[teleport-update] Remove warning when running Teleport on platforms without systemd (#51465)

* improve detection logic on non-systemd platforms

* adjust

* remove OS check

Author: sclevine

lib/autoupdate/agent/process.go

@@ -330,12 +330,28 @@ func (s SystemdService) IsPresent(ctx context.Context) (bool, error) {
 
 // checkSystem returns an error if the system is not compatible with this process manager.
 func (s SystemdService) checkSystem(ctx context.Context) error {
-	_, err := os.Stat("/run/systemd/system")
-	if errors.Is(err, os.ErrNotExist) {
+	present, err := hasSystemD()
+	if err != nil {
+		return trace.Wrap(err)
+	}
+	if !present {
 		s.Log.ErrorContext(ctx, "This system does not support systemd, which is required by the updater.")
 		return trace.Wrap(ErrNotSupported)
 	}
-	return trace.Wrap(err)
+	return nil
+
+}
+
+// hasSystemD returns true if the system uses the SystemD process manager.
+func hasSystemD() (bool, error) {
+	_, err := os.Stat("/run/systemd/system")
+	if errors.Is(err, os.ErrNotExist) {
+		return false, nil
+	}
+	if err != nil {
+		return false, trace.Wrap(err)
+	}
+	return true, nil
 }
 
 // systemctl returns a systemctl subcommand, converting the output to logs.

lib/autoupdate/agent/telemetry.go

@@ -31,6 +31,13 @@ import (
 // The binary is considered managed if it lives under /opt/teleport, but not within the package
 // path at /opt/teleport/system.
 func IsManagedByUpdater() (bool, error) {
+	systemd, err := hasSystemD()
+	if err != nil {
+		return false, trace.Wrap(err)
+	}
+	if !systemd {
+		return false, nil
+	}
 	teleportPath, err := os.Readlink("/proc/self/exe")
 	if err != nil {
 		return false, trace.Wrap(err, "cannot find Teleport binary")
@@ -52,6 +59,13 @@ func IsManagedByUpdater() (bool, error) {
 // and the default installation (with teleport.service as the unit file name).
 // The binary is considered managed and default if it lives within /opt/teleport/default.
 func IsManagedAndDefault() (bool, error) {
+	systemd, err := hasSystemD()
+	if err != nil {
+		return false, trace.Wrap(err)
+	}
+	if !systemd {
+		return false, nil
+	}
 	teleportPath, err := os.Readlink("/proc/self/exe")
 	if err != nil {
 		return false, trace.Wrap(err, "cannot find Teleport binary")