OS X Mountain Lion Developer Preview 3 Available for Dev Download

Apr 18, 2012 - 15 Comments

OS X Mountain Lion Developer Preview 3

Apple has released OS X Mountain Lion Developer Preview 3 to those registered with the Mac Developer program. The new build comes as 12A178q and includes many bug fixes, though it still includes a fairly lengthy list of known issues and bugs. This is the third beta release of OS X Mountain Lion, which currently has a rough public release date of “Summer” .

Developers can download OS X Mountain Lion DP3 from the App Store, though logging in through the developer center is necessary in order to receive a redemption code.

Due to stability issues and future upgrade problems, Mountain Lion Developer Preview should not be the primary operating system on a Mac. Follow a guide to set up a dual boot system between OS X 10.8 Beta and the more stable OS X 10.7 build for best results.


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Posted by: Paul Horowitz in Mac OS, News


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  1. Isidiros Sklivanos says:

    DP3 is a very fast and stable release i use it with no errors,bugs or anything else.I note that i am using final cut studio professionally.

  2. doctorfresh says:


    1. Insert start up disk (doesn’t matter which system)
    2. When available, select disk utilities from menu (at top)
    3. Restore from time machine backup (assuming you have one)

    Otherwise – you should have made a backup (reboot) disk (on USB flash drive or whatever) when you installed Lion

    Otherwise – you could restore your system to Snow Leopard (or whatever disk you have), then upgrade to Lion through the App Store, which will recall that you have bought it

    Takes a while but worth it to clear the rubbish off the hard drive anyway. I like a good clean install from time to time

    Re ML: I found that one of the settings in Mail was broken and it said that SSL was off (i.e. box unticked) when it was in fact on. So, I couldn’t use Mail in ML to get my works mail, which was a deal breaker for me (for now). I did like the Reminders App (and Notifications)

    Looking forward to the final or closer versions when the bug in Mail has been fixed.

  3. brah says:

    Hi, how do I reinstall lion over mt lion dev preview?

    Without having to do a erase of the entire disk : (

    Thanks! Lol this is my spare imac so it’s not end of world but rather avoid having to copy few hundred gigs of junk.

  4. Jeffrey A Barclay says:

    Overall – works fine, only issue I’m having is Safari crashes after 1-2 min. Here is part of the error log:

    Process: Safari [690]
    Path: /Applications/Safari.app/Contents/MacOS/Safari
    Identifier: com.apple.Safari
    Version: 5.2 (8536.6.1)
    Build Info: WebBrowser-7536006001000000~6
    Code Type: X86-64 (Native)
    Parent Process: launchd [153]
    User ID: 501

    Date/Time: 2012-04-23 08:34:13.649 -0400
    OS Version: Mac OS X 10.8 (12A178q)
    Report Version: 10

    Interval Since Last Report: 22518 sec
    Crashes Since Last Report: 8
    Per-App Interval Since Last Report: 210 sec
    Per-App Crashes Since Last Report: 7
    Anonymous UUID: F7FAA124-8958-46A0-9484-1B3414A1D241

    Crashed Thread: 0 Dispatch queue: NSPersistentUI Work

    Exception Type: EXC_BAD_ACCESS (SIGSEGV)
    Exception Codes: KERN_INVALID_ADDRESS at 0x0000000000000000

    VM Regions Near 0:
    __TEXT 0000000101a6f000-0000000101a70000 [ 4K] r-x/rwx SM=COW /Applications/Safari.app/Contents/MacOS/Safari

    Application Specific Information:
    Enabled Extensions:
    com.diigo.safari.awesomeScreenshot-5DXNM3K2CT (1.3.2 – 1.3.2) Awesome Screenshot
    com.jeremyhubert.livecsseditor-6ULL56D9UV (1.1 – 1.1) Live CSS Editor
    com.awarepixel.safari.bettersource-24E7DYSH92 (1.0 – 1.0) BetterSource
    com.sonereker.vss-6GDPUK989W (1 – 1.1) View Style Sheets
    com.personalwebdesign.googletoolbar-CW7MY6965B (9 – 1.9) GoogleToolBar

