Snap

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### Initial hello-world example: snapcraft.yaml and hello.sh

Source: https://snapcraft.io/docs/reference/interfaces/ros-opt-data-interface

The initial hello-world example snap, before adding ros-opt-data. The snapcraft.yaml defines a simple dump-based snap, and hello.sh just prints "hello world". These two files are shown as the starting point for the tutorial.

```yaml
name: hello-world
version: '0.1'
summary: A simple hello world application
description: |
  A simple hello world application.
base: core22

grade: devel
confinement: strict

apps:
  hello-world:
    command: ./hello.sh

parts:
  hello-world:
    plugin: dump
    source: files

```

```bash
#!/bin/bash
echo "hello world"

```

--------------------------------

### Download a snap and its assertions with snap download

Source: https://snapcraft.io/docs/explanation/security/assertions

Example of using the `snap download` command to fetch a snap and its assertions. The output shows the download progress and instructions to install the snap using `snap ack` and `snap install`.

```bash
$ snap download gnome-calculator
Fetching snap "gnome-calculator"
Fetching assertions for "gnome-calculator"
Install the snap with:
   snap ack gnome-calculator_945.assert
   snap install gnome-calculator_945.snap

```

--------------------------------

### Install the core snap

Source: https://snapcraft.io/docs/tutorials/install-the-daemon/raspberrypios

Install the core snap to get the latest snapd. The expected output is shown.

```bash
$ sudo snap install core
core 16-2.45.2 from Canonical✓ installed

```

--------------------------------

### Autostart desktop file example with snap.yaml and startup command

Source: https://snapcraft.io/docs/reference/development/yaml-schemas/the-snap-format

The snap.yaml sets the 'autostart' property to 'my-chat.desktop'. The desktop file in $SNAP_USER_DATA/.config/autostart provides the Exec line. The application is started as 'my-chat.chat --autostart a b c'.

```yaml
name: my-chat
version: 1.0
apps:
    chat:
        command: bin/my-chat
        autostart: my-chat.desktop

```

```ini
[Desktop Entry]
Name=My Chat
Exec=/usr/bin/my-chat --autostart a b c

```

```text
my-chat.chat --autostart a b c 

```

--------------------------------

### snapctl system-mode command and example output

Source: https://snapcraft.io/docs/how-to-guides/snap-development/use-snapctl

Returns YAML-formatted details about specific system states, including the current system mode, whether seeded snaps have finished installing, and whether the factory image hint is set. The output shown is an example of a UC20+ system in install mode with the factory hint enabled.

```bash
$ snapctl system-mode
system-mode: install
seed-loaded: true
factory: true

```

--------------------------------

### snap list output showing install modes

Source: https://snapcraft.io/docs/explanation/snap-development/install-modes

Example output of the snap list command showing the install mode in the Notes column. The Notes column displays devmode for snaps installed in developer mode and classic for classic snaps.

```text
Name        Version            Rev    Tracking        Publisher     Notes
liquidctl   1.7.1-11-g6295354  1      latest/stable   morrisong     devmode
snapcraft   5.0                6751   latest/stable   canonical✓    classic

```

--------------------------------

### snap debug timings --last=install output (cache and fresh install)

Source: https://snapcraft.io/docs/explanation/how-snaps-work/snap-performance

Example output from `snap debug timings --last=install` after installing the Chromium snap, first from cache and then fresh install. The `Doing` column shows task execution times.

```text
ID      Status        Doing      Undoing  Label                          Summary
160241  Done          461ms            -  prerequisites                  Ensure prerequisites for "chromium" are available
 ^                    353ms            -  install-prereq                 install "cups"
 ^                     12ms            -  install-prereq                 install base "core22"
160242  Done           62ms            -  download-snap                  Download snap "chromium" (2556) from channel "stable"
160243  Done          607ms            -  validate-snap                  Fetch and check assertions for snap "chromium" (2556)
160244  Done         2253ms            -  mount-snap                     Mount snap "chromium" (2556)
 ^                     75ms            -  check-snap                     check snap "chromium"
 ^                   2059ms            -  setup-snap                     setup snap "chromium"
160245  Done           61ms            -  copy-snap-data                 Copy snap "chromium" data
160246  Done          241ms            -  setup-profiles                 Setup snap "chromium" (2556) security profiles
 ^                     32ms            -  setup-security-backend         setup security backend "seccomp" for snap "chromium"
 ^                    133ms            -  setup-security-backend[many]   setup security backend "apparmor" for 1 snaps
  ^                   101ms            -  load-profiles[changed-many]    load changed security profiles of 1 snaps
160247  Done          396ms            -  link-snap                      Make snap "chromium" (2556) available to the system
 ^                      8ms            -  generate-wrappers              generate wrappers for snap chromium
 ^                    290ms            -  update-fc-cache                update font config caches
160248  Done          388ms            -  auto-connect                   Automatically connect eligible plugs and slots of snap "chromium"
160267  Done           92ms            -  connect                        Connect chromium:u2f-devices to snapd:u2f-devices
```

