guests/linux: more verbose output when shared folder mount fails

[GH-4403]

CHANGELOG.md

@@ -53,6 +53,8 @@ BUG FIXES:
   - guests/fedora: Fix networks on Fedora 20 with libvirt. [GH-4104]
   - guests/freebsd: Rsync install for rsync synced folders work on
       FreeBSD 10. [GH-4008]
+  - guests/linux: Show more verbose error when shared folder mount fails.
+      [GH-4403]
   - guests/redhat: NFS setup should use systemd for RH7+ [GH-4228]
   - guests/smartos: Use `pfexec` for rsync. [GH-4274]
   - guests/windows: Reboot after hostname change. [GH-3987]

plugins/guests/linux/cap/mount_virtualbox_shared_folder.rb

@@ -41,10 +41,15 @@ module VagrantPlugins
           while true
             success = true
 
+            stderr = ""
             mount_commands.each do |command|
               no_such_device = false
+              stderr = ""
               status = machine.communicate.sudo(command, error_check: false) do |type, data|
-                no_such_device = true if type == :stderr && data =~ /No such device/i
+                if type == :stderr
+                  no_such_device = true if data =~ /No such device/i
+                  stderr += data.to_s
+                end
               end
 
               success = status == 0 && !no_such_device
@@ -56,7 +61,8 @@ module VagrantPlugins
             attempts += 1
             if attempts > 10
               raise Vagrant::Errors::LinuxMountFailed,
-                command: mount_commands.join("\n")
+                command: mount_commands.join("\n"),
+                output: stderr
             end
 
             sleep 2

templates/locales/en.yml

@@ -750,6 +750,10 @@ en:
         can work properly. The command attempted was:
 
         %{command}
+
+        The error output from the last command was:
+
+        %{output}
       linux_nfs_mount_failed: |-
         Mounting NFS shared folders failed. This is most often caused by the NFS
         client software not being installed on the guest machine. Please verify