diff --git a/.travis.yml b/.travis.yml
index c1ec65a13..ea553d96c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -44,7 +44,7 @@ jobs:
       python: "nightly"
 
 install:
-  - pip install coveralls
+  - pip install coveralls pyfakefs
   # add ssh public / private key pair to ensure user can start ssh session to localhost for tests
   - ssh-keygen -b 2048 -t rsa -f /home/travis/.ssh/id_rsa -N ""
   - cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys
diff --git a/CHANGES b/CHANGES
index b971c18b6..98cc82717 100644
--- a/CHANGES
+++ b/CHANGES
@@ -5,6 +5,7 @@ Upcoming Release
 * GUI change: define accelerator keys for menu bar and tabs, as well as toolbar shortcuts (#1104)
 * Desktop integration: update .desktop file to mark Back In Time as a single main window program (#1258)
 * Bugfix: AttributeError in "Diff Options" dialog (#898)
+* Feature: Diagnostic output.
 * Documentation update: correct description of profile<N>.schedule.time in backintime-config manpage (#1270)
 * Translation update: Brazilian Portuguese (#1267)
 * Translation update: Italian (#1110, #1123)
diff --git a/common/diagnostics.py b/common/diagnostics.py
new file mode 100644
index 000000000..c69322f01
--- /dev/null
+++ b/common/diagnostics.py
@@ -0,0 +1,307 @@
+"""short doc
+
+long doc
+
+"""
+import sys
+import os
+import pathlib
+import pwd
+import platform
+import locale
+import subprocess
+import json
+import re
+import config  # config.Config.VERSION  Refactor after src-layout migration
+
+
+def collect_diagnostics():
+    """Collect information's about environment and versions of tools and
+    packages used by Back In Time.
+
+    The informatinos can be used e.g. for debugging and but reports.
+
+    Returns:
+       dict: A nested dictionary.
+    """
+    result = {}
+
+    USER_REPLACED = 'UsernameReplaced'
+
+    pwd_struct = pwd.getpwuid(os.getuid())
+
+    # === BACK IN TIME ===
+    distro_path = _determine_distro_package_folder()
+
+    result['backintime'] = {
+        'name': config.Config.APP_NAME,
+        'version': config.Config.VERSION,
+        'config-version': config.Config.CONFIG_VERSION,
+        'distribution-package': str(distro_path),
+        'started-from': str(pathlib.Path(config.__file__).parent),
+        'running_as_root': pwd_struct.pw_name == 'root',
+    }
+
+    # Git repo
+    git_info = get_git_repository_info(distro_path)
+
+    if git_info:
+
+        for key in git_info:
+            result['backintime'][f'git-{key}'] = git_info[key]
+
+    # == HOST setup ===
+    result['host-setup'] = {
+        # Kernel & Architecture
+        'platform': platform.platform(),
+        # OS Version (and maybe name)
+        'system': '{} {}'.format(platform.system(), platform.version()),
+    }
+
+
+    # content of /etc/os-release
+    try:
+        osrelease = platform.freedesktop_os_release()  # since Python 3.10
+
+    except AttributeError:  # refactor: when we drop Python 3.9 support
+        # read and parse the os-release file ourself
+        fp = pathlib.Path('/etc') / 'os-release'
+
+        try:
+            with fp.open('r') as handle:
+                osrelease = handle.read()
+
+        except FileNotFoundError:
+            osrelease = '(os-release file not found)'
+
+        else:
+            osrelease = re.findall('PRETTY_NAME=\"(.*)\"', osrelease)[0]
+
+    result['host-setup']['os-release'] = osrelease
+
+    # Display system (X11 or Wayland)
+    # This doesn't catch all edge cases.
