14 March 2015

Sudden appearance of mach_kernel

Yesterday, after permitting some recommended autoupdates to be installed on my Mac, two new items appeared on the menu of my hard disk.  One was a folder for "incompatible software" (empty, and dated 6 months ago, but never present at this level of my hierarchical menu).  I think this has appeared before after updates when the system replaces old components, but it's usually deeper down in the files.

Of more concern to me was a mysterious "mach_kernel" apparently dating from mid-December and described as a "Unix Executable file" - a scary virus-suggesting term.  I quickly did a Google search and found this:

The comment comes from a trustworthy Apple Support Community webpage.  I did type the requested command into terminal and received the favorable response of (?another) mach_kernel being in its proper place.  I'm tempted to delete this new one, but reluctant to do so.  I may have to defer blogging for a while until I get the details of this worked out.

FWIW, I've also found that I cannot now change the names of any of the folders in the image at the top without receiving a notice that "Finder wants to make changes" and then I have to type in my password.  That has never happened before, and it doesn't seem to be happening with other folders located deeper in the hierarchy.

Have any readers encountered this problem and dealt with it successfully?

Addendum:  I have also found this more recent advice:

- but I don't know whether to follow that advice since Terminal tells me I already have a mach_kernet elsewhere on the computer.  If I "hide" this new one, will it conflict with the other one?


  1. You don't say what version of the OS you are running. The mach_kernel file used to exist at the root and then either was moved to it's current location (/System/Library/Kernels/kernel) or simply made invisible.

    Try 'uname -a' from the Terminal:

    Darwin argent.local 14.1.0 Darwin Kernel Version 14.1.0: Thu Feb 26 19:26:47 PST 2015; root:xnu-2782.10.73~1/RELEASE_X86_64 x86_64 i386 MacBookPro9,2 Darwin

    See it matches your expectations.

    Also 'ls -l /System/Library/Kernels/'

    -rwxr-xr-x 1 root wheel 10618072 Feb 26 19:29 kernel

    1. I'm running OSX 10.9.5

      The "uname" command in Terminal generates a response that mentions "Darwin Kernel Version 13.4.0 with a date from December of 2014 and some "root" and "Release" numbers.

      The second query generates "no such file or directory."

      So, does that mean my mach_kernel was moved out of the system library up to "the top" where I can see it, and that I should "move it back" as that Apple Feb 2015 note suggests?

    2. I would leave it where it is. I don't recall the disposition of that file in 10.9.x. It looks like it is where it it should be. The command above — sudo chflags hidden /mach_kernel — will remove it from view.

      That Tech Note likely applies to systems running the Yosemite version so you might find yourself in a predicament if you were to delete or move it.

      The fact you used '"Unix Executable file" - a scary virus-suggesting term' makes me wary of any more technical suggestions. It is a UNIX computer, so there are lots of files matching that description doing lots of useful and necessary things inside that sleek case.

    3. I guess I should clarify that I was an English major and now I'm a retired old man. Computer technical information needs to be presented to me in an ELI5 manner.

  2. Oh, and the requests for a password when you muck about at the root of your system are to protect from inadvertent changes. It's been my experience that people sometimes want to "tidy things up" on their system and the result is that things get moved that shouldn't. I advise such thrillseekers to take apart and re-assemble a wristwatch as a better use of their energy.

  3. I suppose you are familiar with the adage, "If it ain't broke, don't fix it"?
    Quit fiddlin' with it.

    1. Ed, I don't understand what you mean by "if it ain't broke..."

      Not being able to rename folders in my Finder would suggest to me that something is "broken."

    2. I didn't see where you couldn't rename folders. You mentioned that you could but were asked to authenticate first. That's not the same as "can't."

    3. You're quite correct that I shouldn't have said "can't" without the clarification. But that is the first time in my 25+ years of using Macs that I have been asked to authenticate before renaming a folder in the Finder, and a total change from several days ago.

