Fix Catalina Beta boot cache problem (Little Snitch related)

If your app need to modify boot caches on macos, like Little Snitch, it may fail on macos Catalina beta version after macos updated from Software Update due to system bug.


Some app, like Little Snitch, need to update boot caches while installing. But due to bug introduced by Software Update of Catalina beta, it may fail. After reboot, you will get an error like “version mismatched” reported by Little Snitch.


To fix that, you need to boot into the recovery mode (CMD+R while booting), unlock your hard disk if you enabled FileVault, start Terminal from menu and enter:

touch /Volumes/<Volume>/System/Library/Extensions

and press enter. <Volume> is your hard disk volume. You can use ls /Volumes to check all mounted volumes.

This command will finish very fast. After it run, wait about 10 seconds and restart your computer. This will fix the boot cache problem.



Use both iPhone and iPad on Keynote Presentation

I know some Apple iOS device users. When they need to do a presentation provided by Keynote, they know how to connect the projector to an iOS device by a Lightning Digital AV Adapter or a Lighting to VGA Adapter. Some advanced users even know they can connect the projector to their Mac computers and use an iOS device to do a remote controlling for Keynote presentation, if they have them both.

But they ain’t good enough. If you do it on an iOS device, you have to get close to the projector. The cable for that connection is really heavy and uncomfortable if you want to hold your device with your show. Using a Mac computer is better, but I really hate to bring such a heavy metal just for using Keynote. Yes, I have a Macbook Pro, not a Macbook Air lol.

Today, I realize it’s possible to use Keynote Remote technology from one iOS device to make a show on another iOS device. If you like me, having both iPhone and iPad, there is a better solution.

To prepare, you need to make a connection between both Keynote apps.

  1. If you want to do this by WiFi, connect your iPhone and iPad to the same WiFi network. If you prefer Bluetooth, enable Bluetooth on both devices and turn off WiFi on one device to avoid WiFi interference.
  2. Open Keynote on iPad.
  3. On iPad, in the presentation manager, press the Keynote Remote button (the second one on the title bar, next to the + button) and tap Continue.
  4. Open Keynote on iPhone.
  5. On iPhone, open a presentation, press the button with a wrench icon, select Presentation Tools – Allow Remote Control, then turn on Enable Remotes. Tap Link next to the device of your iPhone. If you see other than 1 connection, make sure the connection is set correctly as in step 1.
  6. Four digits will be displayed on both device.
  7. Press Confirm on one device to finish this step.

To make a show:

  1. Open presentation on your iPhone and connect it to the projector.
  2. Open Keynote on your iPad and press the Keynote Remote button to start.
  3. Give it a little time for syncing data from your iPhone if you don’t want to do that blindly.

Now you can hold your iPad and leave your iPhone next to the projector. I prefer to use iPad for controlling for a dual slides display. If you want to do it reversely, swap all jobs on iPad and iPhone.

Next time, when Apple TV is not provided by your client, you may want to try this. One more piece of advice: do not forget to get your iPhone back after your show.

Reset LaunchPad in OSX Yosemite

In OSX Yosemite, the way for resetting LaunchPad has been changed.

New command is:
defaults write ResetLaunchPad -bool true; killall Dock

Warning: By resetting LaunchPad, all settings related to LaunchPad will be removed like position of icons and groups.

Solved: Handoff problem with iOS 8 and OSX 10.10

As a developer, I’ve tested OSX 10.10 (Yosemite) and iOS 8 for a long time. There was a strange issue after I reset my OSX:

When I try to make a call from OSX, the calling box will be closed after 10 sec without any information in OSX 10.10 DP4. In DP5, it will say that “Your iPhone is not configu…”. Also, no SMS can be sent from OSX either. But when typing message on iOS, there will be an icon displayed on the left side of Dock in OSX.

Finally, I know the reason.

We know that the account name is one email address. And you can add more email addresses as alias. The problem of the current version of iOS 8 and OSX 10.10 is: if you used the email address for Facetime and iMessage is different from the one used in iCloud for OSX, no matter these email addresses are linked to the same iCloud account or not, the handoff function won’t work, just like the situation I mentioned above.

Before Apple fix this bug, we have to use the same email address for these place.

This issue is submitted to Apple.

Disable Safe Sleep in OSX

While OSX falling asleep, it save all memory into a local disk file, for avoiding data loss caused by batteries running out while sleeping. But it comes with some disadvantages:

  • That file is the same size as your memory. It eats your hard drive. You may not want this on a SSD solution;
  • Writing a so huge file requires more time while entering sleep mode.

And, when is the last time your mac’s battery running out while sleeping? Never, I guess.

Good news is, if you pleased, you can disable this function by running these two commands in terminal window.

sudo rm /private/var/vm/sleepimage
sudo pmset -a hibernatemode 0

These commands above will delete the existed image file and disable the further creation process of this file. Of course, after taking these steps, your computer will not able to resume from sleep while battery running out, by taking a cold boot instead. You may lost all unsaved data in that rare situation.

Time Sync between OSX and Windows

Through Boot Camp, we can install a dedicated Windows instance with OSX in the same mac computer. Due to the different time models, you may see that the time is not right while booting into another system.


  • OSX, as well as other unix-like system, setting UTC to hardware time, convert to local time dynamically while displaying;
  • Windows use LOCAL TIME as hardware time directly.

You may not realized this because one of these reasons below:

  • You are in England, or other countries in Time Zone 0 (GMT);
  • Your computer system, both OSX and Windows has a client of NTP, which will get the right time from internet server very soon after booting. Certainly, the related computer should have an active internet connection.

How to fix it:

I didn’t find a way to change the time model of OSX. But we can do that in Windows.

  1. Start Regedit;
  2. Nav to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation;
  3. Create a new DWORD named as RealTimeIsUniversal, and set it value to 1.