Package as a dedicated tsunagi user; add Arch packages

Reworks the Linux packaging so the service runs as an unprivileged, dedicated
"tsunagi" user instead of root — the point of a native package is to set things
up properly for that OS's users — and adds Arch Linux packages beside the deb.
Both package families are built from the already-compiled static binary; nothing
is recompiled.

Service model (shared systemd unit, dist/linux/tsunagi.service):
- User=tsunagi with AmbientCapabilities=CAP_NET_ADMIN CAP_NET_BIND_SERVICE, so
  it creates the TUN and binds low ports without root.
- StateDirectory/CacheDirectory/RuntimeDirectory give it /var/lib/tsunagi,
  /var/cache/tsunagi and /run/tsunagi, and the agent is pointed at them (and the
  socket at /run/tsunagi/agent.sock) through TSUNAGI_* env in the unit.
- The polkit rule now grants the resolve1 actions to the "tsunagi" group; the
  service user is in it, and admins can add themselves.

CLI: when no state dir is chosen, the control commands prefer the system
service's socket at /run/tsunagi/agent.sock when it exists, so `sudo tsunagi
status`/`join` reach the packaged daemon with no flags. A per-user agent (its
socket absent from /run) still uses its own.

Packaging:
- deb (build-deb.sh): postinst now creates the tsunagi system user+group; unit
  installed to /lib/systemd/system, binary to /usr/bin.
- Arch (new dist/arch/build-pkg.sh): a dependency-free .pkg.tar.zst assembled
  with bsdtar + zstd (no makepkg, no Arch host) — .PKGINFO, a .INSTALL scriptlet
  that creates the user and reloads systemd, and a gzipped .MTREE; unit to
  /usr/lib/systemd/system.
- The polkit rule moved to dist/linux (shared by deb, Arch and the tarball), and
  the tarball install.sh now creates the user and installs the unit + rule.
- Both release workflows build the deb and the Arch package on the two Linux
  matrix entries (deb_arch/pkg_arch), install libarchive-tools+zstd for it, and
  attach both to the release (Gitea API loop / gh).

Not exercised in this session: the .deb and .pkg.tar.zst build and install only
on Linux (no dpkg-deb/bsdtar+pacman locally); CLI build, clippy, fmt and tests
pass, and all shell/YAML is syntax-checked.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitea/workflows/release.yml

@@ -35,6 +35,7 @@ jobs:
             zig: true
             deb: true
             deb_arch: amd64
+            pkg_arch: x86_64
           - os: ubuntu-latest
             target: aarch64-unknown-linux-musl
             asset: tsunagi-linux-aarch64
@@ -42,6 +43,7 @@ jobs:
             zig: true
             deb: true
             deb_arch: arm64
+            pkg_arch: aarch64
           - os: macos-latest
             target: aarch64-apple-darwin
             asset: tsunagi-macos-aarch64
@@ -67,9 +69,9 @@ jobs:
       # aws-lc-sys (iroh's rustls backend) and the bundled sqlite are C, and the
       # musl targets have no prebuilt bindings, so bindgen needs libclang and the
       # C build needs cmake. zig is the cross C compiler cargo-zigbuild drives.
-      - name: Install musl build tooling
+      - name: Install musl build and packaging tooling
         if: matrix.zig
-        run: sudo apt-get update && sudo apt-get install -y --no-install-recommends cmake clang libclang-dev
+        run: sudo apt-get update && sudo apt-get install -y --no-install-recommends cmake clang libclang-dev libarchive-tools zstd
       - name: Install zig
         if: matrix.zig
         uses: mlugg/setup-zig@v2
@@ -118,7 +120,8 @@ jobs:
           cp README.md "$stage/"
           case "${{ runner.os }}" in
             Linux)
-              cp dist/linux/tsunagi.service dist/linux/install.sh "$stage/"
+              cp dist/linux/tsunagi.service dist/linux/install.sh \
+                 dist/linux/50-tsunagi-resolved.rules "$stage/"
               cp dist/linux/README.md "$stage/INSTALL.md"
               ;;
             macOS)
@@ -152,6 +155,22 @@ jobs:
             "$version" \
             "tsunagi_${version}_${{ matrix.deb_arch }}.deb"
 