+    # For more detials see: https://unix.stackexchange.com/q/202891/136851
+    result['host-setup']['display-system'] = os.environ.get(
+        'XDG_SESSION_TYPE', '($XDG_SESSION_TYPE not set)')
+
+    # locale (system language etc)
+    result['host-setup']['locale'] = ', '.join(locale.getlocale())
+
+    # PATH environment variable
+    result['host-setup']['PATH'] = os.environ.get('PATH', '($PATH unknown)')
+
+    # === PYTHON setup ===
+    python = '{} {} {} {}'.format(
+        platform.python_version(),
+        ' '.join(platform.python_build()),
+        platform.python_implementation(),
+        platform.python_compiler()
+    )
+
+    # Python branch and revision if available
+    branch = platform.python_branch()
+    if branch:
+        python = '{} branch: {}'.format(python, branch)
+    rev = platform.python_revision()
+    if rev:
+        python = '{} rev: {}'.format(python, rev)
+
+    result['python-setup'] = {
+        'python': python,
+        'sys.path': sys.path,
+    }
+
+    # Qt
+    try:
+        import PyQt5.QtCore
+    except ImportError:
+        qt = '(Can not import PyQt5)'
+    else:
+        qt = 'PyQt {} / Qt {}'.format(PyQt5.QtCore.PYQT_VERSION_STR,
+                                      PyQt5.QtCore.QT_VERSION_STR)
+    finally:
+        result['python-setup']['qt'] = qt
+
+    # === EXTERN TOOL ===
+    result['external-programs'] = {}
+
+    # rsync
+    # rsync >= 3.2.6: -VV return a json
+    # rsync <= 3.2.5 and > (somewhere near) 3.1.3: -VV return the same as -V
+    # rsync <= (somewhere near) 3.1.3: -VV doesn't exists
+    # rsync == 3.1.3 (Ubuntu 20 LTS) doesn't even know '-V'
+
+    # This work when rsync understand -VV and return json or human readable
+    result['external-programs']['rsync'] = _get_extern_versions(
+        ['rsync', '-VV'],
+        r'rsync  version (.*)  protocol version',
+        try_json=True,
+        error_pattern=r'unknown option'
+    )
+
+    # When -VV was unknown use -V and parse the human readable output
+    if not result['external-programs']['rsync']:
+        # try the old way
+        result['external-programs']['rsync'] = _get_extern_versions(
+            ['rsync', '--version'],
+            r'rsync  version (.*)  protocol version'
+        )
+
+    # ssh
+    result['external-programs']['ssh'] = _get_extern_versions(['ssh', '-V'])
+
+    # sshfs
+    result['external-programs']['sshfs'] \
+        = _get_extern_versions(['sshfs', '-V'], r'SSHFS version (.*)\n')
+
+    # EncFS
+    # Using "[Vv]" in the pattern because encfs does translate its output.
+    # e.g. In German it is "Version" in English "version".
+    result['external-programs']['encfs'] \
+        = _get_extern_versions(['encfs'], r'Build: encfs [Vv]ersion (.*)\n')
+
+    # Shell
+    SHELL_ERR_MSG = '($SHELL not exists)'
+    shell = os.environ.get('SHELL', SHELL_ERR_MSG)
+    result['external-programs']['shell'] = shell
+
+    if shell != SHELL_ERR_MSG:
+        shell_version = _get_extern_versions([shell, '--version'])
+        result['external-programs']['shell-version'] = shell_version.split('\n')[0]
+
+    result = json.loads(
+        json.dumps(result).replace(pwd_struct.pw_name, USER_REPLACED)
+    )
+
+    return result
+
+
+def _get_extern_versions(cmd,
+                         pattern=None,
+                         try_json=False,
+                         error_pattern=None):
+    """Get the version of an external tools using ``subprocess.Popen()``.
+
+    Args:
+        cmd (list): Commandline arguments that will be passed to `Popen()`.
+        pattern (str): A regex pattern to extract the version string from the
+                       commands output.
+        try_json (bool): Interpet the output as json first (default: False).
+        error_pattern (str): Regex pattern to identify a message in the output
+                             that indicates an error.
+
+    """
+
+    try:
+        # as context manager to prevent ResourceWarning's
+        with subprocess.Popen(cmd,
+                              stdout=subprocess.PIPE,
+                              stderr=subprocess.PIPE,
+                              universal_newlines=True) as proc:
+            error_output = proc.stderr.read()
+            std_output = proc.stdout.read()
+
+    except FileNotFoundError:
+        result = f'(no {cmd[0]})'
+
+    else:
+        # Check for errors
+        if error_pattern:
+            match = re.findall(error_pattern, error_output)
+
+            if match:
+                return None
+
+        # some tools use "stderr" for version infos
+        if not std_output:
+            result = error_output
+        else:
+            result = std_output
+
+        # Expect JSON string
+        if try_json:
+
+            try:
+                result = json.loads(result)
+
+            except json.decoder.JSONDecodeError:
+                # Wasn't a json. Try regex in the next block.
+                pass
+
+            else:
+                # No regex parsing because it was json
+                pattern = None
+
+        # extract version string
+        if pattern:
+            result = re.findall(pattern, result)[0]
+
+    return result.strip()
+
+
+def get_git_repository_info(path=None):
+    """Return the current branch and last commit hash.
+
+    Credits: https://stackoverflow.com/a/51224861/4865723
+
+    Args:
+        path (pathlib.Path): Path with '.git' folder in (default is
+                             current working directory).
+
+    Returns:
+        (dict): Dict with keys "branch" and "hash" if it is a git repo,
+                otherwise an `None`.
