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force OS X to rescan for USB devices?

by Wooden Brain / October 10, 2009 8:42 AM PDT

Is there a way to do this? I've found that periodically certain USB devices, particularly those connected to a powered hub, are not recognized by OS X after a restart. They require being physically unplugged and replugged. This problem is much worse with Snow Leopard. 100% of the time an Apple USB Modem has this issue and frankly it's driving me a bit nuts.

Interestingly the USB Modem in question _is_ listed in System profiler. However it does not appear as a recognized modem in /dev/ and so it won't appear in modem software like dialers, caller id, etc.

so the question is, is there a terminal command one could issue to force a rescan of usb devices?

or any other likely solution to emulate unplugging and replugging them?

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Probably the hub, not OS X
by lkrupp / October 10, 2009 11:56 AM PDT

What brand of powered hub are you using? I had the exact same problem you describe using a D-Link 7 port UBS hub. I switched to a Belkin 7 port hub and the problem disappeared completely. It has not returned. I now have two Belkin hubs connected to my 24" iMac and no problems.

Bottom line I would bet your problem is caused by the hub you are using and not OS X

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It is a Belkin
by Wooden Brain / October 10, 2009 1:25 PM PDT

Hmm... well it is a Belkin USB 2.0 7 port hub. so....

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Basic troubleshooting
by lkrupp / October 11, 2009 2:04 AM PDT
In reply to: It is a Belkin

Well, there's nothing preventing the hub from being defective. You could try a swapping usb cables around to see if the trouble follows the cable or the device. You could try a different master cable from the hub to the usb port on the Mac. It would cost money but you could try a new usb hub. All I can say is that I'm running OS X 10.6.1 on a 24" iMac (July, 2008) with two of the Belkin hubs and don't have the issue. Bottom line is this should not be happening and I seriously doubt that it is cause by the operating system. I can also report that I don't see this issue popping up on other Mac sites I visit. That doesn't mean other people don't have the problem but it isn't very common apparently.

Good luck.

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modem works directly
by Wooden Brain / October 12, 2009 12:42 AM PDT
In reply to: Basic troubleshooting

When you say your USB hubs don't have this issue, are you talking specifically about a USB modem? Because other devices work -- it's just that one. And it works fine plugged directly into the MacPro. Trouble is of course that too many devices require direct connections (in my case, this modem, an iPhone, an LCD monitor) and thus there's no room in the back for a connection to the HUB, meaning i have to plug my iPhone into the front. I basically disagree that it's not OS X. After all the modem works after restart when unplugged and replugged. It seems to be a problem with OS X scanning the USB system after a restart then.

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I have a D-Link 7 port USB modem
by mrmacfixit Forum moderator / October 12, 2009 5:57 AM PDT
In reply to: modem works directly

and don't have this problem.
My iPhone plugs into the hub, as does my printer, TomTom, card reader and joystick.

Why is the LCD monitor plugged into the hub? Perhaps to provide extra ports on the monitor?

Just asking


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by Wooden Brain / October 12, 2009 6:54 AM PDT

The iPhone sometimes works through the hub but i found it didn't work well or reliably so it was recommended (in an Apple kbase article as I recall) to plug it in directly -- which i have done. The LCD monitor is plugged in directly also (not to the hub) and yes also to provide the monitor extra ports.

so right now what i have is:

-- iPhone (front plug)
-- LCD monitor (back plug)
-- keyboard
-- mouse
-- trackball
-- iMic (microphone)
-- USB Modem (back plug)
-- USB Hub (Belkin)
-- Scanner
-- Hard drive
-- card reader
-- other stuff occasionally used and plugged into hub

I'd like the hard drive plugged in directly (more reliable I think when dealing with data) but now the USB modem is hogging the only available back port.

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grr can't edit post
by Wooden Brain / October 12, 2009 7:00 AM PDT
In reply to: configuration

that didn't draw correctly and i didn't preview.

-- iPhone (front port)
-- LCD monitor (back port)
-- --> keyboard
-- -- -- --> mouse
-- --> trackball
-- --> iMic (microphone)
-- Apple USB Modem (back port)
-- Belkin USB Hub (back port)
-- --> Scanner
-- --> Hard drive
-- --> card reader
-- --> other stuff occasionally used and plugged into hub

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I do indeed have the Apple USB Modem
by lkrupp / October 12, 2009 10:33 AM PDT
In reply to: modem works directly

I have the Apple USB modem plugged into my Belkin hub. When rebooting it always appears and works as normal. When I had the D-Link hub the Apple USB Modem was one of the devices that would drop off the bus when booting. Another device that had the issue was my APC UPS (Back-UPS NS 1250). As you I had to physically unplug and plug in the devices to get them back. After switching to the Belkin hubs I longer experience any issues like yours. In my case, at least, it was definitely the bran of hub I was using. Either that or the D-Link hub was defective.

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not the hub
by dbennettks / October 12, 2009 8:14 AM PDT

I have this same problem with a macally laser mouse. Sometimes it starts with the system and works fine all day. Other times, it I restart the system, or shut down the system, the mouse never works again. Unplugging the mouse from either the MacBook Pro USB port, or from the keyboard's USB port and replugging it doesn't do a thing to bring it back to life.

And the next day, it works for who knows what reason...

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USB hub on Mac
by AbkJoi8970 / March 11, 2010 10:44 PM PST
In reply to: not the hub

I noticed the USB problem as well. I have a Macally USB keyboard connected to my old G4 Mini, running OSX 10.4.11, sometimes after a restart, I had to unplug and replug it to get it to work. Now I use the same keyboard on my new Mac mini OS X 10.5.6, the problem disappeared. However, the USB hub I had on the G4 mini works great, but I use the same hub on my new mini and after every restart, I have to unplug and replug the power cord to the hub to get it to work. Is this a Mac OS issue?

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