `copyToRoot` is a *host-arch* `buildEnv`

125− symlink tree over those Linux paths (symlinks are arch-neutral), and

126− `nix2container` + `skopeo` package it — so for a cached set, `init` produces a

127− loadable Linux image with no Linux build at all.

108+- **Contents** are built from `pkgsLinux` → the Linux builder.

109+- **Assembly** (`nix2container` + the `skopeo` copy) runs on your Mac, so a

110+ single `init` produces a loadable archive.

128111- Apple's `container` runs each container in its own lightweight Linux VM and

129112 consumes standard OCI images — no `--privileged` or systemd needed.

130113

c+11−43

@@ -1,7 +1,7 @@

11#!/usr/bin/env fish

22# Manage a container named after the current directory.

33# c init [-c FILE] [extra create args] build + load the image, then (re)create it

4−# (config from FILE, default ./container.nix)

4+# (packages from FILE, default ./container.nix)

55# c start start it and attach

77set -l name (path basename $PWD)

@@ -22,23 +22,17 @@ switch $argv[1]

2222 end

2323

2424 if not test -e $config

25− echo "c: config file not found: $config" >&2

26− echo " create one ('{ packages = { pkgs, nur }: [ ... ]; mounts = [ ]; }') or pass -c FILE" >&2

25+ echo "c: package file not found: $config" >&2

26+ echo " create one ('{ pkgs, nur }: [ ... ]') or pass -c FILE" >&2

2727 exit 1

2828 end

2929

30− # Host login shell (by name): added to the image automatically and baked

31− # in as the cmd + default $SHELL (what herdr panes etc. spawn), so it

32− # needn't be listed in container.nix. Falls back to bash.

33− set -l shell bash

34− test -n "$SHELL"; and set shell (path basename $SHELL)

35−

36− # Build an image with the config's `packages` (plus the shell) into a

37− # temp dir, load it, then clean up.

30+ # Build an image with exactly the packages from $config, into a temp

31+ # dir, load it, then clean up.

3832 set -l tmp (mktemp -d)

3933 set -l archive $tmp/image.tar.gz

40− set -lx NIX_CONTAINER_CONFIG (path resolve $config)

41− set -l expr "(builtins.getFlake \"$flake\").lib.\${builtins.currentSystem}.copyWithShell \"nix-container-$name\" \"$shell\" (import (/. + builtins.getEnv \"NIX_CONTAINER_CONFIG\")).packages"

34+ set -lx NIX_CONTAINER_PKGS (path resolve $config)

35+ set -l expr "(builtins.getFlake \"$flake\").lib.\${builtins.currentSystem}.copyWith (import (/. + builtins.getEnv \"NIX_CONTAINER_PKGS\"))"

4236 set -l copyer (nix build --impure --no-link --print-out-paths --expr "$expr")

4337 set -l rc $status

4438 if test $rc -eq 0

@@ -53,40 +47,14 @@ switch $argv[1]

5347 rm -rf $tmp

5448 test $rc -eq 0; or exit $rc

5549

56− # Mount the project at /workspace (the default cwd), plus any extra

57− # mounts from the config (`mounts = [ "host:container" … ]`). A leading

58− # ~/ in the host path expands to $HOME (nix leaves it literal).

50+ # Mount the project at /workspace (the default cwd) and host ~/.config.

5951 set -l mounts -v "$PWD:/workspace"

60− for m in (nix eval --impure --raw --expr "builtins.concatStringsSep \"\n\" ((import (/. + builtins.getEnv \"NIX_CONTAINER_CONFIG\")).mounts or [])")

61− set -a mounts -v (string replace -r '^~/' "$HOME/" -- $m)

62− end

63−

64− # TERM to bake into the container env (`-e TERM`): the runtime hands the

65− # `start -ai` session a bare "xterm", so set the host's real terminal,

66− # mapped to an entry the bundled ncurses ships — Ghostty reports

67− # "xterm-ghostty", which ncurses ships as "ghostty" — falling back to

68− # xterm-256color for an empty or bare-"xterm" value.

69− set -l term xterm-256color

70− if test "$TERM" = xterm-ghostty

71− set term ghostty

72− else if test -n "$TERM"; and test "$TERM" != xterm

73− set term $TERM

74− end

52+ test -d $HOME/.config; and set -a mounts -v "$HOME/.config:/root/.config"

7553

76− # Replace any existing container of the same name, then create it running

77− # herdr in a session named after the project (`<dir>-container`). This

78− # overrides the image's default plain-herdr cmd; `c start` attaches to it.

54+ # Replace any existing container of the same name.

