MacOS 10.12 Sierra, 10.13 High Sierra, 10.14 Mojave audio completely stops working

I've noticed this for a while and it has driven me nuts! Out of nowhere, audio will completely stop working system wide, and until now the only fix I could find was to reboot. It happened on multiple MacBook Pro devices, of multiple generations, and continued across the last few versions of MacOS.

Now, though, it's easily fixable. In terminal, just issue the following command and audio should be back momentarily (if you're having the same issue as me):

In terminal, issue:       sudo killall coreaudiod

Enter your password and hit enter

That should do it!

macOS 10.12 Sierra - Corrupted MAC on input && No matching host key type

If you frequently SSH into network management devices, such as routers and switches, you may notice that in macOS 10.12, it doesn't work anymore.

There are two error message you'll need to fix:
- Unable to negotiate with X.X.X.X port 22: no matching host key type found. Their offer: ssh-dss
- Corrupted MAC on input. Connection to X.X.X.X closed by remote host.

Both errors are fixed by modifying the SSH config file. The fix follows:

In terminal, issue:       sudo nano /etc/ssh/ssh_config

Enter your password and hit enter

1. Scroll down until you see this line: 

         #   MACs hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-ripemd160

2.  Delete the pound sign, which will un-comment that line and make it active.

3. Now scroll down to the bottom of the document and add this line:  
        HostkeyAlgorithms ssh-dss

4. Hold Control and hit X to exit, hit Y to save, and Enter to apply. 

That should do it!

macOS 10.12 Sierra - Flush DNS

On macOS 10.12 Sierra, flushing DNS uses the same commands as 10.11 and previous.

To flush your DNS on macOS 10.12 Sierra, issue this command in terminal:

sudo dscacheutil -flushcache;sudo killall -HUP mDNSResponder;say flushed 

At the prompt, enter your password and hit the enter key. When it's done flushing your DNS, it will say so.  

Always run Windows command prompt as administrator

If I'm using command prompt on a Windows machine, there is a 99% chance that whatever I'm using it for needs to be run as administrator. Which frustrates me, since I need to right click the program each time and run it specially as an administrator. So instead, here's how to fix that on a 2012r2 machine. It will still prompt for UAC, unless you shut UAC off completely, but I would never do that.

Search for cmd, right click it, and click "Open file location"


Mine already took me to the shortcut version. So, right click it, click Properties, click the Shortcut tab, click Advanced in the lower right, and then check the box "Run as administrator". Click Ok, Apply. Now just toss that shortcut wherever you want, and it'll always run as administrator when you use it. I right click mine and put it in the taskbar, for quick access.



If yours doesn't take you to a shortcut version, it might take you right to the actual file in C:\Windows\system32. In that case, right click the file, and click Create Shortcut. It will prompt you to put the shortcut on your desktop. Click yes. When you find the shortcut on your desktop, simply follow the steps from above.

OS X 10.11 - Corrupted MAC on input.

If you frequently SSH into network management devices, such as routers and switches, you may notice that in 10.11, it doesn't work anymore. The error message received is: Corrupted MAC on input. ssh_packet_read: message authentication code incorrect.

To get around this, you just need to edit your ssh_config. I'll use nano in this example. 

In terminal, issue:       sudo nano /etc/ssh/ssh_config

Enter your password and hit enter

Scroll down until you see this line: 

#   MACs hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-ripemd160

Delete the pound sign, which will un-comment that line and make it active.

Hold Control and hit X to exit, hit Y to save, and Enter to apply. 

That should do it!

OS X 10.11 El Capitan - Flush DNS

On OS X 10.11 El Capitan, flushing DNS uses the same commands as 10.9 and previous. If you've seen the news, the last 10.10.4 betas showed that Apple has removed discoveryd and discoveryutil.


To flush your DNS on OS X 10.11, issue this command in terminal:

sudo dscacheutil -flushcache;sudo killall -HUP mDNSResponder;say flushed 

OS X 10.10.4 Yosemite - Flush DNS

I didn't realize this until now, but it looks like with Apple's removal of 'discoveryd' in the newest beta, 'discoveryutil' is also gone from the command line. To flush the DNS cache, we now need to revert back to the commands from 10.9 Mavericks.

I only noticed when clearing my cache suddenly resulted in "discoveryutil: command not found" errors when running "sudo discoveryutil mdnsflushcache". Looks like it's not my system acting up, since it carries across reboot.

For reference, the current command to use in the new 10.10.4 betas, and presumably moving forward, is:

sudo dscacheutil -flushcache;sudo killall -HUP mDNSResponder;say flushed