Check for group existence before adding group

scone/default/recipes/linux.py

@@ -21,7 +21,7 @@ from typing import Optional
 
 from scone.default.steps import linux_steps
 from scone.default.utensils.basic_utensils import SimpleExec
-from scone.default.utensils.linux_utensils import GetPasswdEntry
+from scone.default.utensils.linux_utensils import GetGroupEntry, GetPasswdEntry
 from scone.head.head import Head
 from scone.head.kitchen import Kitchen, Preparation
 from scone.head.recipe import Recipe, RecipeContext
@@ -99,14 +99,25 @@ class LinuxGroup(Recipe):
         # acknowledge tracking
         kitchen.get_dependency_tracker()
 
-        result = await kitchen.ut1areq(
-            SimpleExec(["groupadd", self.group_name], "/"), SimpleExec.Result
+        grp_entry = await kitchen.ut1a(
+            GetGroupEntry(self.group_name), GetGroupEntry.Result
         )
 
-        if result.exit_code != 0:
-            raise RuntimeError(
-                "Failed to create group. Error was: " + result.stderr.strip().decode()
+        if grp_entry:
+            logger.warning(
+                "Not updating existing os-group '%s' as it exists already.",
+                self.group_name,
             )
+        else:
+            result = await kitchen.ut1areq(
+                SimpleExec(["groupadd", self.group_name], "/"), SimpleExec.Result
+            )
+
+            if result.exit_code != 0:
+                raise RuntimeError(
+                    "Failed to create group. Error was: "
+                    + result.stderr.strip().decode()
+                )
 
 
 class DeclareLinuxUser(Recipe):

scone/default/utensils/linux_utensils.py

@@ -14,7 +14,7 @@
 #
 #  You should have received a copy of the GNU General Public License
 #  along with Scone.  If not, see <https://www.gnu.org/licenses/>.
-
+import grp
 import pwd
 
 import attr
@@ -50,3 +50,25 @@ class GetPasswdEntry(Utensil):
                 shell=entry.pw_shell,
             )
         )
+
+
+@attr.s(auto_attribs=True)
+class GetGroupEntry(Utensil):
+    group_name: str
+
+    @attr.s(auto_attribs=True)
+    class Result:
+        gid: int
+
+    async def execute(self, channel: Channel, worktop: Worktop):
+        try:
+            entry = grp.getgrnam(self.group_name)
+        except KeyError:
+            await channel.send(None)
+            return
+
+        await channel.send(
+            GetGroupEntry.Result(
+                gid=entry.gr_gid,
+            )
+        )