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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?

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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
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2 Answers

up vote 3 down vote accepted

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...

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Where do I find the BSD name under System Information? Do you mean system profiler? – AndyL Apr 15 '10 at 23:53
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up vote 1 down vote

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 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/

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