diff --git a/cmd/dups/main.go b/cmd/dups/main.go
new file mode 100644
index 0000000..7a6ca05
--- /dev/null
+++ b/cmd/dups/main.go
@@ -0,0 +1,169 @@
+package main
+
+import (
+	"crypto/rand"
+	"crypto/sha1"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"runtime"
+	"sync"
+	"time"
+)
+
+var (
+	flLoadMap  = flag.String("l", "", "load existing map from file")
+	flSaveMap  = flag.String("s", "hash-map.json", "file to save map of file hashes to")
+	flHardlink = flag.Bool("H", false, "hardlink the duplicate files")
+	flQuiet    = flag.Bool("q", false, "less output")
+	nprocs     = 1
+)
+
+func init() {
+	nprocs = runtime.NumCPU()
+	runtime.GOMAXPROCS(nprocs)
+}
+
+func main() {
+	flag.Parse()
+	for _, arg := range flag.Args() {
+		savings := int64(0)
+		found := map[string]string{}
+		if len(*flLoadMap) > 0 {
+			fh, err := os.Open(*flLoadMap)
+			if err != nil {
+				fmt.Fprintln(os.Stderr, err)
+				os.Exit(1)
+			}
+			buf, err := ioutil.ReadAll(fh)
+			if err != nil {
+				fmt.Fprintln(os.Stderr, err)
+				os.Exit(1)
+			}
+			if err = json.Unmarshal(buf, &found); err != nil {
+				fmt.Fprintln(os.Stderr, err)
+				os.Exit(1)
+			}
+		}
+		workers := make(chan int, nprocs)
+		mu := sync.Mutex{}
+		err := filepath.Walk(arg, func(path string, info os.FileInfo, err error) error {
+			/*
+				if err != nil {
+					return err
+				}
+			*/
+			if !info.Mode().IsRegular() {
+				return nil
+			}
+			workers <- 1
+			go func() {
+				defer func() { <-workers }()
+
+				fh, err := os.Open(path)
+				if err != nil {
+					fmt.Fprintln(os.Stderr, err, path)
+					return
+				}
+				defer fh.Close()
+
+				h := sha1.New()
+				if _, err = io.Copy(h, fh); err != nil {
+					fmt.Fprintln(os.Stderr, err, path)
+					return
+				}
+				sum := fmt.Sprintf("%x", h.Sum(nil))
+
+				// get the absolute filename
+				p, err := filepath.Abs(path)
+				if err != nil {
+					fmt.Fprintln(os.Stderr, err, path)
+					return
+				}
+				path = p
+
+				mu.Lock()
+				defer mu.Unlock()
+				if fpath, ok := found[sum]; ok && fpath != path {
+					if !(*flQuiet) {
+						fmt.Printf("%q is the same content as %q\n", path, fpath)
+					}
+					if *flHardlink {
+						if err = SafeLink(fpath, path); err != nil {
+							fmt.Fprintln(os.Stderr, err, path)
+							return
+						}
+						fmt.Printf("linked %q to %q\n", path, fpath)
+					}
+					savings += info.Size()
+				} else {
+					found[sum] = path
+				}
+			}()
+			return nil
+		})
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		}
+		for len(workers) > 0 {
+			time.Sleep(5 * time.Microsecond)
+		}
+		fmt.Printf("Savings of %fmb\n", float64(savings)/1024.0/1024.0)
+		fh, err := os.Create(*flSaveMap)
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		}
+		buf, err := json.Marshal(found)
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		}
+		_, err = fh.Write(buf)
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		}
+		fh.Close()
+		fmt.Fprintf(os.Stderr, "wrote %q\n", fh.Name())
+	}
+}
+
+// SafeLink overrides newname if it already exists. If there is an error in creating the link, the transaction is rolled back
+func SafeLink(oldname, newname string) error {
+	var backupName string
+	// check if newname exists
+	if fi, err := os.Stat(newname); err == nil && fi != nil {
+		// make a random name
+		buf := make([]byte, 5)
+		if _, err = rand.Read(buf); err != nil {
+			return err
+		}
+		backupName = fmt.Sprintf("%s.%x", newname, buf)
+		// move newname to the random name backupName
+		if err = os.Rename(newname, backupName); err != nil {
+			return err
+		}
+	}
+	// hardlink oldname to newname
+	if err := os.Link(oldname, newname); err != nil {
+		// if that failed, and there is a backupName
+		if len(backupName) > 0 {
+			// then move back the backup
+			if err = os.Rename(backupName, newname); err != nil {
+				return err
+			}
+		}
+		return err
+	}
+	// remove the backupName
+	if len(backupName) > 0 {
+		os.Remove(backupName)
+	}
+	return nil
+}