--------------------------------

### Install snap from explicit channel

Source: https://snapcraft.io/docs/explanation/how-snaps-work/channels-and-tracks

Installs a snap from an explicitly specified channel. Here, 'latest/edge' is used as an example, but any valid channel can be specified.

```bash
snap install vlc --channel=latest/edge

```

--------------------------------

### Install snap components with snap install

Source: https://snapcraft.io/docs/how-to-guides/manage-snaps/using-components

Installs the snap my-snap along with components comp1 and comp2. If the snap is already installed, only the missing components are installed. The syntax <snap_name>+<comp_1>+...+<comp_N> is used to refer to components from the command line.

```bash
snap install my-snap+comp1+comp2

```

--------------------------------

### Install snaps as a single transaction with --transaction=all-snaps

Source: https://snapcraft.io/docs/explanation/how-snaps-work/transactional-updates

Installs the hello and hello-world snaps as a single transaction using the --transaction=all-snaps argument. The output shows both snaps installed successfully, but no change, log, or message indicates that the set was installed as a single transaction.

```bash
$ snap install hello hello-world --transaction=all-snaps
hello-world 6.4 from Canonical✓ installed
hello 2.10 from Canonical✓ installed

```

--------------------------------

### Install an unpacked snap with snap try

Source: https://snapcraft.io/docs/how-to-guides/snap-development/snap-try

Installs an unpacked snap using a bind mount. The output shows the snap being mounted and the location of the installed command.

```bash
$ snap try squashfs-root
hello-world 6.4 mounted from /home/user/squashfs-root
$ which hello-world
/snap/bin/hello-world

```

--------------------------------

### snap install hello-world --revision 27

Source: https://snapcraft.io/docs/explanation/how-snaps-work/revisions

Installs revision 27 of the hello-world snap. The output confirms the installed revision.

```bash
$ snap install hello-world --revision 27
hello-world 6.3 from Canonical✓ installed

```

--------------------------------

### Install Snapcraft

Source: https://snapcraft.io/docs/snapcraft-overview

Installs Snapcraft as a snap with classic confinement.

```bash
snap install snapcraft --classic
```

--------------------------------

### Install snap from beta channel

Source: https://snapcraft.io/docs/explanation/how-snaps-work/channels-and-tracks

Installs VLC from the beta risk-level. If the beta snap is not available, the snap is installed from the closest channel with a more stable risk-level.

```bash
sudo snap install --channel=beta vlc

```

--------------------------------

### Install snapd on openSUSE

Source: https://snapcraft.io/docs/tutorials/install-the-daemon/opensuse

Installs the snapd package using zypper.

```bash
sudo zypper install snapd

```

--------------------------------

### Start and enable a service

Source: https://snapcraft.io/docs/how-to-guides/manage-snaps/control-services

Starts a service and re-enables its automatic start on system boot.

```bash
snap start --enable lxd.daemon

```

--------------------------------

### Install snapd with pacman

Source: https://snapcraft.io/docs/tutorials/install-the-daemon/manjaro-linux

Installs the snapd package from the command line. Run this if snap is not already installed or has been removed.

```bash
sudo pacman -S snapd

```

--------------------------------

### Install components from local files with --dangerous flag

Source: https://snapcraft.io/docs/how-to-guides/manage-snaps/using-components

Installs components from a local file. Unasserted components can only be installed if the host snap is unasserted too, and the --dangerous flag is required.

```bash
snap install --dangerous ./my-snap+comp1+comp2_1.0.comp

```

--------------------------------

### Install LXD

Source: https://snapcraft.io/docs/snapcraft-overview

Installs LXD, the build provider that containerizes the build environment.

```bash
snap install lxd
```