7955 container rm --force $name 2>/dev/null

80− # The image only lays down /bin and /etc, so /tmp and /run don't exist;

81− # without them anything that writes temp files (herdr, build tools, …)

82− # fails with ENOENT. Mount writable tmpfs at both.

83− container create --name $name --ssh -it -e "TERM=$term" \

84− --tmpfs /tmp --tmpfs /run --memory 8g --cwd /workspace $mounts $argv \

85− $image /bin/herdr session attach "$name-container"

56+ container create --name $name --ssh -it --cwd /workspace $mounts $argv $image

8657 case start

87− # Start the container and attach to its cmd (herdr). TERM was baked into

88− # the container env at create time (`-e TERM`), which survives this path.

89− # Exiting herdr (PID1) stops the container; `c start` boots it again.

9058 container start -ai $name

9159 case '*'

9260 echo "usage: c init [-c FILE] [create args] | start" >&2

flake.nix+47−96

@@ -72,99 +72,57 @@

7272 # Host package set, for the wrapper app below.

7373 pkgsHost = nixpkgs.legacyPackages.${system};

7474

75− # Default image name (for `copyWith`); `c init` passes a per-directory

76− # name (`nix-container-<dir>`) to `copyWithShell` instead.

75+ # Name/tag baked into the image's OCI config.

7776 imageName = "nix-container";

7877 imageTag = "latest";

7978

80− # Build the OCI image (named `name`) from a `{ pkgs, nur }: [ ... ]`

81− # package function, for the named shell. The image's `cmd` is herdr

82− # (the session `c start` attaches to); the shell is the default `$SHELL`

83− # (what herdr panes spawn) and is added automatically, so `container.nix`

84− # lists only your extras. Nix (+ CA certs) and the ncurses terminfo

85− # database are always shipped too. Nothing here is fish-specific: the

86− # TERM fixup happens host-side in `c` (passed via `-e TERM` at create).

79+ # Build the OCI image from a `{ pkgs, nur }: [ ... ]` package function.

80+ # The default `cmd` is /bin/fish, so the package set should include

81+ # `fish` (warned about below if missing) or override `config.cmd`.

8782 mkImage =

88− name: shell: packages:

89− n2c.buildImage {

90− inherit name;

91− tag = imageTag;

92− inherit arch;

93−

94− # A plain, single-process root filesystem. No NixOS, no systemd.

95− # buildEnv only *symlinks* paths (never runs them), so build it on

96− # the host arch — the tree is arch-neutral and links the

97− # (substituted) Linux store paths, sparing the Linux builder.

98− copyToRoot = pkgsHost.buildEnv {

99− name = "root";

100− paths =

101− packages {

102− pkgs = pkgsLinux;

103− nur = nurPkgs;

104− }

105− # The shell (cmd + $SHELL), when it exists in nixpkgs.

106− ++ pkgsLinux.lib.optional (pkgsLinux ? ${shell}) pkgsLinux.${shell}

107− ++ [

108− pkgsLinux.nix

109− pkgsLinux.cacert

110− # Basic userland (ls, cat, cp, sleep, …) so the container is

111− # usable out of the box and tools that shell out don't fail.

112− pkgsLinux.coreutils-full

113− # Networking glue glibc needs: /etc/nsswitch.conf (+passwd,

114− # group) so DNS/host lookups resolve, and /etc/protocols,

115− # /etc/services. Without these, hostname resolution fails.

116− pkgsLinux.fakeNss

117− pkgsLinux.iana-etc

118− # The terminfo database (+ tput/clear/reset) so TUIs find the

119− # entry for whatever TERM `c` passes in and render correctly.

120− pkgsLinux.ncurses

121− # The session `c start` always launches.

122− pkgsLinux.herdr

123− ];

124− # Link all of /etc so the above files (nsswitch.conf, protocols,

125− # services, passwd, group, ssl certs) are present.

126− pathsToLink = [

127− "/bin"

128− "/etc"

129− ];

83+ packages:

84+ let

85+ pkgList = packages {

86+ pkgs = pkgsLinux;

87+ nur = nurPkgs;

13088 };

89+ in

90+ pkgsLinux.lib.warnIf (!builtins.any (p: (p.pname or "") == "fish") pkgList)

91+ "nix-container: config.cmd is /bin/fish but the package set has no `fish` — the container will fail to start unless something provides /bin/fish (or change config.cmd)."

92+ (

93+ n2c.buildImage {

94+ name = imageName;

95+ tag = imageTag;

96+ inherit arch;

13197

132− initializeNixDatabase = true;

98+ # A plain, single-process root filesystem. No NixOS, no systemd.