    objc[690]: garbage collection is OFF

    Thread 0 Crashed:: Dispatch queue: NSPersistentUI Work
    0 com.apple.CoreGraphics 0x00007fff841f4461 CGSShmemGuardLock + 14
    1 com.apple.CoreGraphics 0x00007fff841f37b4 _CGSLockWindow + 1154
    2 com.apple.CoreGraphics 0x00007fff8428f2c9 CGSLockWindowBackingStore + 234
    3 com.apple.CoreGraphics 0x00007fff8428ee50 __CGPixelAccessLockWindowAccess + 90
    4 com.apple.CoreGraphics 0x00007fff8428eddb CGPixelAccessLock + 46
    5 com.apple.AppKit 0x00007fff87a33258 -[NSPersistentUIManager snapshotWindow:handler:] + 202
    6 com.apple.AppKit 0x00007fff88231616 -[NSPersistentUIManager _updateSnapshotForWindowNumber:forWindowID:encryptionUUID:encryptionKey:encryptionKeyGeneration:waitUntilDone:] + 564
    7 com.apple.AppKit 0x00007fff8822e839 __85-[NSPersistentUIManager flushAllChangesOptionallyWaitingUntilDone:updatingSnapshots:]_block_invoke_0 + 1334
    8 libdispatch.dylib 0x00007fff878f8527 _dispatch_client_callout + 8
    9 libdispatch.dylib 0x00007fff878ebfb3 _dispatch_barrier_sync_f_invoke + 39
    10 com.apple.AppKit 0x00007fff87a326b0 -[NSPersistentUIManager flushAllChangesOptionallyWaitingUntilDone:updatingSnapshots:] + 675
    11 com.apple.AppKit 0x00007fff87a323d7 -[NSPersistentUIManager flushPersistentStateAndClose:waitingUntilDone:] + 180
    12 com.apple.AppKit 0x00007fff88230655 __42-[NSPersistentUIManager acquireDirtyState]_block_invoke_0 + 55
    13 libdispatch.dylib 0x00007fff878f8527 _dispatch_client_callout + 8
    14 libdispatch.dylib 0x00007fff878ead13 _dispatch_source_invoke + 691
    15 libdispatch.dylib 0x00007fff878ea7b7 _dispatch_queue_invoke + 72
    16 libdispatch.dylib 0x00007fff878edbc0 _dispatch_main_queue_callback_4CF + 220
    17 com.apple.CoreFoundation 0x00007fff8b0a5d9e __CFRunLoopRun + 1614
    18 com.apple.CoreFoundation 0x00007fff8b0a5352 CFRunLoopRunSpecific + 290
    19 com.apple.HIToolbox 0x00007fff87019d14 RunCurrentEventLoopInMode + 209
    20 com.apple.HIToolbox 0x00007fff8702155e ReceiveNextEventCommon + 356
    21 com.apple.HIToolbox 0x00007fff870213ef BlockUntilNextEventMatchingListInMode + 62
    22 com.apple.AppKit 0x00007fff879de39b _DPSNextEvent + 685
    23 com.apple.AppKit 0x00007fff879ddc59 -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 128
    24 com.apple.Safari.framework 0x00007fff86bafcaa -[BrowserApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 162
    25 com.apple.AppKit 0x00007fff879da283 -[NSApplication run] + 517
    26 com.apple.AppKit 0x00007fff87c498bb NSApplicationMain + 869
    27 com.apple.Safari.framework 0x00007fff86d6fb36 SafariMain + 166
    28 libdyld.dylib 0x00007fff84f557e1 start + 1

  5. Gaboriker says:

    Hy guys.
    I use the DP3 as my main system on a latest Mini.
    I use my computer for everyday use..
    The new DP works fine.. I dont met with crashes. I use Chrome on it, i dont like safari.

  6. kaps says:

    Is mirroring active on DP3

  7. Varadero says:

    Amazing! works perfectly! I am using DP3 as my main system and there are no issues; safari crashing was fixed, and imessage now works much better in terms of sync.

    • richardheath94 says:

      I am doing this also, but apparently we can’t upgrade from this to the retail version…. I’m thinking i will have to go back to lion??

  8. Mr. Hilarious says:

    beta version, wait for a better version

  9. adam says:

    I almost use only Mountain Lion from the DP1, It work nice, so better than lion or leopard when was in Development… It’s Natural, Leopard and Lion was have big OS Changes… Mountain Lion is what was Snow Leopard after Leopard, a big Clean Debug…

  10. Brett Lewis says:

    I have been used both build 1 and build 2 on my personal and work machines. Just updated to build 3 and everything works. Amazing that you get complainers about bugs in pre-release software. That is why they have it in beta.

