Remove Ubuntu 18.04 and 20.04 support (#664)

Both versions are end-of-life. Only 22.04 and 24.04 are supported.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: retlehs

README.md

@@ -228,7 +228,7 @@ Current supported settings:
 | Setting | Description | Type | Default |
 | --- | --- | -- | -- |
 | `manager` | VM manager (Options: `auto` (depends on OS), `lima`)| string | "auto" |
-| `ubuntu` | Ubuntu OS version (Options: `18.04`, `20.04`, `22.04`, `24.04`)| string |
+| `ubuntu` | Ubuntu OS version (Options: `22.04`, `24.04`)| string |
 | `hosts_resolver` | VM hosts resolver (Options: `hosts_file`)| string |
 | `instance_name` | Custom name for the VM instance | string | First site name alphabetically |
 | `images` | Custom OS image | object | Set based on `ubuntu` version |

cli_config/cli_config.go

@@ -66,8 +66,8 @@ func (c *Config) LoadFile(path string) error {
 		return fmt.Errorf("%w: unsupported value for `vm.manager`. Must be one of: auto, lima", InvalidConfigErr)
 	}
 
-	if c.Vm.Ubuntu != "" && c.Vm.Ubuntu != "18.04" && c.Vm.Ubuntu != "20.04" && c.Vm.Ubuntu != "22.04" && c.Vm.Ubuntu != "24.04" {
-		return fmt.Errorf("%w: unsupported value for `vm.ubuntu`. Must be one of: 18.04, 20.04, 22.04, 24.04", InvalidConfigErr)
+	if c.Vm.Ubuntu != "" && c.Vm.Ubuntu != "22.04" && c.Vm.Ubuntu != "24.04" {
+		return fmt.Errorf("%w: unsupported value for `vm.ubuntu`. Must be one of: 22.04, 24.04", InvalidConfigErr)
 	}
 
 	if c.Vm.HostsResolver != "" && c.Vm.HostsResolver != "hosts_file" {

pkg/lima/manager_test.go

@@ -127,7 +127,7 @@ func TestNewInstanceUbuntuVersion(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	trellis.CliConfig.Vm.Ubuntu = "20.04"
+	trellis.CliConfig.Vm.Ubuntu = "22.04"
 
 	t.Setenv("TRELLIS_BYPASS_LIMA_REQUIREMENTS", "1")
 
@@ -152,8 +152,8 @@ func TestNewInstanceUbuntuVersion(t *testing.T) {
 		t.Errorf("expected instance config to have 2 images, got %d", len(instance.Config.Images))
 	}
 
-	if instance.Config.Images[0].Alias != "focal" {
-		t.Errorf("expected instance config to have focal image, got %q", instance.Config.Images[0].Alias)
+	if instance.Config.Images[0].Alias != "jammy" {
+		t.Errorf("expected instance config to have jammy image, got %q", instance.Config.Images[0].Alias)
 	}
 
 	if len(instance.Config.PortForwards) != 1 {

pkg/lima/ubuntu.go

@@ -1,30 +1,6 @@
 package lima
 
 var UbuntuImages = map[string][]Image{
-	"18.04": {
-		{
-			Alias:    "bionic",
-			Location: "https://cloud-images.ubuntu.com/bionic/current/bionic-server-cloudimg-amd64.img",
-			Arch:     "x86_64",
-		},
-		{
-			Alias:    "bionic",
-			Location: "https://cloud-images.ubuntu.com/bionic/current/bionic-server-cloudimg-arm64.img",
-			Arch:     "aarch64",
-		},
-	},
-	"20.04": {
-		{
-			Alias:    "focal",
-			Location: "https://cloud-images.ubuntu.com/focal/current/focal-server-cloudimg-amd64.img",
-			Arch:     "x86_64",
-		},
-		{
-			Alias:    "focal",
-			Location: "https://cloud-images.ubuntu.com/focal/current/focal-server-cloudimg-arm64.img",
-			Arch:     "aarch64",
-		},
-	},
 	"22.04": {
 		{
 			Alias:    "jammy",