+    """
+
+    if not path:
+        path = pathlib.Path.cwd()
+
+    git_folder = path / '.git'
+
+    if not git_folder.exists():
+        return None
+
+    result = {}
+
+    # branch name
+    with (git_folder / 'HEAD').open('r') as handle:
+        val = handle.read()
+
+    if val.startswith('ref: '):
+        result['branch'] = '/'.join(val.split('/')[2:]).strip()
+
+    else:
+        result['branch'] = '(detached HEAD)'
+        result['hash'] = val
+
+        return result
+
+    # commit hash
+    with (git_folder / 'refs' / 'heads' / result['branch']) \
+         .open('r') as handle:
+        result['hash'] = handle.read().strip()
+
+    return result
+
+
+def _determine_distro_package_folder():
+    """Return the projects root folder.
+
+    In Python terms it is the "Distribution Package" not the "Modules
+    Package".
+
+    Development info: The function become obslet when migrating the project
+    to the "src" layout.
+    """
+
+    # "current" folder
+    path = pathlib.Path(__file__)
+
+    # level of highest folder named "backintime"
+    bit_idx = path.parts.index('backintime')
+
+    # cut the path to that folder
+    path = pathlib.Path(*(path.parts[:bit_idx+1]))
+
+    return path
diff --git a/common/test/test_diagnostics.py b/common/test/test_diagnostics.py
new file mode 100644
index 000000000..f5ad0511b
--- /dev/null
+++ b/common/test/test_diagnostics.py
@@ -0,0 +1,127 @@
+import sys
+import pathlib
+import unittest
+import pyfakefs.fake_filesystem_unittest as pyfakefs_ut
+
+# This workaround will become obsolet when migrating to src-layout
+sys.path.append(str(pathlib.Path(__file__).parent))
+import diagnostics  # testing target
+
+
+class Diagnostics(unittest.TestCase):
+    """
+    """
+
+    def test_minimal(self):
+        """Minimal set of elements."""
+
+        result = diagnostics.collect_diagnostics()
+
+        # 1st level keys
+        self.assertEqual(
+            sorted(result.keys()),
+            ['backintime', 'external-programs', 'host-setup', 'python-setup']
+        )
+
+        # 2nd level "backintime"
+        minimal_keys = ['name', 'version', 'config-version',
+                        'started-from', 'running_as_root']
+        for key in minimal_keys:
+            self.assertIn(key, result['backintime'], key)
+
+        # 2nd level "host-setup"
+        minimal_keys = ['platform', 'system', 'display-system',
+                        'locale', 'PATH']
+        for key in minimal_keys:
+            self.assertIn(key, result['host-setup'], key)
+
+        # 2nd level "python-setup"
+        self.assertIn('python', result['python-setup'], 'python')
+
+        # 2nd level "external-programs"
+        minimal_keys = ['rsync', 'shell']
+        for key in minimal_keys:
+            self.assertIn(key, result['external-programs'], key)
+
+
+    def test_no_ressource_warning(self):
+        """No ResourceWarning's.
+
+        Using subprocess.Popen() often cause ResourceWarning's when not used
+        as a context manaager.
+        """
+
+        # an AssertionError must be raised! See next block for explanation.
+        with self.assertRaises(AssertionError):
+
+            # We expect NO ResourceWarnings. But Python doesn't offer
+            # assertNoWarns().
+            # This will raise an AssertionError bcause no ResourceWarning's
+            # are raised.
+            with self.assertWarns(ResourceWarning):
+
+                diagnostics.collect_diagnostics()
+
+    def test_no_extern_version(self):
+        """Get version from not existing tool.
+        """
+        self.assertEqual(
+            diagnostics._get_extern_versions(['fooXbar']),
+            '(no fooXbar)'
+        )
+
+
+class Diagnostics_FakeFS(pyfakefs_ut.TestCase):
+    """Tests using a fake filesystem.
+    """
+
+    def setUp(self):
+        self.setUpPyfakefs(allow_root_user=False)
+
+    def test_distro_package_folder(self):
+        """Determin the folder of the project.
+        """
+
+        # real path
+        path = pathlib.Path(diagnostics.__file__)
+
+        # replicate that path in the fake fileystem
+        path.mkdir(parents=True)
+        path.touch()
+
+        result = diagnostics._determine_distro_package_folder()
+
+        self.assertEqual(result, path.parent.parent)
+
+    def test_git_repo_info(self):
+        """
+        """
+
+        # not a git repo
+        self.assertEqual(diagnostics.get_git_repository_info(), None)
+
+        # simulate a git repo
+        path = pathlib.Path('.git')
+        path.mkdir()
+
+        # Branch folders and hash containing file
+        foobar = path / 'refs' / 'heads' / 'fix' / 'foobar'
+        foobar.parent.mkdir(parents=True)
+
+        with foobar.open('w') as handle:
+            handle.write('01234')
+
+        # HEAD file
+        head = path / 'HEAD'
+
+        with head.open('w') as handle:
+            handle.write('ref: refs/heads/fix/foobar')
+
+        # Test
+        self.assertEqual(
+            diagnostics.get_git_repository_info(),
+            {
+                'hash': '01234',
+                'branch': 'fix/foobar'
+            }
+        )