I frequently eject an usb stick, and then realize I still need it.

If I unmount the drive in Disk Utility, I can just remount it, but if I eject, it's gone.

  • Not showed in Finder
  • Not showed in diskutil
  • Not showed in ls /dev
  • Is still showed in System Information under USB.

How can I mount the disk without unplugging and inserting it?

  • 1
    Had a similar question pop up here for Windows. A way to make that work was to disable the USB root hub the device was connected to and re-enable it, which then initialized the usb stick. A similar methodology may work for this issue, I just am not familiar with the OS in question to guide you through a similar process. – DHayes Feb 19 '10 at 14:00
  • @DHayes @Pepijn - indeed, there are a couple of q's on StackOverflow on the same issue, but they seem to be about Windows. stackoverflow.com/questions/916296/… .. stackoverflow.com/questions/138394/… – quack quixote Feb 19 '10 at 15:15
  • the reason the "disable/enable USB root hub" works is because initiating a USB slave device happens when the slave detects it's plugged in, not from the host side. but when you do it to the hub, it forces all the connected devices to disconnect/reconnect. now what you need is a way to identify the hub, disable it, then re-enable it. note this will reset all other devices on that hub. – quack quixote Feb 19 '10 at 15:20

You can remount an ejected hd using "hdiutil attach" and the appropriate /dev/ device (the BSD name under System Information). As you said, this does not work for flash drives (the /dev/ device will disappear).

kextunload IOUSBMassStorageClass.kext;
kextload /System/Library/Extensions/IOUSBMassStorageClass.kext

Will unmount and remount all USB storage devices...

  • Where do I find the BSD name under System Information? Do you mean system profiler? – AndyL Apr 15 '10 at 23:53
  • hints.macworld.com/article.php?story=20070712062603762 suggests system_profiler SPFireWireDataType | grep "BSD Name: disk.$" but I get no output at all from that -- system_profiler SPFireWireDataType just lists my FireWire speed, nothing else. Maybe the cable is faulty or something... – tripleee Oct 8 '14 at 16:33

Terminal Command was off by a little. The real command is:

diskutil mountDisk <<diskx>>*

where you replace <<diskx>> with the disk number you found using

diskutil list


diskutil mountDisk disk3

will mount the disk with the id of disk3

  • 2
    You can also specify the name of the disk like diskutil mountDisk "Western Digital". – Lri Jun 12 '12 at 4:23

If you are using a Mac, one solution is to simply put your computer to sleep and then wake it up again. It's a great solution if you're feeling lazy, but it will obviously be faster to just unplug and re-insert your drive.

  • 2
    Perfect. I was lazy, and as my laptop is 10 feet away from me, and unplugging would involve standing up, this would be my accepted solution! – maxwellb May 28 '13 at 6:01

I've had the same problem with external USB & Firewire drives; you eject them using 'disk utility' (perhaps by mistake) only to have to physically disconnect/reconnect the drive in order to get Mac OS X to see them again; despite them being visible under 'System Profiler'.

This is more than an inconvenience if using a daisy-chain of Firewire HDDs...

Here's what worked for me; try this from within Terminal. (1st make sure you have 'diskutil' installed - see note below.)

cmd line:

diskutil list

diskutil mountDisk /dev/diskx

where diskx correlates to the physical device reference as displayed under the "list" command e.g. disk2

NB: try MacPorts for http://www.macports.org/


I recently released an app exactly for this purpose called Mountain. Mountain can unmount external drives as well as remount them later.

  • 1
    It's great that you wrote an application that solves this issue, but it would be preferable if you would also explain how to use it to solve the issue. – Der Hochstapler Sep 26 '12 at 11:38
  • Hi Oliver, you can download a trial version of Mountain from appgineers.de/mountain It is nearly self explaining. Simply use Mountain to unmount your USB drive. Afterwards Mountain will allow you to remount the drive again. – Jan Linxweiler Oct 9 '12 at 15:26
  • I have no use for the application myself. I just wanted to remind you that we prefer answers that go into detail about solutions. Given that you wrote this application, you have every option to give it a proper presentation. You may want to have a look at meta.superuser.com/questions/5329/… – Der Hochstapler Oct 9 '12 at 15:36
  • Does it also shuts of USB fan automatically when the Mac goes to sleep? Please see (apple.stackexchange.com/questions/157826/…) @JanLinxweiler – alper Jul 20 '20 at 0:28

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