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

cmd/config/errors-utils.go

@@ -36,6 +36,16 @@ type Err struct {
 	hint   string
 }
 
+// Clone returns a new Err struct with the same information
+func (u Err) Clone() Err {
+	return Err{
+		msg:    u.msg,
+		detail: u.detail,
+		action: u.action,
+		hint:   u.hint,
+	}
+}
+
 // Return the error message
 func (u Err) Error() string {
 	if u.detail == "" {
@@ -49,12 +59,16 @@ func (u Err) Error() string {
 
 // Msg - Replace the current error's message
 func (u Err) Msg(m string, args ...interface{}) Err {
-	return Err{
+	e := u.Clone()
-		msg:    fmt.Sprintf(m, args...),
+	e.msg = fmt.Sprintf(m, args...)
-		detail: u.detail,
+	return e
-		action: u.action,
-		hint:   u.hint,
 }
+
+// Hint - Replace the current error's message
+func (u Err) Hint(m string, args ...interface{}) Err {
+	e := u.Clone()
+	e.hint = fmt.Sprintf(m, args...)
+	return e
 }
 
 // ErrFn function wrapper

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

cmd/storage-rest-server.go

@@ -24,6 +24,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"os/user"
 	"path"
 	"strconv"
 	"strings"
@@ -608,7 +609,16 @@ func registerStorageRESTHandlers(router *mux.Router, endpointZones EndpointZones
 			}
 			storage, err := newPosix(endpoint.Path)
 			if err != nil {
-				logger.Fatal(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("Run the following command to add the convenient permissions: `sudo chown %s %s && sudo chmod u+rxw %s`",
+					username, endpoint.Path, endpoint.Path)
+				logger.Fatal(config.ErrUnableToWriteInBackend(err).Hint(hint),
 					"Unable to initialize posix backend")
 			}