    • Dave says:

      Can you tell me if it puts Ad-Hoc Networks back in and I might think about updating. That is all that will make it worthwhile. As I don’t care about bugs and I am on the dev program but not actually a dev.
      If you don’t know how go to the airport button and click create local network. (If its there)

  11. Dave says:

    To be honest neither of them were unstable for general every day use. I use my Mac running Developer Build 1 as the main operating system for about 10 hours a day and the only errors I ever got were with Safari bugging out occasionally and not being able to restart with Mail open. That was basically it apart from minor things.

  12. Tom says:

    DP1 and DP2 were basically unusable, hope this one is better.

  13. Release Notes says:

    Release Notes

    OS X Mountain Lion Developer Preview 3 is prerelease software. Do not use this prerelease software in a commercial operating environment or with important data. You should back up all of your data before installing this software and regularly back up data while using the software. You will not be able to upgrade from the OS X Mountain Lion Developer Preview to the final release.

    If an installation of OS X Developer Preview 3 fails, try using Disk Utility from a Recovery HD to repair the disk.

    Architecture Requirements
    The OS X Mountain Lion Developer Preview supports the following Macs:
    • iMac (Mid 2007 or later)
    • MacBook (13-inch Aluminum, Late 2008), (13-inch, Early 2009 or later)
    • MacBook Pro (13-inch, Mid-2009 or later), (15-inch, Mid/Late 2007 or later), (17-inch, Late 2007 or later)
    • MacBook Air (Late 2008 or later)
    • Mac Mini (Early 2009 or later)
    • Mac Pro (Early 2008 or later)

    Known Issues
    – On systems with FileVault enabled, canceling the restart to the Mountain Lion Developer Preview 3 Installer may leave your system unable to present a password dialog at boot time. You
    can repair the problem by holding down command-R to boot to the Recovery OS and then using Disk Utility to unlock and Repair your volume.
    – Installing OS X 10.8 over 10.7.2 or earlier with FileVault turned on may fail
    – Pre-Lion FileVault user accounts are not supported in this Developer Preview
    – Some Apple menu items such as Restart may not work when a sandboxed app is in the foreground
    – iTunes no longer syncs Notes
    – Mail’s photo browser cannot access the iPhoto library
    – Back to My Mac doesn’t work for the first 5 minutes after rebooting
    – DVD Player may not launch after inserting a DVD on some systems
    – Most help topics are unavailable in this Developer Preview
    – In the Recovery HD:
    – Some icons may be missing
    – Network Utility’s Lookup pane does not work
    – Time Machine restoration via a AFP share does not work
    – Restoring from a Time Machine backup via AFP does not work
    – Migration from a Time Machine backup that excludes paths such as /System may yield an unusable system
    – Brightness settings may change unexpectedly after reboot
    – Display brightness may be dim after sleep or reboot
    – If Mail is hidden at logout time, it may not be correctly relaunched during a subsequent login but will appear to be running
    – Java applets may not work in Safari
    – QuickTime screen recordings may produce corrupted videos or cause an exception when run on machines with NVDIA graphics
    Game Center
    – In this seed, the Game Center application will view Production data by default. Games in development will be programmatically switched to use the Sandbox server environment
    – No Top Games are displayed on the Me tab and no game recommendations are shown on the Games tab
    – To use Game Center in your game on OS X, you must install a provisioning profile that enables Game Center for your app. Code signing, entitlements, and provisioning profiles are all
    described in detail in Tools Workflow Guide for Mac
    – Multiplayer gaming with Game Center between iOS and OS X is not available in this seed
    – In the Game Center app, game detail information such as game provider, pricing, etc. is not displayed
    – The local peer-to-peer GameKit API (GKSession, GKPeerPickerController, and related classes) is not supported

    Bug Reporting
    This build is being provided to you for testing and development purposes. Should you encounter any problems, please submit a bug report using the online Bug Reporter at bugreporter.apple.com/>. Please make sure to include “10.8 (12A178q)” in the bug title and description. This information will ensure that your bug is processed quickly.

    When submitting a bug report, please make sure to include a Summary, Steps to Reproduce, Expected Results, Actual Results, and the diagnostic output generated by running ʻsudo sysdiagnoseʼ in the Terminal.

    For complete instructions on submitting bug reports, please visit the Bug Reporting page at .

    Thank you for your support.

    Apple World wide Developer Relations

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