+      # A dependency-free Arch package (.pkg.tar.zst), assembled with bsdtar and
+      # zstd (no makepkg); same binary, service and polkit rule. See
+      # dist/arch/build-pkg.sh.
+      - name: Build the Arch package
+        if: matrix.pkg_arch
+        shell: bash
+        run: |
+          set -euo pipefail
+          version="${GITHUB_REF_NAME#v}"
+          pkgver="${version//-/_}"
+          bash dist/arch/build-pkg.sh \
+            "target/${{ matrix.target }}/release/tsunagi" \
+            "${{ matrix.pkg_arch }}" \
+            "$version" \
+            "tsunagi-${pkgver}-1-${{ matrix.pkg_arch }}.pkg.tar.zst"
+
       # @v3 on purpose: Gitea does not support the v4 artifact backend. This is
       # what makes the archive (and the .deb, where built) show up under the run
       # and hands it to `publish`.
@@ -162,6 +181,7 @@ jobs:
           path: |
             ${{ matrix.asset }}-*.*
             *.deb
+            *.pkg.tar.zst
           if-no-files-found: error
 
   publish:
@@ -233,5 +253,5 @@ jobs:
               cat up.json >&2 || true
               rc=1
             fi
-          done < <(find artifacts -type f \( -name '*.tar.gz' -o -name '*.zip' -o -name '*.deb' \) -print0)
+          done < <(find artifacts -type f \( -name '*.tar.gz' -o -name '*.zip' -o -name '*.deb' -o -name '*.pkg.tar.zst' \) -print0)
           exit "$rc"

.github/workflows/release.yml

@@ -36,6 +36,7 @@ jobs:
             zig: true
             deb: true
             deb_arch: amd64
+            pkg_arch: x86_64
           - os: ubuntu-latest
             target: aarch64-unknown-linux-musl
             asset: tsunagi-linux-aarch64
@@ -43,6 +44,7 @@ jobs:
             zig: true
             deb: true
             deb_arch: arm64
+            pkg_arch: aarch64
           - os: macos-latest
             target: aarch64-apple-darwin
             asset: tsunagi-macos-aarch64
@@ -68,9 +70,9 @@ jobs:
       # aws-lc-sys (iroh's rustls backend) and the bundled sqlite are C, and the
       # musl targets have no prebuilt bindings, so bindgen needs libclang and the
       # C build needs cmake. zig is the cross C compiler cargo-zigbuild drives.
-      - name: Install musl build tooling
+      - name: Install musl build and packaging tooling
         if: matrix.zig
-        run: sudo apt-get update && sudo apt-get install -y --no-install-recommends cmake clang libclang-dev
+        run: sudo apt-get update && sudo apt-get install -y --no-install-recommends cmake clang libclang-dev libarchive-tools zstd
       - name: Install zig
         if: matrix.zig
         uses: mlugg/setup-zig@v2
@@ -119,7 +121,8 @@ jobs:
           cp README.md "$stage/"
           case "${{ runner.os }}" in
             Linux)
-              cp dist/linux/tsunagi.service dist/linux/install.sh "$stage/"
+              cp dist/linux/tsunagi.service dist/linux/install.sh \
+                 dist/linux/50-tsunagi-resolved.rules "$stage/"
               cp dist/linux/README.md "$stage/INSTALL.md"
               ;;
             macOS)
@@ -153,6 +156,22 @@ jobs:
             "$version" \
             "tsunagi_${version}_${{ matrix.deb_arch }}.deb"
 
+      # A dependency-free Arch package (.pkg.tar.zst), assembled with bsdtar and
+      # zstd (no makepkg); same binary, service and polkit rule. See
+      # dist/arch/build-pkg.sh.
+      - name: Build the Arch package
+        if: matrix.pkg_arch
+        shell: bash
+        run: |
+          set -euo pipefail
+          version="${GITHUB_REF_NAME#v}"
+          pkgver="${version//-/_}"
+          bash dist/arch/build-pkg.sh \
+            "target/${{ matrix.target }}/release/tsunagi" \
+            "${{ matrix.pkg_arch }}" \
+            "$version" \
+            "tsunagi-${pkgver}-1-${{ matrix.pkg_arch }}.pkg.tar.zst"
+
       - name: Upload the build outputs as run artifacts
         uses: actions/upload-artifact@v4
         with:
@@ -160,6 +179,7 @@ jobs:
           path: |
             ${{ matrix.asset }}-*.*
             *.deb
+            *.pkg.tar.zst
           if-no-files-found: error
 
   publish:
@@ -188,7 +208,7 @@ jobs:
 
