Detect systemd on mounter startup

pkg/util/mount/mount.go

@@ -94,15 +94,6 @@ func (mounter *SafeFormatAndMount) FormatAndMount(source string, target string,
 	return mounter.formatAndMount(source, target, fstype, options)
 }
 
-// New returns a mount.Interface for the current system.
-// It provides options to override the default mounter behavior.
-// mounterPath allows using an alternative to `/bin/mount` for mounting.
-func New(mounterPath string) Interface {
-	return &Mounter{
-		mounterPath: mounterPath,
-	}
-}
-
 // GetMountRefs finds all other references to the device referenced
 // by mountPath; returns a list of paths.
 func GetMountRefs(mounter Interface, mountPath string) ([]string, error) {

pkg/util/mount/mount_linux.go

@@ -55,6 +55,17 @@ const (
 // kubelet is running in the host's root mount namespace.
 type Mounter struct {
 	mounterPath string
+	withSystemd bool
+}
+
+// New returns a mount.Interface for the current system.
+// It provides options to override the default mounter behavior.
+// mounterPath allows using an alternative to `/bin/mount` for mounting.
+func New(mounterPath string) Interface {
+	return &Mounter{
+		mounterPath: mounterPath,
+		withSystemd: detectSystemd(),
+	}
 }
 
 // Mount mounts source to target as fstype with given options. 'source' and 'fstype' must
@@ -68,18 +79,18 @@ func (mounter *Mounter) Mount(source string, target string, fstype string, optio
 	mounterPath := ""
 	bind, bindRemountOpts := isBind(options)
 	if bind {
-		err := doMount(mounterPath, defaultMountCommand, source, target, fstype, []string{"bind"})
+		err := mounter.doMount(mounterPath, defaultMountCommand, source, target, fstype, []string{"bind"})
 		if err != nil {
 			return err
 		}
-		return doMount(mounterPath, defaultMountCommand, source, target, fstype, bindRemountOpts)
+		return mounter.doMount(mounterPath, defaultMountCommand, source, target, fstype, bindRemountOpts)
 	}
 	// The list of filesystems that require containerized mounter on GCI image cluster
 	fsTypesNeedMounter := sets.NewString("nfs", "glusterfs", "ceph", "cifs")
 	if fsTypesNeedMounter.Has(fstype) {
 		mounterPath = mounter.mounterPath
 	}
-	return doMount(mounterPath, defaultMountCommand, source, target, fstype, options)
+	return mounter.doMount(mounterPath, defaultMountCommand, source, target, fstype, options)
 }
 
 // isBind detects whether a bind mount is being requested and makes the remount options to
@@ -108,14 +119,14 @@ func isBind(options []string) (bool, []string) {
 }
 
 // doMount runs the mount command. mounterPath is the path to mounter binary if containerized mounter is used.
-func doMount(mounterPath string, mountCmd string, source string, target string, fstype string, options []string) error {
+func (m *Mounter) doMount(mounterPath string, mountCmd string, source string, target string, fstype string, options []string) error {
 	mountArgs := makeMountArgs(source, target, fstype, options)
 	if len(mounterPath) > 0 {
 		mountArgs = append([]string{mountCmd}, mountArgs...)
 		mountCmd = mounterPath
 	}
 
-	if systemdRunPath, err := exec.LookPath("systemd-run"); err == nil {
+	if m.withSystemd {
 		// Try to run mount via systemd-run --scope. This will escape the
 		// service where kubelet runs and any fuse daemons will be started in a
 		// specific scope. kubelet service than can be restarted without killing
@@ -138,7 +149,7 @@ func doMount(mounterPath string, mountCmd string, source string, target string,
 		//
 		// systemd-mount is not used because it's too new for older distros
 		// (CentOS 7, Debian Jessie).
-		mountCmd, mountArgs = addSystemdScope(systemdRunPath, target, mountCmd, mountArgs)
+		mountCmd, mountArgs = addSystemdScope("systemd-run", target, mountCmd, mountArgs)
 	} else {
 		// No systemd-run on the host (or we failed to check it), assume kubelet
 		// does not run as a systemd service.
@@ -157,6 +168,31 @@ func doMount(mounterPath string, mountCmd string, source string, target string,
 	return err
 }
 
+// detectSystemd returns true if OS runs with systemd as init. When not sure
+// (permission errors, ...), it returns false.
+// There may be different ways how to detect systemd, this one makes sure that
+// systemd-runs (needed by Mount()) works.
+func detectSystemd() bool {
+	if _, err := exec.LookPath("systemd-run"); err != nil {
+		glog.V(2).Infof("Detected OS without systemd")
+		return false
+	}
+	// Try to run systemd-run --scope /bin/true, that should be enough
+	// to make sure that systemd is really running and not just installed,
+	// which happens when running in a container with a systemd-based image
+	// but with different pid 1.
+	cmd := exec.Command("systemd-run", "--description=Kubernetes systemd probe", "--scope", "true")
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		glog.V(2).Infof("Cannot run systemd-run, assuming non-systemd OS")
+		glog.V(4).Infof("systemd-run failed with: %v", err)
+		glog.V(4).Infof("systemd-run output: %s", string(output))
+		return false
+	}
+	glog.V(2).Infof("Detected OS with systemd")
+	return true
+}
+
 // makeMountArgs makes the arguments to the mount(8) command.
 func makeMountArgs(source, target, fstype string, options []string) []string {
 	// Build mount command as follows:

pkg/util/mount/mount_unsupported.go

@@ -22,6 +22,15 @@ type Mounter struct {
 	mounterPath string
 }
 
+// New returns a mount.Interface for the current system.
+// It provides options to override the default mounter behavior.
+// mounterPath allows using an alternative to `/bin/mount` for mounting.
+func New(mounterPath string) Interface {
+	return &Mounter{
+		mounterPath: mounterPath,
+	}
+}
+
 func (mounter *Mounter) Mount(source string, target string, fstype string, options []string) error {
 	return nil
 }