utils: implement linux distro id detection

The OS probe logic must be able to check a distro programmatically,
add get_linux_distro_id to return an id whitout versioning.
Ensure the availability of 'ubuntu' when we need to ensure certain
features are only used with a supported system.

src/utils/boot.py

@@ -12,7 +12,7 @@ import os
 import shlex
 import subprocess
 
-from src.utils.probe import OSFamily, get_os_family
+from src.utils.probe import OSFamily, get_os_family, get_linux_distro_id, os_probe
 from src.utils.disk import get_partition_device, get_efi_partition
 from src.utils.uefi import *
 from src.utils.fs import *
@@ -23,6 +23,10 @@ def _boot_bios_legacy(disk, part, mountpoint):
 
 def _boot_bios_linux(disk, part, mountpoint):
     logging.info(f'Booting Linux system')
+
+    if not get_linux_distro_id(mountpoint) == 'ubuntu':
+        raise NotImplementedError(f'{os_probe(mountpoint)} detected, only Ubuntu is supported for legacy BIOS boot')
+
     _boot_bios_legacy(disk, part, mountpoint)
 
 def _boot_bios_windows(disk, part, mountpoint):

src/utils/probe.py

@@ -112,6 +112,28 @@ def linux_is64bit(mountpoint):
         return True if bits == '64bit' else False
     return os.path.exists(lib64_path)
 
+def get_linux_distro_id(mountpoint):
+    """
+    Parses a os-release file and fetches the 'ID' key.
+    Check repository documentation at ./ogclient/os-release-ids.txt
+    for a list of the potential strings it might return.
+    If file or key are not found, then returns generic 'linux' string.
+    """
+    osrelease = f'{mountpoint}/etc/os-release'
+
+    try:
+        with open(osrelease, 'r') as f:
+            for line in f:
+                if line.find('=') == -1:
+                    continue
+                key, value = line.split('=')
+                if key == 'ID':
+                    value = value.replace('\n', '')
+                    value = value.strip('"')
+                    return value
+    except FileNotFoundError as e:
+        logging.error(f'os-release file not found at "{osrelease}"')
+    return 'linux'
 
 def cache_probe():
     """