containerd/containerd · error

ErrNoShmMount

ErrNoShmMount

Error message

no /dev/shm mount specified

What it means

ErrNoShmMount is returned by opts like WithDevShmSize/WithDevShm when the generated Spec has no mount at /dev/shm for them to configure. These opts mutate the existing shm mount entry; without one there is nothing to act on.

Source

Thrown at pkg/oci/spec_opts.go:1565

		if err != nil {
			return err
		}
		defer f.Close()

		sc := bufio.NewScanner(f)
		for sc.Scan() {
			vars = append(vars, sc.Text())
		}
		if err = sc.Err(); err != nil {
			return err
		}
		return WithEnv(vars)(nil, nil, nil, s)
	}
}

// ErrNoShmMount is returned when there is no /dev/shm mount specified in the config
// and an Opts was trying to set a configuration value on the mount.
var ErrNoShmMount = errors.New("no /dev/shm mount specified")

// WithDevShmSize sets the size of the /dev/shm mount for the container.
//
// The size value is specified in kb, kilobytes.
func WithDevShmSize(kb int64) SpecOpts {
	return func(ctx context.Context, _ Client, _ *containers.Container, s *Spec) error {
		for i, m := range s.Mounts {
			if filepath.Clean(m.Destination) == "/dev/shm" && m.Source == "shm" && m.Type == "tmpfs" {
				for i := 0; i < len(m.Options); i++ {
					if strings.HasPrefix(m.Options[i], "size=") {
						m.Options = append(m.Options[:i], m.Options[i+1:]...)
						i--
					}
				}
				s.Mounts[i].Options = append(m.Options, fmt.Sprintf("size=%dk", kb))
				return nil
			}
		}

View on GitHub (pinned to 4246446a2b)

Solutions

1. Add the shm mount before sizing it, e.g. ensure Spec.Mounts includes {Type: "shm", Source: "shm", Destination: "/dev/shm"}.
2. Use oci.WithDevShm (which adds the mount) before/instead of only WithDevShmSize.
3. Match with errors.Is(err, oci.ErrNoShmMount) and skip shm configuration for specs that legitimately have none.

Example fix

// before
opts := []oci.SpecOpts{oci.WithDevShmSize(65536)}
// after
opts := []oci.SpecOpts{oci.WithDevShm(65536)} // adds + sizes the /dev/shm mount

hasShm := false
for _, m := range spec.Mounts {
    if filepath.Clean(m.Destination) == "/dev/shm" { hasShm = true }
}
if !hasShm { /* add shm mount before applying WithDevShmSize */ }

if err := oci.WithDevShmSize(65536)(ctx, client, &ctr, &spec); err != nil {
    if errors.Is(err, oci.ErrNoShmMount) { /* add mount or skip */ }
}

When it happens

Trigger: Calling oci.WithDevShmSize(kb) (or WithDevShm) as a SpecOpt when the Spec's Mounts slice contains no mount whose destination is /dev/shm.

Common situations: Custom Spec built by hand without the default /dev/shm mount; opts applied in the wrong order so no shm mount was added yet; running on configs derived from non-Linux templates.

Related errors

• failed to activate mounts: %w
• no arguments specified
• spec does not contain Linux or Windows section
• rootfs absolute path is required
• ErrNoUsersFound

AI-assisted analysis of containerd/containerd@4246446a2b (2026-09-02). Data as JSON: /api/errors/6ca8e308fa07e93e. Report an issue: GitHub.