diff --git a/CHANGELOG.md b/CHANGELOG.md
index 680c81c..ed2eded 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,8 +5,30 @@ which records not just what changed but what each drill run proved.
 
 ## Unreleased
 
+### Added
+
+- **Global / root install** (#71) — run as root, box installs *once* to
+  `/opt/box` (world-readable) with the `box` symlink on `/usr/local/bin`, so
+  every operator on a shared host runs the same tree. Per-user installs are
+  unchanged (`$HOME/.local`); `BOX_HOME`/`BOX_BIN` still override. A per-user
+  tree under `/root` is `0700` and unreadable to everyone else — the whole fleet
+  got `command not found` — so the root branch lands in a system location and
+  `chmod -R a+rX`'s it (read for files, +search on dirs), guarded on root. This
+  unblocks "rig installs box" (rig#24's `box` role).
+- **CI + a test suite** — `.github/workflows/ci.yml` (a `check` job: globstar
+  `shellcheck -x` over `bin/* **/*.sh`, then `bash test/cli.sh`) and `test/cli.sh`,
+  dependency-free and runnable by a non-root user with no Incus. It exercises the
+  `install.sh` DEST/BINDIR branch functionally (both tiers + `BOX_HOME`/`BOX_BIN`
+  overrides), the CLI contract, and grep-guards the daemon-gated invariants and
+  tmux in every template — the box was the repo with "no tests and no CI".
+
 ### Fixed
 
+- **`box tmux` works on every template** (#65) — `box tmux` runs
+  `tmux new-session` *inside* the box, but the templates did not install tmux, so
+  it failed with `tmux: command not found`. `tmux` is now in each template's
+  cloud-init package list (`blank`/`claude`/`codex`/`grok`).
+
 - **`box setup-host` finishes in one run** (#63). When it had to add you to
   `incus-admin` it stopped there and told you to re-login and re-run — an
   `exit 0` that reported success having built none of the stack: no `boxnet`,
diff --git a/README.md b/README.md
index de9e3d1..8317fe0 100644
--- a/README.md
+++ b/README.md
@@ -64,6 +64,25 @@ A version-aware upgrade that migrates boxes instead of asking you to is
 (CI, images), `BOX_YES=1` answers every prompt yes and `BOX_SKIP_SETUP_HOST=1`
 declines the host-setup step.
 
+### Global vs per-user install
+
+Where box lands depends on **who runs the installer**, because on a shared host
+box's tree is *executed by other users* — so it cannot hide in one user's home:
+
+- **As root → global.** The tree goes to `/opt/box` (world-readable) and the
+  `box` symlink to `/usr/local/bin` (already on every login `PATH`). One
+  install, every operator on the host runs the same `box`. This is the fleet
+  path: [rig](https://github.com/heavy-duty/rig)'s `box` role
+  ([rig#24](https://github.com/heavy-duty/rig/issues/24)) installs box once at
+  host bootstrap ([#71](https://github.com/heavy-duty/box/issues/71)).
+- **As a normal user → per-user.** The tree goes to `~/.local/share/box` and
+  the symlink to `~/.local/bin` — the solo path, unchanged. Nobody else needs
+  to run your box.
+
+`BOX_HOME` / `BOX_BIN` override the destination on either path. A per-user
+install under `/root` would be `0700` and unreadable to everyone else — which
+is exactly the bug the root branch fixes.
+
 ## One-time host setup (Ubuntu 24.04 / Debian 13)
 
 The installer already does this. Run it directly to set up a host you
diff --git a/install.sh b/install.sh
index 4eed235..a894f7d 100755
--- a/install.sh
+++ b/install.sh
@@ -10,8 +10,20 @@ set -euo pipefail
 
 REPO="${BOX_REPO:-heavy-duty/box}"
 REF="${BOX_REF:-main}"
-DEST="${BOX_HOME:-$HOME/.local/share/box}"
-BINDIR="${BOX_BIN:-$HOME/.local/bin}"
+# Root installs GLOBALLY, non-root installs per-user. box's install tree is
+# EXECUTED by other users (the multi-user host path: rig installs box once, every
+# incus-group operator runs it) — unlike rig, which is root-only and can hide in
+# /root. So a root install must land in a system location, not $HOME: /root is
+# 0700, so a $HOME/.local tree there is unreadable to everyone else and the whole
+# fleet gets 'command not found' (#71). /opt/box is the world-readable system
+# tree; /usr/local/bin is already on every login PATH. BOX_HOME/BOX_BIN still win.
+if [ "$(id -u)" -eq 0 ]; then
+  DEST="${BOX_HOME:-/opt/box}"
+  BINDIR="${BOX_BIN:-/usr/local/bin}"
+else
+  DEST="${BOX_HOME:-$HOME/.local/share/box}"
+  BINDIR="${BOX_BIN:-$HOME/.local/bin}"
+fi
 
 log() { printf 'box-install: %s\n' "$*"; }
 warn() { printf 'box-install: WARNING: %s\n' "$*" >&2; }
@@ -96,6 +108,16 @@ mv "$EXTRACTED" "$DEST"
 
 chmod +x "$DEST/bin/box"
 
+# A global (root) install is run by OTHER users, but mv preserves the tarball's
+# root:root ownership and GitHub's archives carry no world bits on some paths — so
+# without this, a non-root caller cannot even traverse into $DEST to reach bin/box.
+# Root owns the tree, nobody else writes it, everybody reads it. a+rX: read on
+# files, +search (x) on directories only. Guarded on root so the per-user install
+# stays byte-identical to before.
+if [ "$(id -u)" -eq 0 ]; then
+  chmod -R a+rX "$DEST"
+fi
+
 # --- put box on PATH -------------------------------------------------------
 mkdir -p "$BINDIR"
 ln -sf "$DEST/bin/box" "$BINDIR/box"
diff --git a/templates/blank/user-data.yaml b/templates/blank/user-data.yaml
index efe8ddf..e482c90 100644
--- a/templates/blank/user-data.yaml
+++ b/templates/blank/user-data.yaml
@@ -7,3 +7,9 @@ users:
     sudo: "ALL=(ALL) NOPASSWD:ALL"
     lock_passwd: true
 package_update: false
+# The one package a blank box still needs: 'box tmux' runs 'tmux new-session'
+# INSIDE the box, and a bare Debian image ships no tmux — without this it fails
+# with "tmux: command not found" (#65). cloud-init refreshes the apt lists on its
+# own whenever 'packages' is non-empty, so package_update stays false here.
+packages:
+  - tmux