···

       
21
       
 
       
and the actions to switch to the new system are calculated. This process takes

     

       
22
       
 
       
two data sources into account: `/etc/fstab` and the current systemd status.

     

       
23
       
 
       
Mounts and swaps are read from `/etc/fstab` and the corresponding actions are

     

       
24
       
-
       
generated. If a new mount is added, for example, the proper `.mount` unit is

     

       
25
       
-
       
marked to be started. The current systemd state is inspected, the difference

     

       
0
       
 
       

     

       
26
       
 
       
between the current system and the desired configuration is calculated and

     

       
27
       
 
       
actions are generated to get to this state. There are a lot of nuances that can

     

       
28
       
 
       
be controlled by the units which are explained here.

     

···

       
21
       
 
       
and the actions to switch to the new system are calculated. This process takes

     

       
22
       
 
       
two data sources into account: `/etc/fstab` and the current systemd status.

     

       
23
       
 
       
Mounts and swaps are read from `/etc/fstab` and the corresponding actions are

     

       
24
       
+
       
generated. If the options of a mount are modified, for example, the proper `.mount`

     

       
25
       
+
       
unit is reloaded (or restarted if anything else changed and it's neither the root

     

       
26
       
+
       
mount or the nix store). The current systemd state is inspected, the difference

     

       
27
       
 
       
between the current system and the desired configuration is calculated and

     

       
28
       
 
       
actions are generated to get to this state. There are a lot of nuances that can

     

       
29
       
 
       
be controlled by the units which are explained here.

     

···

       
661
       
 
       
        # Filesystem entry disappeared, so unmount it.

     

       
662
       
 
       
        $units_to_stop{$unit} = 1;

     

       
663
       
 
       
    } elsif ($cur->{fsType} ne $new->{fsType} || $cur->{device} ne $new->{device}) {

     

       
664
       
-
       
        # Filesystem type or device changed, so unmount and mount it.

     

       
665
       
-
       
        $units_to_stop{$unit} = 1;

     

       
666
       
-
       
        $units_to_start{$unit} = 1;

     

       
667
       
-
       
        record_unit($start_list_file, $unit);

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
668
       
 
       
    } elsif ($cur->{options} ne $new->{options}) {

     

       
669
       
 
       
        # Mount options changes, so remount it.

     

       
670
       
 
       
        $units_to_reload{$unit} = 1;

     

···

       
661
       
 
       
        # Filesystem entry disappeared, so unmount it.

     

       
662
       
 
       
        $units_to_stop{$unit} = 1;

     

       
663
       
 
       
    } elsif ($cur->{fsType} ne $new->{fsType} || $cur->{device} ne $new->{device}) {

     

       
664
       
+
       
        if ($mount_point eq '/' or $mount_point eq '/nix') {

     

       
665
       
+
       
            if ($cur->{options} ne $new->{options}) {

     

       
666
       
+
       
                # Mount options changed, so remount it.

     

       
667
       
+
       
                $units_to_reload{$unit} = 1;

     

       
668
       
+
       
                record_unit($reload_list_file, $unit);

     

       
669
       
+
       
            } else {

     

       
670
       
+
       
                # Don't unmount / or /nix if the device changed

     

       
671
       
+
       
                $units_to_skip{$unit} = 1;

     

       
672
       
+
       
            }

     

       
673
       
+
       
        } else {

     

       
674
       
+
       
            # Filesystem type or device changed, so unmount and mount it.

     

       
675
       
+
       
            $units_to_restart{$unit} = 1;

     

       
676
       
+
       
            record_unit($restart_list_file, $unit);

     

       
677
       
+
       
        }

     

       
678
       
 
       
    } elsif ($cur->{options} ne $new->{options}) {

     

       
679
       
 
       
        # Mount options changes, so remount it.

     

       
680
       
 
       
        $units_to_reload{$unit} = 1;

     

···

       
66
       
 
       
          # Hello world!

     

       
67
       
 
       
        '';

     

       
68
       
 
       


     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
69
       
 
       
        simpleService.configuration = {

     

       
70
       
 
       
          systemd.services.test = {

     

       
71
       
 
       
            wantedBy = [ "multi-user.target" ];

     
···

       
671
       
 
       
        machine.succeed("echo dbus.service > /run/nixos/start-list")

     

       
672
       
 
       
        out = switch_to_specialisation("${machine}", "modifiedSystemConf")

     

       
673
       
 
       
        assert_contains(out, "starting the following units: dbus.service\n")

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
674
       
 
       


     

       
675
       
 
       
    with subtest("services"):

     

       
676
       
 
       
        switch_to_specialisation("${machine}", "")

     

···

       
66
       
 
       
          # Hello world!

     

       
67
       
 
       
        '';

     

       
68
       
 
       


     

       
69
       
+
       
        addedMount.configuration.virtualisation.fileSystems."/test" = {

     

       
70
       
+
       
          device = "tmpfs";

     

       
71
       
+
       
          fsType = "tmpfs";

     

       
72
       
+
       
        };

     

       
73
       
+
       


     

       
74
       
+
       
        addedMountOptsModified.configuration = {

     

       
75
       
+
       
          imports = [ addedMount.configuration ];

     

       
76
       
+
       
          virtualisation.fileSystems."/test".options = [ "x-test" ];

     

       
77
       
+
       
        };

     

       
78
       
+
       


     

