diff --git a/eris/eris/tools.toml b/eris/eris/tools.toml
index 4cf7c04..480b92a 100644
--- a/eris/eris/tools.toml
+++ b/eris/eris/tools.toml
@@ -148,7 +148,7 @@ tools_for_extensions = [
 [unrar]
   dependencies = ["unrar"]
   url = "http://www.rarlabs.com/"
-  command = "unrar l"
+  command = "unrar-nonfree l"
 
 [7z]
   dependencies = ["p7zip"]
@@ -214,7 +214,7 @@ tools_for_extensions = [
   has_color = true
 
 [php8_syntax]
-  dependencies = ["php8.0-cli"]
+  dependencies = ["php-cli"]
   url = "https://en.wikipedia.org/wiki/PHP"
   command = "php --syntax-check"
 
@@ -237,7 +237,7 @@ tools_for_extensions = [
 [lua_syntax]
   dependencies = ["lua5.3"]
   url = "http://www.lua.org"
-  command = "luac -p"
+  command = "luac5.3 -p"
 
 [js_syntax]
   dependencies = ["nodejs"]
diff --git a/eris/eris/worker.py b/eris/eris/worker.py
index 69fbd54..dfb3923 100755
--- a/eris/eris/worker.py
+++ b/eris/eris/worker.py
@@ -31,7 +31,8 @@ class Worker:
         self.process = await create
         pid_line = await self.process.stdout.readline()
         self.child_pgid = int(pid_line.strip())
-        os.setpriority(os.PRIO_PGRP, self.child_pgid, 19)
+        if "SNAP" not in os.environ:  # Can't do setpriority inside snaps.
+            os.setpriority(os.PRIO_PGRP, self.child_pgid, 19)
         self.process.stdin.write(f"{self.compression}\n".encode("utf-8"))
 
     async def run_tool(self, path, tool):
diff --git a/packaging/make-snap b/packaging/make-snap
new file mode 100755
index 0000000..e43ce56
--- /dev/null
+++ b/packaging/make-snap
@@ -0,0 +1,19 @@
+#!/bin/bash
+
+
+# Run this script from the project root.
+# i.e. ./packaging/make-snap
+
+
+set -e
+set -x
+
+
+# snap install lxd
+# lxd init  # Use defaults. Set size of loop device to at least 3GB.
+
+snapcraft clean --use-lxd
+snapcraft --use-lxd --debug
+sudo snap remove eris
+sudo snap install --dangerous eris_*_amd64.snap
+/snap/bin/eris -h
diff --git a/packaging/make-snapcraft.py b/packaging/make-snapcraft.py
new file mode 100755
index 0000000..4edf8a1
--- /dev/null
+++ b/packaging/make-snapcraft.py
@@ -0,0 +1,70 @@
+#!/usr/bin/env python3.9
+# -*- coding: utf-8 -*-
+
+
+import textwrap
+
+import eris.__main__
+import eris.tools as tools
+
+
+def main():
+    lines = eris.__main__.__doc__.splitlines()
+    summary = lines[2]
+    description = textwrap.indent("\n".join(lines[2:]), "  ")
+    print(f"""\
+name: eris
+base: core20
+version: 2021.11.29
+summary: {summary}
+description: |
+{description}
+
+grade: devel
+confinement: strict
+
+apps:
+  eris:
+    command: bin/eris
+    environment:
+      PYTHONPATH: $SNAP/lib/python3.9/site-packages:$SNAP/lib/python3.9/dist-packages:$PYTHONPATH
+    plugs:
+      - home
+  webserver:
+    command: bin/eris-webserver
+    environment:
+      PYTHONPATH: $SNAP/lib/python3.9/site-packages:$SNAP/lib/python3.9/dist-packages:$PYTHONPATH
+    plugs:
+      - home
+      - network-bind
+
+passthrough:
+  layout:
+    $SNAP/usr/bin/php:
+      symlink: $SNAP/usr/bin/php7.4
+
+parts:
+  eris:
+    plugin: python
+    source: .
+    python-packages:
+      - ./termstr
+      - ./lscolors
+      - ./fill3
+      - ./eris
+    requirements:
+      - ./termstr/requirements.txt
+      - ./fill3/requirements.txt
+      - ./eris/requirements.txt
+    build-environment:
+      - SNAPCRAFT_PYTHON_INTERPRETER: python3.9
+    stage-packages:
+      - python3.9-venv
+      - python3-distutils
+      - python3-pkg-resources
+      - """, end="")
+    print("\n      - ".join(sorted(tools.dependencies())))
+
+
+if __name__ == "__main__":
+    main()
diff --git a/snap/snapcraft.yaml b/snap/snapcraft.yaml
new file mode 100644
index 0000000..fc193dc
--- /dev/null
+++ b/snap/snapcraft.yaml
@@ -0,0 +1,101 @@
+name: eris
+base: core20
+version: 2021.11.29
+summary: Eris maintains an up-to-date set of reports for every file in a codebase.
+description: |
+  Eris maintains an up-to-date set of reports for every file in a codebase.
+
+  A status indicator summarises the state of each report, and a report is viewed
+  by selecting this status indicator with the cursor.
+
+  The reports are cached in the codebase's root directory in a ".eris"
+  directory.
+
+grade: devel
+confinement: strict
+
+apps:
+  eris:
+    command: bin/eris
+    environment:
+      PYTHONPATH: $SNAP/lib/python3.9/site-packages:$SNAP/lib/python3.9/dist-packages:$PYTHONPATH
+    plugs:
+      - home
+  webserver:
+    command: bin/eris-webserver
+    environment:
+      PYTHONPATH: $SNAP/lib/python3.9/site-packages:$SNAP/lib/python3.9/dist-packages:$PYTHONPATH
+    plugs:
+      - home
+      - network-bind
+
+passthrough:
+  layout:
+    $SNAP/usr/bin/php:
+      symlink: $SNAP/usr/bin/php7.4
+
+parts:
+  eris:
+    plugin: python
+    source: .
+    python-packages:
+      - ./termstr
+      - ./lscolors
+      - ./fill3
+      - ./eris
+    requirements:
+      - ./termstr/requirements.txt
+      - ./fill3/requirements.txt
+      - ./eris/requirements.txt
+    build-environment:
+      - SNAPCRAFT_PYTHON_INTERPRETER: python3.9
+    stage-packages:
+      - python3.9-venv
+      - python3-distutils
+      - python3-pkg-resources
+      - binutils
+      - coreutils
+      - cppcheck
+      - dpkg
+      - elinks
+      - file
+      - g++
+      - gcc
+      - genisoimage
+      - git
+      - golang-go
+      - html2text
+      - lua-check
+      - lua5.3
+      - mediainfo
+      - nodejs
+      - p7zip
+      - pandoc
+      - perl
+      - perl-doc
+      - php-cli
+      - pylint
+      - python3-bandit
+      - python3-cairosvg
+      - python3-coverage
+      - python3-mccabe
+      - python3-mypy
+      - python3-pdfminer
+      - python3-pillow
+      - python3-pycodestyle
+      - python3-pydocstyle
+      - python3-pyflakes
+      - python3-pygments
+      - python3-pytest
+      - python3-pytest-cov
+      - rakudo
+      - rpm
+      - ruby2.7
+      - shellcheck
+      - tar
+      - tidy
+      - unrar
+      - unzip
+      - wabt
+      - xz-utils
+      - yamllint