What causes "failed to create the temp dir" in owasp-amass/amass?

Pre-create the output directory with correct permissions (os.MkdirAll(outdir, 0o755)) before session creation

failed to create the temp dir

Error message

failed to create the temp dir

What it means

After the output directory resolves, createTemporaryDir calls os.MkdirTemp(outdir, "session-"+id) to create the per-session directory; if that syscall fails, this error replaces the detailed OS error. It indicates the output directory exists as a path value but a temp directory could not be created inside it.

Source

Thrown at engine/sessions/session.go:280

	}
	// Initialize the database store
	store, err := assetdb.New(s.dbtype, s.dsn)
	if err != nil {
		return errors.New("failed to initialize database store: " + err.Error())
	}
	s.db = store
	return nil
}

func (s *Session) createTemporaryDir() (string, error) {
	outdir := config.OutputDirectory()
	if outdir == "" {
		return "", errors.New("failed to obtain the output directory")
	}

	dir, err := os.MkdirTemp(outdir, "session-"+s.ID().String())
	if err != nil {
		return "", errors.New("failed to create the temp dir")
	}

	return dir, nil
}

func (s *Session) createSessionPipelines(reg et.Registry) error {
	s.pipelines = make(et.SessionPipelines, len(oam.AssetList))

	for _, atype := range oam.AssetList {
		p, err := reg.BuildAssetPipeline(s.Ctx(), atype)
		if err != nil {
			return err
		}
		s.pipelines[atype] = p
	}

	return nil
}

View on GitHub (pinned to 79299dce87)

Solutions

Pre-create the output directory with correct permissions (os.MkdirAll(outdir, 0o755)) before session creation
Check directory ownership/writability for the user running the process
Confirm the output path is a directory, not a file, and on a writable (not read-only) filesystem
Check disk space and inode availability on the volume
Temporarily log the underlying os.MkdirTemp error to see the precise errno

Example fix

// before
outdir := config.OutputDirectory()
if _, err := os.Stat(outdir); err != nil { log.Fatal(err) }
// after
outdir := config.OutputDirectory()
if err := os.MkdirAll(outdir, 0o755); err != nil {
    log.Fatalf("cannot create output dir %s: %v", outdir, err)
}

Defensive patterns

Strategy: validation

Validate before calling

outdir := config.OutputDirectory()
if err := os.MkdirAll(outdir, 0o755); err != nil {
    return fmt.Errorf("cannot prepare output dir %s: %w", outdir, err)
}
if fi, err := os.Stat(outdir); err != nil || !fi.IsDir() || unix.Access(outdir, unix.W_OK) != nil {
    return fmt.Errorf("output dir %s is not writable", outdir)
}

Try / catch

if err := session.CreateSession(cfg); err != nil {
    if strings.Contains(err.Error(), "failed to create the temp dir") {
        log.Fatalf("cannot create temp dir under %s: check permissions, disk space, and mount flags", config.OutputDirectory())
    }
    return err
}

Prevention

Create the output directory at service startup with os.MkdirAll and correct ownership
Run the process as a user with write access to the output path
Monitor disk space on the volume holding the output directory
Avoid read-only container mounts on the output path

When it happens

Trigger: CreateSession -> createTemporaryDir when os.MkdirTemp fails: the output directory does not exist, is not writable, is actually a file, or the filesystem is full/read-only.

Common situations: Output directory configured but never created (app does not MkdirAll); permission denied after service user change; disk full on the volume; SELinux/container read-only mount on the output path; session ID producing an unusable prefix.

Understand the failure class

Background: mkdir permission denied (EACCES): failed to create directory errors explained — this error's family across 32 libraries.

Related errors

AI-assisted analysis of owasp-amass/amass@79299dce87 (2026-09-06). Data as JSON: /api/errors/db32abfde883c150. Report an issue: GitHub.