diff -Nru shadow-4.8.1/debian/changelog shadow-4.8.1/debian/changelog
--- shadow-4.8.1/debian/changelog	2021-06-17 21:35:15.000000000 +0200
+++ shadow-4.8.1/debian/changelog	2021-12-16 20:19:44.000000000 +0100
@@ -1,3 +1,10 @@
+shadow (1:4.8.1-1ubuntu9+mvo2) impish; urgency=medium
+
+  * 1017_extrausers_group.patch:
+    - add usermod autodetection of extrausers on ubuntu-core
+
+ -- Michael Vogt <michael.vogt@ubuntu.com>  Thu, 16 Dec 2021 20:19:44 +0100
+
 shadow (1:4.8.1-1ubuntu9) impish; urgency=medium
 
   * Disallow purely numeric usernames. This includes hexadecimal and
diff -Nru shadow-4.8.1/debian/patches/1017_extrausers_group.patch shadow-4.8.1/debian/patches/1017_extrausers_group.patch
--- shadow-4.8.1/debian/patches/1017_extrausers_group.patch	1970-01-01 01:00:00.000000000 +0100
+++ shadow-4.8.1/debian/patches/1017_extrausers_group.patch	2021-12-16 20:19:44.000000000 +0100
@@ -0,0 +1,47 @@
+Index: shadow-4.8.1/src/usermod.c
+===================================================================
+--- shadow-4.8.1.orig/src/usermod.c
++++ shadow-4.8.1/src/usermod.c
+@@ -1636,6 +1636,12 @@ static void open_files (void)
+ 		 * group entries.
+ 		 */
+ 		if (gr_lock () == 0) {
++                        if (try_extrausers) {
++                               gr_setdbname (EXTRAUSERS_GROUP_FILE);
++                               sgr_setdbname (EXTRAUSERS_SHADOWGROUP_FILE);
++                               open_files ();
++                               return;
++                        }
+ 			fprintf (stderr,
+ 			         _("%s: cannot lock %s; try again later.\n"),
+ 			         Prog, gr_dbname ());
+@@ -1643,6 +1649,14 @@ static void open_files (void)
+ 		}
+ 		gr_locked = true;
+ 		if (gr_open (O_CREAT | O_RDWR) == 0) {
++                        if (try_extrausers) {
++                               gr_unlock ();
++                               gr_locked = false;
++                               gr_setdbname (EXTRAUSERS_GROUP_FILE);
++                               sgr_setdbname (EXTRAUSERS_SHADOWGROUP_FILE);
++                               open_files ();
++                               return;
++                        }
+ 			fprintf (stderr,
+ 			         _("%s: cannot open %s\n"),
+ 			         Prog, gr_dbname ());
+@@ -1650,6 +1664,14 @@ static void open_files (void)
+ 		}
+ #ifdef SHADOWGRP
+ 		if (is_shadow_grp && (sgr_lock () == 0)) {
++                        if (try_extrausers) {
++                               gr_unlock ();
++                               gr_locked = false;
++                               gr_setdbname (EXTRAUSERS_GROUP_FILE);
++                               sgr_setdbname (EXTRAUSERS_SHADOWGROUP_FILE);
++                               open_files ();
++                               return;
++                        }
+ 			fprintf (stderr,
+ 			         _("%s: cannot lock %s; try again later.\n"),
+ 			         Prog, sgr_dbname ());
diff -Nru shadow-4.8.1/debian/patches/series shadow-4.8.1/debian/patches/series
--- shadow-4.8.1/debian/patches/series	2020-12-02 11:44:02.000000000 +0100
+++ shadow-4.8.1/debian/patches/series	2021-12-16 20:09:56.000000000 +0100
@@ -21,3 +21,4 @@
 1014_extrausers_delgroup.patch
 1015_add_zsys_support.patch
 1016_extrausers_gpasswd.patch
+1017_extrausers_group.patch