add linux build tags to restrict compilation to linux targets

errors.go

@@ -1,3 +1,5 @@
+//go:build linux
+
 package systemctl
 
 import (

helpers.go

@@ -1,8 +1,11 @@
+//go:build linux
+
 package systemctl
 
 import (
 	"context"
 	"errors"
+	"os"
 	"strconv"
 	"strings"
 	"time"
@@ -55,6 +58,34 @@ func GetPID(ctx context.Context, unit string, opts Options) (int, error) {
 	return strconv.Atoi(value)
 }
 
+func GetUnits(ctx context.Context, opts Options) ([]Unit, error) {
+	args := []string{"list-units", "--all", "--no-legend", "--full", "--no-pager"}
+	if opts.UserMode {
+		args = append(args, "--user")
+	}
+	stdout, stderr, _, err := execute(ctx, args)
+	if err != nil {
+		return []Unit{}, errors.Join(err, filterErr(stderr))
+	}
+	lines := strings.Split(stdout, "\n")
+	units := []Unit{}
+	for _, line := range lines {
+		entry := strings.Fields(line)
+		if len(entry) < 4 {
+			continue
+		}
+		unit := Unit{
+			Name:        entry[0],
+			Load:        entry[1],
+			Active:      entry[2],
+			Sub:         entry[3],
+			Description: strings.Join(entry[4:], " "),
+		}
+		units = append(units, unit)
+	}
+	return units, nil
+}
+
 func GetMaskedUnits(ctx context.Context, opts Options) ([]string, error) {
 	args := []string{"list-unit-files", "--state=masked"}
 	if opts.UserMode {
@@ -84,6 +115,15 @@ func GetMaskedUnits(ctx context.Context, opts Options) ([]string, error) {
 	return units, nil
 }
 
+// check if systemd is the current init system
+func IsSystemd() (bool, error) {
+	b, err := os.ReadFile("/proc/1/comm")
+	if err != nil {
+		return false, err
+	}
+	return strings.TrimSpace(string(b)) == "systemd", nil
+}
+
 // check if a service is masked
 func IsMasked(ctx context.Context, unit string, opts Options) (bool, error) {
 	units, err := GetMaskedUnits(ctx, opts)

helpers_test.go

@@ -238,6 +238,54 @@ func TestGetMemoryUsage(t *testing.T) {
 	})
 }
 
+func TestGetUnits(t *testing.T) {
+	type testCase struct {
+		err       error
+		runAsUser bool
+		opts      Options
+	}
+	testCases := []testCase{{
+		// Run these tests only as a user
+		runAsUser: true,
+		opts:      Options{UserMode: true},
+		err:       nil,
+	}}
+	for _, tc := range testCases {
+		t.Run(fmt.Sprintf("as %s", userString), func(t *testing.T) {
+			if (userString == "root" || userString == "system") && tc.runAsUser {
+				t.Skip("skipping user test while running as superuser")
+			} else if (userString != "root" && userString != "system") && !tc.runAsUser {
+				t.Skip("skipping superuser test while running as user")
+			}
+			ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
+			defer cancel()
+			units, err := GetUnits(ctx, tc.opts)
+			if !errors.Is(err, tc.err) {
+				t.Errorf("error is %v, but should have been %v", err, tc.err)
+			}
+			if len(units) == 0 {
+				t.Errorf("Expected at least one unit, but got none")
+			}
+			unit := units[0]
+			if unit.Name == "" {
+				t.Errorf("Expected unit name to be non-empty, but got empty")
+			}
+			if unit.Load == "" {
+				t.Errorf("Expected unit load state to be non-empty, but got empty")
+			}
+			if unit.Active == "" {
+				t.Errorf("Expected unit active state to be non-empty, but got empty")
+			}
+			if unit.Sub == "" {
+				t.Errorf("Expected unit sub state to be non-empty, but got empty")
+			}
+			if unit.Description == "" {
+				t.Errorf("Expected unit description to be non-empty, but got empty")
+			}
+		})
+	}
+}
+
 func TestGetPID(t *testing.T) {
 	type testCase struct {
 		unit      string

structs.go

@@ -1,5 +1,15 @@
+//go:build linux
+
 package systemctl
 
 type Options struct {
 	UserMode bool
 }
+
+type Unit struct {
+	Name        string
+	Load        string
+	Active      string
+	Sub         string
+	Description string
+}

systemctl.go

@@ -1,3 +1,5 @@
+//go:build linux
+
 package systemctl
 
 import (

util.go

@@ -1,3 +1,5 @@
+//go:build linux
+
 package systemctl
 
 import (