           # download-artifact@v4 nests each artifact under its own directory, so
           # the archives are artifacts/<asset>/<file>.
-          mapfile -t files < <(find artifacts -type f \( -name '*.tar.gz' -o -name '*.zip' -o -name '*.deb' \))
+          mapfile -t files < <(find artifacts -type f \( -name '*.tar.gz' -o -name '*.zip' -o -name '*.deb' -o -name '*.pkg.tar.zst' \))
           printf 'asset: %s\n' "${files[@]}"
 
           prerelease=()

crates/tsunagi-cli/src/main.rs

@@ -761,6 +761,17 @@ fn control_socket(
     if !_is_custom_state_dir {
         return tsunagi::ipc::default_control_socket_path();
     }
+    // When the user did not choose a state directory, prefer a running system
+    // service's socket, so `sudo tsunagi status` reaches the packaged daemon —
+    // which binds there via TSUNAGI_CONTROL_SOCKET — with no flags. Only when it
+    // is actually present, so a per-user agent still uses its own socket.
+    #[cfg(all(unix, not(target_os = "macos")))]
+    if !_is_custom_state_dir {
+        let system = std::path::Path::new("/run/tsunagi/agent.sock");
+        if system.exists() {
+            return system.to_path_buf();
+        }
+    }
     tsunagi::ipc::control_socket_path(&paths.state_dir)
 }
 

dist/arch/README.md

@@ -0,0 +1,52 @@
+# Running tsunagi on Arch Linux
+
+Install the package built for your architecture:
+
+```sh
+sudo pacman -U tsunagi-*-x86_64.pkg.tar.zst
+```
+
+It drops a static, dependency-free binary at `/usr/bin/tsunagi`, a systemd
+service, and a polkit rule, and creates a dedicated system user `tsunagi` the
+service runs as.
+
+Start it:
+
+```sh
+sudo systemctl enable --now tsunagi
+```
+
+Control it with `sudo` (the agent's control socket is private to the service
+user; `sudo` reaches it with no extra flags, because the CLI finds the running
+service's socket at `/run/tsunagi/agent.sock`):
+
+```sh
+sudo tsunagi status
+sudo tsunagi join <network-name> <tsn1…secret>
+```
+
+## How it runs
+
+The service runs as the unprivileged `tsunagi` user with just two capabilities
+(`CAP_NET_ADMIN`, `CAP_NET_BIND_SERVICE`) granted by systemd — no root. systemd
+creates and owns its directories:
+
+| what | path |
+|---|---|
+| state | `/var/lib/tsunagi` |
+| cache | `/var/cache/tsunagi` |
+| control socket | `/run/tsunagi/agent.sock` |
+
+The polkit rule lets anyone in the `tsunagi` group configure systemd-resolved
+for the overlay zones (the service user is in that group). To run the agent as
+your own user as well, add yourself to the group: `sudo usermod -aG tsunagi
+"$USER"`.
+
+## Removal
+
+```sh
+sudo pacman -R tsunagi
+```
+
+stops and disables the service. The `tsunagi` user and `/var/lib/tsunagi` are
+left in place; remove them by hand if you want them gone.

