Q: imax slow after install el capitan

When you see a beachball cursor or the slowness is especially bad, note the exact time: hour, minute, second.  

These instructions must be carried out as an administrator. If you have only one user account, you are the administrator.

Launch the Console application in any one of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad and start typing the name.

The title of the Console window should be All Messages. If it isn't, select

          SYSTEM LOG QUERIES ▹ All Messages

from the log list on the left. If you don't see that list, select

          View ▹ Show Log List

from the menu bar at the top of the screen.

Each message in the log begins with the date and time when it was entered. Scroll back to the time you noted above.

Select the messages entered from then until the end of the episode, or until they start to repeat, whichever comes first.

Copy the messages to the Clipboard by pressing the key combination command-C. Paste into a reply to this message by pressing command-V.

The log contains a vast amount of information, almost all of it useless for solving any particular problem. When posting a log extract, be selective. A few dozen lines are almost always more than enough.

Please don't indiscriminately dump thousands of lines from the log into this discussion.

Please don't post screenshots of log messages—post the text.

Some private information, such as your name, may appear in the log. Anonymize before posting.

When you post the log extract, you might see an error message on the web page: "You have included content in your post that is not permitted," or "The message contains invalid characters." That's a bug in the forum software. Please post the text on Pastebin, then post a link here to the page you created.

If you have an account on Pastebin, please don't select Private from the Paste Exposure menu on the page, because then no one but you will be able to see it.

It takes an hour to boot up.  Then all the login programs need to update, another 30 mins.  Then there's a beachball lag of 10 minutes after every keystroke or mouse event.

I just want to get a few tax files I neglected to back up.  Target mode doesn't work.  It comes up looking normal and then nothing, after waiting 2 hrs.

You mentioned another way to get files off an unusable iMac?

disconnect all external devices except mouse and keyboard then reboot into safe mode

boot into safe mode

Try safe mode if your Mac doesn't finish starting up - Apple Support

then reboot, if the problem persists

check your hard drive integrity

Using Disk Utility to verify or repair disks - Apple Support

then reboot, if the problem persists

turn off file vault encryption

OS X Yosemite: Turn off FileVault encryption

in addition to these steps it may be necessary to uninstall any and all Mac Anti-Virus you may have on that computer. they have been documented as to being the root cause of OS X performance issues. Also uninstall any 3rd party utility such as Mac Keeper, Clean My Mac, Little Snitch, etc as these packages have been reported to cause serious performance issues with Mac OS

Thanks, then it might be Avast or a poorly uninstalled Mac keeper,

I started in safe mode no difference, I ran disk utility and HD looks fine, I've never used the FileVault encryption

Now how will I ever be able to uninstall Avast or Mac keeper remnants with the OS in this condition??

Isn't there a way other than Target Mode to get a few files off this iMac?

Avast is garbage ware on the mac, it causes far more damage than any other service it purports to offer.

https://www.avast.com/faq.php?article=AVKB67

Mac Keeper is scam ware, you should remove it with prejudice.

DO NOT follow the directions on their page, use this article:

http://www.macworld.com/article/2861435/software-utilities/how-to-uninstall-mack eeper-from-your-mac.html

Target mode see this article

Share files between two computers with target disk mode - Apple Support

I even tried target mode after the OS booted up using system preferences, but it says there was an error and I never got past that