Better error when the server is unable to write in the backend (#8697)

cmd/fs-v1.go

@@ -20,10 +20,12 @@ import (
 	"bytes"
 	"context"
 	"errors"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"net/http"
 	"os"
+	"os/user"
 	"path"
 	"path/filepath"
 	"sort"
@@ -129,7 +131,15 @@ func NewFSObjectLayer(fsPath string) (ObjectLayer, error) {
 		if err == errMinDiskSize {
 			return nil, err
 		}
-		return nil, config.ErrUnableToWriteInBackend(err)
+		// Show a descriptive error with a hint about how to fix it.
+		var username string
+		if u, err := user.Current(); err == nil {
+			username = u.Username
+		} else {
+			username = "<your-username>"
+		}
+		hint := fmt.Sprintf("Use 'sudo chown %s %s && sudo chmod u+rxw %s' to provide sufficient permissions.", username, fsPath, fsPath)
+		return nil, config.ErrUnableToWriteInBackend(err).Hint(hint)
 	}
 
 	// Assign a new UUID for FS minio mode. Each server instance