dist/arch/build-pkg.sh

@@ -0,0 +1,95 @@
+#!/usr/bin/env bash
+# Assemble an Arch Linux package (.pkg.tar.zst) from a prebuilt static tsunagi
+# binary, using only bsdtar + zstd on a non-Arch host — no makepkg, no Arch
+# container. The binary is static, so the package has no dependencies.
+#
+# Usage: build-pkg.sh <binary> <arch> <version> <output.pkg.tar.zst>
+#   <binary>  path to the built tsunagi executable
+#   <arch>    pacman architecture: x86_64 or aarch64
+#   <version> package version (the tag without its leading v)
+#   <output>  path to write the package to
+#
+# Needs bsdtar (libarchive-tools) and zstd on the builder.
+set -euo pipefail
+
+binary="$1"
+arch="$2"
+version="$3"
+output="$4"
+
+here="$(cd "$(dirname "$0")" && pwd)"
+root="$(mktemp -d)"
+trap 'rm -rf "$root"' EXIT
+
+# pacman pkgver may not contain '-', so a prerelease tag like 0.1.0-rc.9 becomes
+# 0.1.0_rc.9.
+pkgver="$(printf '%s' "$version" | tr '-' '_')"
+pkgrel=1
+
+# Payload. Arch keeps units under /usr/lib/systemd/system and installs to
+# /usr/bin, so the service's ExecStart is rewritten to match.
+install -D -m 0755 "$binary" "$root/usr/bin/tsunagi"
+
+mkdir -p "$root/usr/lib/systemd/system"
+sed 's#/usr/local/bin/tsunagi#/usr/bin/tsunagi#' \
+    "$here/../linux/tsunagi.service" > "$root/usr/lib/systemd/system/tsunagi.service"
+chmod 0644 "$root/usr/lib/systemd/system/tsunagi.service"
+
+install -D -m 0644 "$here/../linux/50-tsunagi-resolved.rules" \
+    "$root/usr/share/polkit-1/rules.d/50-tsunagi-resolved.rules"
+install -D -m 0644 "$here/../../README.md" "$root/usr/share/doc/tsunagi/README.md"
+install -D -m 0644 "$here/../linux/README.md" "$root/usr/share/doc/tsunagi/INSTALL.md"
+
+# Installed size (payload only), before the metadata files are written.
+size="$(du -sb "$root" | cut -f1)"
+
+cat > "$root/.PKGINFO" <<PKGINFO
+pkgname = tsunagi
+pkgver = ${pkgver}-${pkgrel}
+pkgdesc = Serverless private mesh networking agent
+url = https://github.com/Ultradesu/tsunagi
+builddate = $(date +%s)
+packager = AB <ab@hexor.cy>
+size = ${size}
+arch = ${arch}
+license = MIT
+license = Apache
+PKGINFO
+
+# Scriptlet: create the dedicated system user the service runs as, and keep
+# systemd in step. The "tsunagi" user is in the "tsunagi" group, which the
+# polkit rule grants the resolver actions.
+cat > "$root/.INSTALL" <<'INSTALL'
+post_install() {
+    getent group tsunagi >/dev/null 2>&1 || groupadd -r tsunagi
+    getent passwd tsunagi >/dev/null 2>&1 || \
+        useradd -r -g tsunagi -d /var/lib/tsunagi -s /usr/bin/nologin -c "tsunagi agent" tsunagi
+    systemctl daemon-reload >/dev/null 2>&1 || true
+}
+post_upgrade() {
+    post_install
+}
+pre_remove() {
+    systemctl disable --now tsunagi.service >/dev/null 2>&1 || true
+}
+post_remove() {
+    systemctl daemon-reload >/dev/null 2>&1 || true
+}
+INSTALL
+
+# .MTREE over the metadata and payload (not over itself), gzip-compressed, as
+# pacman expects.
+(
+    cd "$root"
+    LANG=C bsdtar -czf .MTREE --format=mtree \
+        --options='!all,use-set,type,uid,gid,mode,time,size,md5,sha256,link' \
+        .PKGINFO .INSTALL usr
+)
+
+# Pack with .PKGINFO first, then the rest, and zstd-compress.
+(
+    cd "$root"
+    bsdtar -cf - .PKGINFO .MTREE .INSTALL usr
+) | zstd -c -19 -T0 > "$output"
+
+echo "built $output"

dist/deb/50-tsunagi-resolved.rules

@@ -1,25 +0,0 @@
-// Installed by the tsunagi package.
-//
-// Lets a non-root agent configure systemd-resolved for its overlay zones — the
-// four resolve1 actions it calls, and nothing else — for any user in the
-// "tsunagi" group (created by the package). The packaged systemd service runs
-// as root and does not need this rule; it is for running the agent as your own
-// user instead:
-//
-//     sudo usermod -aG tsunagi "$USER"
-//     sudo setcap cap_net_admin,cap_net_bind_service+p /usr/bin/tsunagi
-//     tsunagi up
-//
-// polkit decides by user/group id, not by capability, which is why the resolver
-// needs this rule even once the binary has the capability.
-polkit.addRule(function(action, subject) {
-    var allowed = [
-        "org.freedesktop.resolve1.set-dns-servers",
-        "org.freedesktop.resolve1.set-domains",
-        "org.freedesktop.resolve1.set-default-route",
-        "org.freedesktop.resolve1.revert"
-    ];
-    if (allowed.indexOf(action.id) >= 0 && subject.isInGroup("tsunagi")) {
-        return polkit.Result.YES;
-    }
-});

