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I have an external audio interface (M-audio fast track c400). In order to get my macbook to recognize it (display in audio/midi setup), I have to reboot, which is a hassle. I have had other m-audio interfaces that were automatically detected when connected, and I'm pretty sure this one should be the same. Most posts around the internet suggest updating the OS or the software/firmware for the device. I have done all of those with no luck. I am currently running OS X 10.8.5.

Is there a way to force OS X to reload the device? Preferably some command line voodoo that I could fire off quickly when needed or wrap up in a nice little shell script.

Edit: Progress..

The problem appears to be fixed now... I'm not sure how the following solved the problem. If you know, please comment!

Inspired by @sbugert's answer, I started looking into other system daemon's that might do the trick if restarted. As a shot in the dark I killed coreservicesd. This caused the OS to become visibly unstable and I was eventually logged out automatically. To my surprise, when I logged back in, my audio interface was recognized..

Based on that, I hypothesized that killing coreservicesd and logging out/in may be a possible (ugly) workaround. So I unplugged the interface and plugged it back in, and as expected, it was not recognized. So I killed coreservicesd and attempted to log out, however I could not get the system to log out due to the instability caused by killing coreservicesd. I eventually was forced to do a "hard" shutdown (i.e. holding the power button until it turns off). After booting up the macbook again, the interface is now recognized automatically every time I plug it in. I suspect that this "hard" reset may have solved the issue without all the shenanigans with the coreservices daemon, but I have no way to test that.

If anyone can shed light on this, please do!

Edit: It stopped working again so I don't know what's up.

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up vote 32 down vote accepted

This is what you need,

sudo kextunload /System/Library/Extensions/AppleHDA.kext
sudo kextload /System/Library/Extensions/AppleHDA.kext

But if you want to kill your coreaudio as well,

 ps aux | grep 'coreaudio[d]' | awk '{print $2}' | xargs sudo kill

use with caution.
The grep target is written this way specifically to exclude grepping the grep process itself in the ps out.

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The driver loading/unloading is the only thing that worked to make the Mac detect my headphones. THANK YOU! – wizonesolutions May 17 '14 at 0:26
The kext changes caused my laptop to reset - I don't recommend it. The fix for me was to go to Settings > Sound and check the Output is set correctly. – vaughan Dec 4 '14 at 17:58
@vaughan what is your OSX version? any special hardware? like fancy microphone or speakers or audio devices with specially drivers? – Ali Dec 4 '14 at 21:35
This temporarily brings back my sound. In my case, I have had audio issues ever since using a Plantronics USB headset that was provided to test Cisco Jabber. Reloading the AppleHDA kext provides temporary sound but video still lags and stutters. – Aaron Jan 22 '15 at 23:54
Works. I had to kill coreaudio first, probably because a track was playing - should've stopped it first. MacBook Pro 13, late 2013, 10.10.1 – VladFr Feb 5 '15 at 14:22

Try typing this into Terminal:

sudo killall coreaudiod

This will kill the coreaudio process and restart it.

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This is exactly what I was hoping for! ...but it doesn't seem to work. Upon executing the command I see all the internal audio devices disappear and reappear in Audio/MIDI setup, but the external interface does not appear with them. I also tried killall -KILL and killall -ABRT which have the same result. Perhaps something similar but lower-level needs to be done, like restarting/reloading all usb devices? – RyanM Sep 19 '13 at 19:34
This fixed my no sound effects problem. – wisbucky Mar 2 at 8:31
wow my issue was the internal speakers would stop working intermittently until i rebooted. thanks! this did the trick! – Elon Zito Apr 29 at 3:36

Same solution but with different variation

sudo kill -9 `ps ax|grep 'coreaudio[a-z]' | awk '{print $1}'`
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Don't use kill -9 just for the sake of it. A bare kill is perfectly sufficient to halt the daemon in normal circumstances. Indiscriminate use of -9 can lead to situations where a daemon shuts down so brutally that you can no longer restart it. – dland Dec 19 '14 at 9:15

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