       
79
       
+
       
        addedMountDevModified.configuration = {

     

       
80
       
+
       
          imports = [ addedMountOptsModified.configuration ];

     

       
81
       
+
       
          virtualisation.fileSystems."/test".device = lib.mkForce "ramfs";

     

       
82
       
+
       
        };

     

       
83
       
+
       


     

       
84
       
+
       
        storeMountModified.configuration = {

     

       
85
       
+
       
          virtualisation.fileSystems."/".device = lib.mkForce "auto";

     

       
86
       
+
       
        };

     

       
87
       
+
       


     

       
88
       
 
       
        simpleService.configuration = {

     

       
89
       
 
       
          systemd.services.test = {

     

       
90
       
 
       
            wantedBy = [ "multi-user.target" ];

     
···

       
690
       
 
       
        machine.succeed("echo dbus.service > /run/nixos/start-list")

     

       
691
       
 
       
        out = switch_to_specialisation("${machine}", "modifiedSystemConf")

     

       
692
       
 
       
        assert_contains(out, "starting the following units: dbus.service\n")

     

       
693
       
+
       


     

       
694
       
+
       
    with subtest("fstab mounts"):

     

       
695
       
+
       
        switch_to_specialisation("${machine}", "")

     

       
696
       
+
       
        # add a mountpoint

     

       
697
       
+
       
        out = switch_to_specialisation("${machine}", "addedMount")

     

       
698
       
+
       
        assert_lacks(out, "stopping the following units:")

     

       
699
       
+
       
        assert_lacks(out, "NOT restarting the following changed units:")

     

       
700
       
+
       
        assert_lacks(out, "\nrestarting the following units:")

     

       
701
       
+
       
        assert_lacks(out, "\nstarting the following units:")

     

       
702
       
+
       
        assert_contains(out, "the following new units were started: test.mount\n")

     

       
703
       
+
       
        # modify the mountpoint's options

     

       
704
       
+
       
        out = switch_to_specialisation("${machine}", "addedMountOptsModified")

     

       
705
       
+
       
        assert_lacks(out, "stopping the following units:")

     

       
706
       
+
       
        assert_lacks(out, "NOT restarting the following changed units:")

     

       
707
       
+
       
        assert_contains(out, "reloading the following units: test.mount\n")

     

       
708
       
+
       
        assert_lacks(out, "\nrestarting the following units:")

     

       
709
       
+
       
        assert_lacks(out, "\nstarting the following units:")

     

       
710
       
+
       
        assert_lacks(out, "the following new units were started:")

     

       
711
       
+
       
        # modify the device

     

       
712
       
+
       
        out = switch_to_specialisation("${machine}", "addedMountDevModified")

     

       
713
       
+
       
        assert_lacks(out, "stopping the following units:")

     

       
714
       
+
       
        assert_lacks(out, "NOT restarting the following changed units:")

     

       
715
       
+
       
        assert_lacks(out, "reloading the following units:")

     

       
716
       
+
       
        assert_contains(out, "\nrestarting the following units: test.mount\n")

     

       
717
       
+
       
        assert_lacks(out, "\nstarting the following units:")

     

       
718
       
+
       
        assert_lacks(out, "the following new units were started:")

     

       
719
       
+
       
        # modify both

     

       
720
       
+
       
        out = switch_to_specialisation("${machine}", "addedMount")

     

       
721
       
+
       
        assert_lacks(out, "stopping the following units:")

     

       
722
       
+
       
        assert_lacks(out, "NOT restarting the following changed units:")

     

       
723
       
+
       
        assert_lacks(out, "reloading the following units:")

     

       
724
       
+
       
        assert_contains(out, "\nrestarting the following units: test.mount\n")

     

       
725
       
+
       
        assert_lacks(out, "\nstarting the following units:")

     

       
726
       
+
       
        assert_lacks(out, "the following new units were started:")

     

       
727
       
+
       
        # remove the mount

     

       
728
       
+
       
        out = switch_to_specialisation("${machine}", "")

     

       
729
       
+
       
        assert_contains(out, "stopping the following units: test.mount\n")

     

       
730
       
+
       
        assert_lacks(out, "NOT restarting the following changed units:")

     

       
731
       
+
       
        assert_contains(out, "reloading the following units: dbus.service\n")

     

       
732
       
+
       
        assert_lacks(out, "\nrestarting the following units:")

     

       
733
       
+
       
        assert_lacks(out, "\nstarting the following units:")

     

       
734
       
+
       
        assert_lacks(out, "the following new units were started:")

     

       
735
       
+
       
        # change something about the / mount

     

       
736
       
+
       
        out = switch_to_specialisation("${machine}", "storeMountModified")

     

       
737
       
+
       
        assert_lacks(out, "stopping the following units:")

     

       
738
       
+
       
        assert_contains(out, "NOT restarting the following changed units: -.mount")

     

       
739
       
+
       
        assert_contains(out, "reloading the following units: dbus.service\n")

     

       
740
       
+
       
        assert_lacks(out, "\nrestarting the following units:")

     

       
741
       
+
       
        assert_lacks(out, "\nstarting the following units:")

     

       
742
       
+
       
        assert_lacks(out, "the following new units were started:")

     

       
743
       
 
       


     

       
744
       
 
       
    with subtest("services"):

     

       
745
       
 
       
        switch_to_specialisation("${machine}", "")