nixos/munge: run munge as user munge instead of root. (#41509)

* Added a note in release notes (incompatibilities)
* Adapt slurm test
* Change user to munge in service.munge

nixos/modules/services/security/munge.nix

@@ -35,7 +35,15 @@ in
 
     environment.systemPackages = [ pkgs.munge ];
 
-    systemd.services.munged = { 
+    users.users.munge = {
+      description   = "Munge daemon user";
+      isSystemUser  = true;
+      group         = "munge";
+    };
+
+    users.groups.munge = {};
+
+    systemd.services.munged = {
       wantedBy = [ "multi-user.target" ];
       after = [ "network.target" ];
 
@@ -44,14 +52,20 @@ in
       preStart = ''
         chmod 0700 ${cfg.password}
         mkdir -p /var/lib/munge -m 0711
+        chown -R munge:munge /var/lib/munge
         mkdir -p /var/log/munge -m 0700
+        chown -R munge:munge /var/log/munge
         mkdir -p /run/munge -m 0755
+        chown -R munge:munge /run/munge
       '';
 
       serviceConfig = {
         ExecStart = "${pkgs.munge}/bin/munged --syslog --key-file ${cfg.password}";
         PIDFile = "/run/munge/munged.pid";
         ExecReload = "${pkgs.coreutils}/bin/kill -HUP $MAINPID";
+        PermissionsStartOnly = "true";
+        User = "munge";
+        Group = "munge";
       };
 
     };