How to build, install and use the snapshot-exclude-demo snap:

Install snapcraft, lxd and git

sudo snap install snapcraft --classic
sudo snap install lxd
sudo apt update
sudo apt install -y git

Clone repo

cd ~/
git clone https://github.com/ernestl/snapshot-exclude-demo.git

Build the snapshot-exclude-demo snap in lxd container

cd ~/snapshot-exclude-demo
snapcraft --use-lxd --debug

Install the snap (note: this is a development mode snap)

sudo snap install snapshot-exclude-demo_0.1_amd64.snap --devmode --dangerous

ⓘ This snap uses devmode confinement as specified in snapcraft.yaml top-level metadata

Inspect the content of the snap

unsquashfs -f snapshot-exclude-demo_0.1_amd64.snap
tree squashfs-root

This shows the optional metadata file snapshots.yaml installed into the snap meta directory:

squashfs-root
├── bin
│   ├── bash.sh
│   ├── create-system-data.sh
│   └── create-user-data.sh
└── meta
    ├── gui
    ├── snapshots.yaml
    └── snap.yaml

Run the snap bash application to create directories $SNAP_USER_COMMON and $SNAP_USER_DATA and exit

snapshot-exclude-demo.bash

and exit

exit

Create the system data for the test case as super user (required)

sudo snapshot-exclude-demo.create-system-data

This creates the following system data in /var/snap/snapshot-exclude-demo/:

├── common
│   └── generic
│       └── file.dat
├── current -> x1
└── x1
    ├── excl-1
    │   └── file.log
    ├── excl-2
    │   └── file.log
    └── state-info
        └── state.dat

Create the user data for the test case

snapshot-exclude-demo.create-user-data

This creates the following user data in ~/snap/snapshot-exclude-demo/:

├── common
│   ├── generic
│   │   └── file.dat
│   └── tmp
│       └── file.tmp
├── current -> x1
└── x1
    └── large-files
        ├── large-file-not-used.bin
        ├── large-file-not-used.dat
        └── large-file-used.bin

Take a snapshot

snap save snapshot-exclude-demo

ⓘ Take note of the set ID provided on completion of the snap save command

Restore the snapshot

snap restore <set ID>

This restores the system data that was not excluded from the snapshot in /var/snap/snapshot-exclude-demo/:

├── common
│   └── generic
│       └── file.dat
├── current -> x1
└── x1
    └── state-info
        └── state.dat

as well as the user data that was not excluded from the snapshot in ~/snap/snapshot-exclude-demo/:

├── common
│   └── generic
│       └── file.dat
├── current -> x1
└── x1
    └── large-files
        └── large-file-used.bin

Diagram illustrating the snapshot data exclusion during the save and restore actions: