Trees and Data

A snapshot references a tree by the SHA-256 hash of the JSON string representation of its contents. Trees and data are saved in pack files in a subdirectory of the directory data.

The command restic cat blob can be used to inspect the tree referenced above (piping the output of the command to jq . so that the JSON is indented):

$ restic -r /tmp/restic-repo cat blob 2da81727b6585232894cfbb8f8bdab8d1eccd3d8f7c92bc934d62e62e618ffdf | jq .
enter password for repository:

{
    "nodes": [
        {
            "name": "testdata",
            "type": "dir",
            "mode": 493,
            "mtime": "2014-12-22T14:47:59.912418701+01:00",
            "atime": "2014-12-06T17:49:21.748468803+01:00",
            "ctime": "2014-12-22T14:47:59.912418701+01:00",
            "uid": 1000,
            "gid": 100,
            "user": "fd0",
            "inode": 409704562,
            "content": null,
            "subtree": "b26e315b0988ddcd1cee64c351d13a100fedbc9fdbb144a67d1b765ab280b4dc"
        }
    ]
}

A tree contains a list of entries (in the field nodes) which contain meta data like a name and timestamps. When the entry references a directory, the field subtree contains the plain text ID of another tree object.

When the command restic cat blob is used, the plaintext ID is needed to print a tree. The tree referenced above can be dumped as follows:

$ restic -r /tmp/restic-repo cat blob b26e315b0988ddcd1cee64c351d13a100fedbc9fdbb144a67d1b765ab280b4dc
enter password for repository:

{
    "nodes": [
      {
        "name": "testfile",
        "type": "file",
        "mode": 420,
        "mtime": "2014-12-06T17:50:23.34513538+01:00",
        "atime": "2014-12-06T17:50:23.338468713+01:00",
        "ctime": "2014-12-06T17:50:23.34513538+01:00",
        "uid": 1000,
        "gid": 100,
        "user": "fd0",
        "inode": 416863351,
        "size": 1234,
        "links": 1,
        "content": [
          "50f77b3b4291e8411a027b9f9b9e64658181cc676ce6ba9958b95f268cb1109d"
        ]
      },
      [...]
    ]
}

This tree contains a file entry. This time, the subtree field is not present and the content field contains a list with one plain text SHA-256 hash.

The command restic cat blob can also be used to extract and decrypt data given a plaintext ID, e.g. for the data mentioned above:

$ restic -r /tmp/restic-repo cat blob 50f77b3b4291e8411a027b9f9b9e64658181cc676ce6ba9958b95f268cb1109d | sha256sum
enter password for repository:
50f77b3b4291e8411a027b9f9b9e64658181cc676ce6ba9958b95f268cb1109d  -

As can be seen from the output of the program sha256sum, the hash matches the plaintext hash from the map included in the tree above, so the correct data has been returned.