99+ copyToRoot = pkgsLinux.buildEnv {

100+ name = "root";

101+ paths = pkgList;

102+ pathsToLink = [ "/bin" ];

103+ };

133104

134− config = {

135− # `cmd` (not `entrypoint`): the default command, *replaced* by any

136− # command passed to `container run/create`. Plain herdr here;

137− # `c init` overrides it with `herdr session attach <dir>-container` so

138− # the session is named per project. `c start` attaches via

139− # `container start -ai`; exiting herdr (PID1) stops the container.

140− cmd = [ "/bin/herdr" ];

141− env = [

142− "PATH=/bin"

143− "HOME=/root"

144− # Default shell for tools that spawn one (herdr panes, etc.).

145− "SHELL=/bin/${shell}"

146− # Marker so shells/scripts can detect they're in here.

147− "NIX_CONTAINER=1"

148− # Advertise truecolor for 24-bit-aware tools; `c` passes the

149− # resolved TERM via -e (the runtime would otherwise force xterm).

150− "COLORTERM=truecolor"

151− # A UTF-8 locale so tools handle multibyte/wide characters

152− # correctly. glibc ships C.UTF-8 built in, so this needs no

153− # locale-archive.

154− "LANG=C.UTF-8"

155− # CA trust for every TLS client (curl/git/…) and Nix.

156− "SSL_CERT_FILE=/etc/ssl/certs/ca-bundle.crt"

157− "NIX_SSL_CERT_FILE=/etc/ssl/certs/ca-bundle.crt"

158− # Make the bundled Nix usable: flake commands on, and

159− # single-user (no daemon/nixbld).

160− "NIX_CONFIG=experimental-features = nix-command flakes\nbuild-users-group =\nsandbox = false"

161− ];

162− };

163− };

105+ initializeNixDatabase = true;

106+

107+ config = {

108+ # `cmd` (not `entrypoint`): it's the default command and is

109+ # *replaced* by `container run … -- <cmd>`. An entrypoint would

110+ # be prepended instead, so `run … -- /bin/sh` would become

111+ # `/bin/bash /bin/sh` and fail with "cannot execute binary file".

112+ cmd = [ "/bin/fish" ];

113+ env = [

114+ "PATH=/bin"

115+ "HOME=/root"

116+ # Marker so shells/scripts can detect they're in here.

117+ "NIX_CONTAINER=1"

118+ ];

119+ };

120+ }

121+ );

164122

165123 # `nix run . -- init|start` runs the bundled `c` manager script. Its

166124 # `init` builds the image from the project's `container.nix` (via

167− # `lib.copyWithShell`); the script finds the flake from its own (store)

125+ # `lib.copyWith`); the script finds the flake from its own (store)

168126 # location, so this works from a checkout or straight from

169127 # `nix run github:…/nix-container`.

170128 cApp = pkgsHost.writeShellScriptBin "c" ''

@@ -177,22 +135,15 @@

177135 default = flake-utils.lib.mkApp { drv = cApp; };

178136 };

179137

180− # Build helpers take a `{ pkgs, nur }: [ ... ]` packages function (the

181− # `packages` attr of a project's `container.nix`). `c init` uses

182− # `copyWithShell` (host shell baked in); `copyWith` is the generic form:

138+ # Build helpers. `c init` uses `copyWith` to honour a per-project

139+ # `container.nix`:

183140 # (builtins.getFlake "github:…/nix-container")

184− # .lib.<system>.copyWith (import ./container.nix).packages

141+ # .lib.<system>.copyWith (import ./container.nix)

185142 lib = {

186143 inherit mkImage;

187− # Build the image's `copyTo` script (a skopeo-copy wrapper) from a

188− # `{ pkgs, nur }: [ ... ]` function, named `imageName`. Defaults the

189− # shell (cmd + $SHELL) to bash; use `copyWithShell` to pick another.

190− copyWith = packages: (mkImage imageName "bash" packages).copyTo;

191− # Like `copyWith`, but for the given image `name` and shell — `c init`

192− # passes `nix-container-<dir>` and the host login shell, which is added

193− # to the image and used as cmd + $SHELL without being listed in

194− # `container.nix`.

195− copyWithShell = name: shell: packages: (mkImage name shell packages).copyTo;

144+ # skopeo copy app (`skopeo copy nix:<image> "$@"`) for an image built

145+ # from a `{ pkgs, nur }: [ ... ]` function.

146+ copyWith = packages: (mkImage packages).copyTo;

196147 };

197148 }

198149 );