--------------------------------

### Install snap with --dangerous

Source: https://snapcraft.io/docs/snapcraft-overview

Installs the locally built snap with --dangerous because it is not from the Snap Store and thus not checked for safety.

```bash
snap install ukuzama-pyfiglet_0.1_amd64.snap --dangerous

```

--------------------------------

### Start an interactive shell during packaging with `snapcdd` --shell interactive shell. description: Run `sn_large.png

Source: https://snapcraft.io/docs/snapcraft-overview

Run `snapcraft pack --shell interactive shell inside the interactive shell. description: 

```bash_code
sn? Actually, exact code exactly as in source preserving whitespace preserving line breaks.actual code block content exactly as in source verbatim preserving whitespace and line breaks exactly as they appear.page_titleInspect the result: inspecting the build container and file structure. page_description: 
```

--------------------------------

### Run snap with font and show output

Source: https://snapcraft.io/docs/snapcraft-overview

Runs the snap with the installed font, omitting the .tlf extension, and shows the expected braille output.

```bash
ukuzama-pyfiglet -f smbraille hello, world!
⣇⡀ ⢀⡀ ⡇ ⡇ ⢀⡀    ⡀ ⢀ ⢀⡀ ⡀⣀ ⡇ ⢀⣸ ⡇
⠇⠸ ⠣⠭ ⠣ ⠣ ⠣⠜,   ⠱⠱⠃ ⠣⠜ ⠏  ⠣ ⠣⠼ ⠅

```

--------------------------------

### Install font with -L

Source: https://snapcraft.io/docs/snapcraft-overview

Installs a font (Small Braille) from the figlet-fonts project.

```bash
ukuzama-pyfiglet -L smbraille.tlf

```

--------------------------------

### GET request to /v2/apps with jq formatting

Source: https://snapcraft.io/docs/how-to-guides/snap-development/use-the-rest-api

This example sends a GET request to the /v2/apps endpoint and pipes the response through jq for formatting. The output shows a JSON object with type sync, status-code 200, and a result array containing snap details. Use this to retrieve and inspect the list of installed snaps.

```bash
$ sudo curl -sS --unix-socket /run/snapd.socket http://localhost/v2/apps \
| jq
{
  "type": "sync",
  "status-code": 200,
  "status": "OK",
  "result": [
    {
      "snap": "anbox-installer",
      "name": "anbox-installer"
    }
  ]
}

```

--------------------------------

### Test snap installation with hello-world

Source: https://snapcraft.io/docs/tutorials/install-the-daemon/arch-linux

Installs the hello-world snap and runs it to verify the system is set up correctly.

```bash
$ sudo snap install hello-world
hello-world 6.3 from Canonical✓ installed
$ hello-world
Hello World!

```

--------------------------------

### Install snap-http Python package

Source: https://snapcraft.io/docs/how-to-guides/snap-development/use-the-rest-api

Install the snap-http Python package, which provides a Python interface to the snapd REST API. After installation, refer to the snap-http repository for documentation and usage examples.

```bash
pip install snap-http

```

--------------------------------

### Install multiple snap instances with instance key

Source: https://snapcraft.io/docs/explanation/how-snaps-work/parallel-installs

Install two instances of the hello-world snap in one command. The second instance uses the instance key 'foo' appended with an underscore. Each instance is isolated from the others.

```bash
sudo snap install hello-world hello-world_foo

```

--------------------------------

### Build and serve live preview with make run

Source: https://snapcraft.io/docs/contributing/local-development

Builds and serves the documentation at http://127.0.0.1:8000/ with live reload on file changes. Use this command to start a local preview while editing.

```make
make run

```

--------------------------------

### snapcraft edit-validation-sets example

Source: https://snapcraft.io/docs/how-to-guides/manage-snaps/manage-validation-sets

Example command using a sample account ID, set name 'myset1', and sequence 1. The sequence number starts at 1.

```bash
snapcraft edit-validation-sets xSfWKGdLoQBoQx88vIM1MpbFNMq53t1f myset1 1

```

--------------------------------

### Install snap file with --name instance key

Source: https://snapcraft.io/docs/explanation/how-snaps-work/parallel-installs

Install a snap from a local .snap file with an explicit instance key. The --name flag sets the instance name (snap_instance) when installing from a file.

```bash
sudo snap install --name hello-world_foo hello-world_27.snap

