nixos/users: Increase maximum system uid/gid from 499 to 999

This enlarges the system uid/gid range 6-fold, from 100 to 600 ids. This
is a preventative measure against running out of dynamically allocated
ids for NixOS services with isSystemUser, which should become the
preferred way of allocating uids for non-real users.

nixos/modules/config/update-users-groups.pl

@@ -56,12 +56,12 @@ sub allocGid {
         $gidsUsed{$prevGid} = 1;
         return $prevGid;
     }
-    return allocId(\%gidsUsed, \%gidsPrevUsed, 400, 499, 0, sub { my ($gid) = @_; getgrgid($gid) });
+    return allocId(\%gidsUsed, \%gidsPrevUsed, 400, 999, 0, sub { my ($gid) = @_; getgrgid($gid) });
 }
 
 sub allocUid {
     my ($name, $isSystemUser) = @_;
-    my ($min, $max, $up) = $isSystemUser ? (400, 499, 0) : (1000, 29999, 1);
+    my ($min, $max, $up) = $isSystemUser ? (400, 999, 0) : (1000, 29999, 1);
     my $prevUid = $uidMap->{$name};
     if (defined $prevUid && $prevUid >= $min && $prevUid <= $max && !defined $uidsUsed{$prevUid}) {
         print STDERR "reviving user '$name' with UID $prevUid\n";

nixos/modules/programs/shadow.nix

@@ -6,17 +6,27 @@ with lib;
 
 let
 
+  /*
+  There are three different sources for user/group id ranges, each of which gets
+  used by different programs:
+  - The login.defs file, used by the useradd, groupadd and newusers commands
+  - The update-users-groups.pl file, used by NixOS in the activation phase to
+    decide on which ids to use for declaratively defined users without a static
+    id
+  - Systemd compile time options -Dsystem-uid-max= and -Dsystem-gid-max=, used
+    by systemd for features like ConditionUser=@system and systemd-sysusers
+  */
   loginDefs =
     ''
       DEFAULT_HOME yes
 
       SYS_UID_MIN  400
-      SYS_UID_MAX  499
+      SYS_UID_MAX  999
       UID_MIN      1000
       UID_MAX      29999
 
       SYS_GID_MIN  400
-      SYS_GID_MAX  499
+      SYS_GID_MAX  999
       GID_MIN      1000
       GID_MAX      29999
 

pkgs/os-specific/linux/systemd/default.nix

@@ -84,8 +84,18 @@ stdenv.mkDerivation {
     "-Dldconfig=false"
     "-Dsmack=true"
     "-Db_pie=true"
-    "-Dsystem-uid-max=499" #TODO: debug why awking around in /etc/login.defs doesn't work
-    "-Dsystem-gid-max=499"
+    /*
+    As of now, systemd doesn't allow runtime configuration of these values. So
+    the settings in /etc/login.defs have no effect on it. Many people think this
+    should be supported however, see
+    - https://github.com/systemd/systemd/issues/3855
+    - https://github.com/systemd/systemd/issues/4850
+    - https://github.com/systemd/systemd/issues/9769
+    - https://github.com/systemd/systemd/issues/9843
+    - https://github.com/systemd/systemd/issues/10184
+    */
+    "-Dsystem-uid-max=999"
+    "-Dsystem-gid-max=999"
     # "-Dtime-epoch=1"
 
     (if !stdenv.hostPlatform.isEfi then "-Dgnu-efi=false" else "-Dgnu-efi=true")