    4. Not to worry, I was an English major too.

  4. my post vanished will try again. open disk utility and select the the top of the hierarchy showing your disk label on the left. Look at bottom of window to see that it says the S.M.A.R.T status is "verified". If it show you something else in red, immediately back up the disk and purchase a replacement!!! On the right, select the first-aid tab, then click "repair disk" this will take a very long time to run, go for a walk outside. When you may see it repaired something. Next on the left hand hierarchy list, select one down the hierarchy to the disks label (its freindly name). go back to first aid, and select "repair permissions". This is fairly fast. It's a good idea to do this housekeeping a couple times a year.

    1. Thank you, charlie. That makes sense.

      My S.M.A.R.T. status is verified (and I backed up my hard disk yesterday). A long walk sounds like a good idea.

    2. A permissions sweep (verify/repair permissions) is a fine suggestion, embarrassed I didn't think of it.

    3. A belated thank you, charlie, for the detailed directions on repairing permissions. I had to wait until I had finished my taxes, then backed up my computer and followed your suggestions. The process went smoothly (I discover in the process that I have 182,000 folders and 816,000 files !) - but the mach kernel is still in that new place.

      I've decided to leave it alone, since the system is working fine otherwise. My next step will be to upgrade from 10.9.5 to 10.10, but I'm waiting for an iteration beyond 10.10.3 since I see quite a few complaints about the early versions (tho my wife has installed it without problems).

  5. Now as for the mach kernel being out in public. Don't worry the fact that its not hiding is probably because of your messed up permissions (see post above). Don't delete it because you are running system 10.9 and its needed for that. ( If you had been running 10.10 ( it has been moved to a new location and given a new name) then it would be safe to delete this legacy file.) You can just follow the advice above for hiding it... But I strongly advise you to repair the permissions as I described first.
    Another way to give your a computer a tune up is to upgrade it to 10.10. This will give your whole system a once over and will almost certainly fix everything including the permissions. That assumes your computer is new enough to upgrade to 10.10.

  6. disk utility is located in /Applications/Utilities/

  7. http://en.wikipedia.org/wiki/Mach_%28kernel%29

  8. Do NOT DELETE THIS. this is the same file you checked to see if it exists-- it is not a duplicate. I also notice that a lot of hidden files are visible in your finder view.
    It is therefore likely that this problem is not due to the individual file settings of hidden/not hidden but to a general setting in the finder to show the hidden files.
    There are some settings that tell the finder to obey the hidden file preferences and it is possible these have been borked on your computer and it is now showing you all the hidden files (e.g. System ). Another possibility is that this situation only applies to the specific finder window you have open. Try opening another finder window and see if the problem persists. Likewise reboot and see. If not then you had a temproary situation where the finder preferences were messed up.

    If this persists across reboots then got to this page:
    it tells you how to access the secret finder preferences that control if a file is hidden. Don't do this lightly as messing with defaults can quickly get you in over your head. That said the ones on this page are relatively safe as long as you don't make any typos.
    You may possibly need to be the root user to get those commands to execute in the terminal. to become the root user in a terminal type the following:
    sudo -s
    and it will ask you for your admin password.
    I also see some signs of bad housekeeping on your part: it is not a good idea to put your own folders in the top level directory of the disk. move things like "to do" lists into your user directory. this is also useful for migrating to a new computer.

  9. I will echo that what Charlie says above is the correct way to fix this minor issue. Do NOT follow any instructions that say to delete or move the file.

    In unix, the "kernel" is the core of the operating system. The Mach Kernel is the type of Unix that Mac OS is based on. It's history can be read here: http://en.wikipedia.org/wiki/Mach_%28kernel%29

    All you are seeing here are the underpinnings of the OS X operating system being revealed. There is no need to panic about it. Think of it as being akin to seeing all the back stages and support tunnels behind Disney World. As a friend in the computing industry once stated, "Unix is like an Easter egg hunt. There are still many surprises hidden in there and you never quite know what you will find next."

  10. Gees, I sure am glad I have an Asus computer running Windows Vista. Whatever its shortcomings and despite its age of 6 years, I never have these sorts of problems :-)


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