dist/deb/build-deb.sh

@@ -29,7 +29,7 @@ sed 's#/usr/local/bin/tsunagi#/usr/bin/tsunagi#' \
     "$here/../linux/tsunagi.service" > "$root/lib/systemd/system/tsunagi.service"
 chmod 0644 "$root/lib/systemd/system/tsunagi.service"
 
-install -D -m 0644 "$here/50-tsunagi-resolved.rules" \
+install -D -m 0644 "$here/../linux/50-tsunagi-resolved.rules" \
     "$root/usr/share/polkit-1/rules.d/50-tsunagi-resolved.rules"
 install -D -m 0644 "$here/../../README.md" "$root/usr/share/doc/tsunagi/README.md"
 install -D -m 0644 "$here/../linux/README.md" "$root/usr/share/doc/tsunagi/INSTALL.md"
@@ -47,18 +47,24 @@ Homepage: https://github.com/Ultradesu/tsunagi
 Description: Serverless private mesh networking agent
  tsunagi forms small private mesh IP networks between peers, with NAT
  traversal and no central server. This package installs a static,
- dependency-free binary, a systemd service that runs the agent as root, and a
- polkit rule that lets a non-root agent configure systemd-resolved.
+ dependency-free binary, a systemd service that runs the agent as a dedicated
+ unprivileged "tsunagi" user with only CAP_NET_ADMIN and CAP_NET_BIND_SERVICE,
+ and a polkit rule for the local DNS resolver.
 CTRL
 
-# A system group for the optional non-root run (the polkit rule grants it the
-# resolve1 actions). The packaged service runs as root and does not need it.
+# The dedicated system user the service runs as. It is in the "tsunagi" group,
+# which the polkit rule grants the resolve1 actions. systemd creates the state,
+# cache and runtime directories for it on first start.
 cat > "$root/DEBIAN/postinst" <<'POSTINST'
 #!/bin/sh
 set -e
 if ! getent group tsunagi >/dev/null 2>&1; then
     addgroup --system tsunagi >/dev/null 2>&1 || true
 fi
+if ! getent passwd tsunagi >/dev/null 2>&1; then
+    adduser --system --ingroup tsunagi --home /var/lib/tsunagi --no-create-home \
+        --gecos "tsunagi agent" --disabled-login tsunagi >/dev/null 2>&1 || true
+fi
 if [ -d /run/systemd/system ]; then
     systemctl daemon-reload >/dev/null 2>&1 || true
 fi

dist/linux/50-tsunagi-resolved.rules

@@ -0,0 +1,23 @@
+// Installed by the tsunagi packages.
+//
+// polkit decides who may configure systemd-resolved by user/group id, not by
+// capability, so the agent needs this even though it holds CAP_NET_ADMIN. It
+// grants exactly the four resolve1 actions the agent calls, and nothing else,
+// to anyone in the "tsunagi" group.
+//
+// The packaged service runs as the "tsunagi" user (which is in that group), so
+// its resolver configuration is allowed. To also run the agent as your own
+// user, add yourself to the group:
+//
+//     sudo usermod -aG tsunagi "$USER"
+polkit.addRule(function(action, subject) {
+    var allowed = [
+        "org.freedesktop.resolve1.set-dns-servers",
+        "org.freedesktop.resolve1.set-domains",
+        "org.freedesktop.resolve1.set-default-route",
+        "org.freedesktop.resolve1.revert"
+    ];
+    if (allowed.indexOf(action.id) >= 0 && subject.isInGroup("tsunagi")) {
+        return polkit.Result.YES;
+    }
+});

dist/linux/README.md

@@ -2,40 +2,45 @@
 
 This archive holds a **static** `tsunagi` binary (musl), so it runs on any
 distribution — Arch, Alpine, NixOS, old glibc systems — with no shared-library
-dependencies. Alongside it are a systemd unit and an installer.
+dependencies. Alongside it are a systemd unit, a polkit rule, and an installer.
 