```

--------------------------------

### Initialize snap project with snapcraft init

Source: https://snapcraft.io/docs/snapcraft-overview

Runs the `snapcraft init` command to generate a template `snapcraft.yaml` file in the `snap/` directory.

```bash
snapcraft init

```

--------------------------------

### Install the snapd snap for latest features

Source: https://snapcraft.io/docs/tutorials/install-the-daemon/debian

After installing snapd and restarting the system, install the snapd snap to get the latest snapd. Some snaps may require new snapd features and show an error like 'snap "lxd" assumes unsupported features' if not updated.

```bash
sudo snap install snapd

```

--------------------------------

### Configure polkit interface with action-prefix and install-rules

Source: https://snapcraft.io/docs/reference/interfaces/polkit-interface

Snapcraft YAML configuration for the polkit interface. Sets the action-prefix to org.example.foo and installs a polkit rule file named polkit.bar.rules with its sha3-384 hash. The app named 'app' runs command 'foo' and plugs into the polkit interface.

```yaml
plugs:
 polkit:
  action-prefix: org.example.foo
  install-rules:
      - name: polkit.bar.rules
        sha3-384: 2YM8oyXyE7xuXR07EXqUpixvr8duiJwgPQqhnxZgrBCU8ZSDowV0Gyujvs1j0-KR

apps:
 app:
  command: foo
  plugs: [polkit]

```

--------------------------------

### Enable snapd.apparmor.service for confinement

Source: https://snapcraft.io/docs/tutorials/install-the-daemon/arch-linux

Enables and starts the AppArmor service for snap confinement. Requires AppArmor to be installed and enabled first.

```bash
sudo systemctl enable --now snapd.apparmor.service

```

--------------------------------

### snap debug timings --startup=ifacemgr

Source: https://snapcraft.io/docs/explanation/how-snaps-work/snap-performance

Use the `--startup` argument with `snap debug timings` to output startup timing data for the `ifacemgr` subsystem. The output shows execution times for setting up security profiles for installed snaps before snapd becomes operational.

```bash
$ snap debug timings --startup=ifacemgr
ID        Status        Doing      Undoing  Summary
ifacemgr                    -            -  
 ^                        8ms            -    setup security backend "apparmor" for snap "core"
 ^                        7ms            -    setup security backend "mount" for snap "lxd"
 ^                       16ms            -    setup security backend "apparmor" for snap "lxd"
 ^                       12ms            -    load unchanged security profiles of snap "lxd"
 ^                        7ms            -    setup security backend "apparmor" for snap "vlc"
 ^                        5ms            -    load unchanged security profiles of snap "vlc"


```

--------------------------------

### snap list output with Rev column

Source: https://snapcraft.io/docs/explanation/how-snaps-work/revisions

Example output of `snap list` showing the `Rev` column with each installed snap's revision number.

```text
Name         Version  Rev    Tracking       Publisher             Notes
alacritty    0.8.0    46     latest/stable  snapcrafters✪         classic
blender      3.5.0    3486   latest/stable  blenderfoundation✓    classic
chromium     112.0    2424   latest/stable  canonical✓            -
ffmpeg       4.3.1    1286   latest/stable  snapcrafters✪         -

```

--------------------------------

### snap get nextcloud

Source: https://snapcraft.io/docs/how-to-guides/manage-snaps/configure-snaps

Displays the configuration options of an installed snap. The output shows the top-level keys and values, with {...} indicating nested options beneath the current key name level.

```shell
$ sudo snap get nextcloud
Key        Value
mode       production
nextcloud  {...}
php        {...}
ports      {...}
private    {...}

```

--------------------------------

### Enable and disable services with snapctl start/stop

Source: https://snapcraft.io/docs/how-to-guides/snap-development/use-snapctl

Enable a service with --enable when starting, and disable a service with --disable when stopping. Note the typo in the first command (myql instead of mysql).

```bash
$ snapctl start nextcloud.myql --enable
$ snapctl stop nextcloud.mysql --disable

```

--------------------------------

### Test changes to an unpacked snap

Source: https://snapcraft.io/docs/how-to-guides/snap-development/snap-try

Shows how changes to files in the squashfs-root directory are immediately reflected in the installed snap. The example edits the bin/echo script and runs the snap again to see the updated output.

```bash
$ hello-world
Hello world!
$ sed -i 's/World/Everyone/g' /home/user/squashfs-root/bin/echo
$ hello-world
Hello Everyone!

```
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