 Creating the TUN interface needs `CAP_NET_ADMIN`, and configuring
-systemd-resolved is decided by polkit (by user id, not capability). There are
-three ways to satisfy that; pick one.
+systemd-resolved is decided by polkit. There are three ways to run it; pick one.
 
-## Quick install — systemd service as root
+> On Debian/Ubuntu and Arch, prefer the native package (`.deb` / `.pkg.tar.zst`)
+> from the release — it does all of the below for you.
+
+## Quick install — systemd service as a dedicated user
 
 ```sh
 sudo ./install.sh
 sudo systemctl enable --now tsunagi
 ```
 
-The service runs the agent as root, so the interface, low ports and the
-resolver all just work (root is not subject to polkit). Control it **as root**,
-so the client resolves the same state directory the daemon uses:
+The service runs as an unprivileged `tsunagi` user with just `CAP_NET_ADMIN`
+and `CAP_NET_BIND_SERVICE` (granted by systemd), not root. systemd creates its
+state (`/var/lib/tsunagi`), cache (`/var/cache/tsunagi`) and runtime
+(`/run/tsunagi`) directories, and the polkit rule lets it configure the
+resolver. Control it with `sudo` — the CLI finds the running service's socket at
+`/run/tsunagi/agent.sock` with no flags:
 
 ```sh
 sudo tsunagi status
 sudo tsunagi join <network-name> <tsn1…secret>
 ```
 
-## As your own user — one capability, no root at runtime
+## As your own user — one capability, no service
 
 ```sh
 sudo install -m 0755 tsunagi /usr/local/bin/tsunagi
 sudo setcap cap_net_admin,cap_net_bind_service+p /usr/local/bin/tsunagi
+sudo usermod -aG tsunagi "$USER"   # so the resolver works; log in again after
 tsunagi up
 ```
 
-Nothing is left behind and nothing runs as root. The capability is lost on every
-rebuild or copy of the binary, so re-run `setcap` after replacing it. For the
-local DNS resolver, run `tsunagi dns` once: it prints the exact polkit rule that
-lets your user configure systemd-resolved, ready to paste.
+Nothing runs as root. The capability is lost on every rebuild or copy of the
+binary, so re-run `setcap` after replacing it. The agent uses your per-user
+state directory and socket, so plain `tsunagi status` (no sudo) reaches it.
 
 ## Without touching the OS
 

dist/linux/install.sh

@@ -1,10 +1,11 @@
 #!/usr/bin/env sh
-# Installs the tsunagi binary and, where systemd is present, a root service.
-# Run it as root (it writes under /usr/local and /etc):
+# Installs the static tsunagi binary and, where systemd is present, a service
+# that runs the agent as a dedicated unprivileged "tsunagi" user. Run as root:
 #
 #   sudo ./install.sh
 #
-# PREFIX overrides the install prefix (default /usr/local).
+# PREFIX overrides the install prefix (default /usr/local); if you change it,
+# edit ExecStart in tsunagi.service to match.
 set -eu
 
 PREFIX="${PREFIX:-/usr/local}"
@@ -19,8 +20,23 @@ echo "Installing tsunagi to ${PREFIX}/bin"
 install -d "${PREFIX}/bin"
 install -m 0755 "${here}/tsunagi" "${PREFIX}/bin/tsunagi"
 
+# The dedicated system user the service runs as (works with either shadow's
+# useradd or Debian's adduser).
+if ! getent group tsunagi >/dev/null 2>&1; then
+    groupadd -r tsunagi 2>/dev/null || addgroup --system tsunagi 2>/dev/null || true
+fi
+if ! getent passwd tsunagi >/dev/null 2>&1; then
+    useradd -r -g tsunagi -d /var/lib/tsunagi -s /usr/sbin/nologin -c "tsunagi agent" tsunagi 2>/dev/null \
+        || adduser --system --ingroup tsunagi --home /var/lib/tsunagi --no-create-home \
+            --gecos "tsunagi agent" --disabled-login tsunagi 2>/dev/null || true
+fi
+
+# polkit rule so the agent (as the tsunagi user) may configure systemd-resolved.
+install -d /etc/polkit-1/rules.d
+install -m 0644 "${here}/50-tsunagi-resolved.rules" /etc/polkit-1/rules.d/50-tsunagi-resolved.rules
+
 if command -v systemctl >/dev/null 2>&1; then
-    echo "Installing the systemd service (runs the agent as root)"
+    echo "Installing the systemd service (runs as the tsunagi user)"
     install -m 0644 "${here}/tsunagi.service" /etc/systemd/system/tsunagi.service
     systemctl daemon-reload
     cat <<EOF
@@ -29,7 +45,7 @@ Done. Start the agent with:
 
     sudo systemctl enable --now tsunagi
 
-Control it as root, so the client shares the agent's state directory:
+Control it with sudo (the CLI finds the service's socket automatically):
 
     sudo tsunagi status
     sudo tsunagi join <network-name> <tsn1…secret>
@@ -39,19 +55,11 @@ else
 
 Installed the binary; no systemd found, so no service was set up. Either:
 
-  * run it directly as root:
-
-        sudo tsunagi up
-
-  * or grant the capability and run it as your own user (no root at runtime):
-
-        sudo setcap cap_net_admin,cap_net_bind_service+p ${PREFIX}/bin/tsunagi
-        tsunagi up
-
-    For the local DNS resolver as a non-root user, run \`tsunagi dns\` once; it
-    prints the polkit rule that lets your user configure systemd-resolved.
-
-  * or skip the interface entirely with \`tsunagi up --no-tun\`: tunnels still
-    form, they just do not reach the operating system.
+  * run it as root:            sudo ${PREFIX}/bin/tsunagi up
+  * or as your own user:       sudo setcap cap_net_admin,cap_net_bind_service+p ${PREFIX}/bin/tsunagi
+                               tsunagi up
+    (add yourself to the tsunagi group so the resolver works:
+     sudo usermod -aG tsunagi "\$USER")
+  * or without touching the OS: tsunagi up --no-tun
 EOF
 fi

dist/linux/tsunagi.service

@@ -6,21 +6,31 @@ Wants=network-online.target
 
 [Service]
 Type=simple
+# Runs as a dedicated unprivileged user, not root. The two capabilities are all
+# it needs: CAP_NET_ADMIN to create and configure the TUN interface, and
+# CAP_NET_BIND_SERVICE for low ports. The packages create the `tsunagi` user.
+User=tsunagi
+Group=tsunagi
+AmbientCapabilities=CAP_NET_ADMIN CAP_NET_BIND_SERVICE
+CapabilityBoundingSet=CAP_NET_ADMIN CAP_NET_BIND_SERVICE
+
+# systemd creates and owns these for the service user, and the agent is pointed
+# at them: state in /var/lib/tsunagi, cache in /var/cache/tsunagi, and the
+# control socket in /run/tsunagi, which stays private to the service user.
+StateDirectory=tsunagi
+StateDirectoryMode=0700
+CacheDirectory=tsunagi
+RuntimeDirectory=tsunagi
+RuntimeDirectoryMode=0755
+Environment=TSUNAGI_STATE_DIR=%S/tsunagi
+Environment=TSUNAGI_CACHE_DIR=%C/tsunagi
+Environment=TSUNAGI_CONTROL_SOCKET=%t/tsunagi/agent.sock
+
+# The tarball installer puts the binary here; the deb and the Arch package
+# rewrite this to /usr/bin where they install it.
 ExecStart=/usr/local/bin/tsunagi up
 Restart=on-failure
 RestartSec=5
 
-# This unit runs the agent as root, which covers everything it needs: creating
-# the TUN interface (CAP_NET_ADMIN), binding low ports, and configuring
-# systemd-resolved — root is not subject to polkit, so no polkit rule is needed.
-#
-# To run as a non-root user instead, uncomment the three lines below, set a
-# User=, and install the polkit rule that `tsunagi dns` prints (resolved decides
-# by user id, not capability, so the rule is what lets a non-root agent set the
-# resolver):
-#User=tsunagi
-#AmbientCapabilities=CAP_NET_ADMIN CAP_NET_BIND_SERVICE
-#CapabilityBoundingSet=CAP_NET_ADMIN CAP_NET_BIND_SERVICE
-
 [Install]
 WantedBy=multi-user.target