I just downloaded Lion and am pretty eager to install it, but I can use every minute I have, so I'd rather not install it now if it means my system is unusable for 30+ minutes.

How long should I expect a Mac to be unusable during the upgrade process?

  • Could anyone explain the downvote? The question seems pretty relevant to me: there is little information to be found regarding the actual install process. Jul 20, 2011 at 13:44
  • 3
    I didn't down vote it, but it's a major system upgrade - you have to expect some downtime for maintenance.
    – Thomas
    Jul 20, 2011 at 13:51
  • 9
    feh. I downvote your downvote. There's a difference between a bad question and a naive question. Jul 20, 2011 at 13:56
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    I'm sure a lot of people are wondering how long it's going to take and how long their system will be unusable. Many OS upgrade processes allow the user to continue to use their system while they unpack and copy files, so the question is reasonable. I've rewritten the question a bit. Jul 20, 2011 at 14:00
  • 4
    My flippant answer was "Till you hear it roar!" but it actually just plays some lame music.
    – Ɱark Ƭ
    Jul 20, 2011 at 15:17

12 Answers 12


It's a safe bet that most people are out of business for less than an hour. Of course, you'll probably be spending hours exploring all the new features, so you might want to count that against your system being unusable for "real work" due to "exploration and play".

Since you can't easily interrupt things and won't have use of the mac once the installer logs you out to start the upgrade, do give yourself a little window in case things run long.

Here are some ballpark numbers people are reporting for upgrades with real life amounts of data on their macs:

  • iMac / Mac Pro + SSD: 8 to 15 minutes
  • iMac / Mac Pro + HD: 12 to 20 minutes
  • Portables: 15 to 30 minutes
  • full drives / Air with HD: 30 to 45 minutes

Furthermore, you won't really know how long it will take if problems crop up moving thousands of tiny files or the process hangs. Then you will need to research what to do if trying again doesn't sort things out for you.

Even if your install should take 15 minutes, why risk it until the pressure is off?

The problem with any prediction is that there are four parts to the install:

  1. common prep tasks (pre-download any updates - lion won't have many to pre download now since it's new)
  2. a file system check of all your data (to avoid problems with bad files or bad file system structure)
  3. the standard install (move the old, write the new - most macs capable of Lion will be within 50% of each other for this part)
  4. upgrade script to crawl through all the your files and programs, upgrade things, and then delete the now un-needed files.

Parts 2 and 4 are where "slow installs" take the majority of your time.

Most people will be done in less than an hour - but you can't really know if your install will go long until you let it start. It matters little that other people had a good experience if your is going to be especially slow.

You can run a full file system check before starting to be sure your directories won't trap the installer in an infinite loop, but other than deleting things like un-needed apps and files that might need "migration", you can't speed up the parts of the process that depend on your pre-existing data.

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    Thanks for the thorough answer, especially regarding the setup stages! Jul 20, 2011 at 14:22
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    Major upgrades touch files that may have lain dormant for years. Problems with unused code or incompatible extras come to light during an upgrade. It isn't meant to cause issues, just a "house of cards" is more likely to come down when you are re-plumbing the system.
    – bmike
    Jul 20, 2011 at 18:59

I just installed the upgrade and it took 45 minutes on a MacBook Pro mid 2010 spec. I have the 500 Gb drive partitioned equally mac and bootcamp.

The only problem I've found so far is that VMWare Fusion seems to have lost how it connects to my Bootcamp partition. I've verified that the Bootcamp partition is still there by booting into it.

  • I'm curious - how large a HD and how much free space. I have almost the same generation hardware :-). Thanks!
    – bmike
    Jul 20, 2011 at 17:50
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    500GB split into 2 equal partitions :)
    – John Mc
    Aug 4, 2011 at 17:45

After downloading it, the upgrade from Snow Leopard to Lion has taken 15-20 minutes on average and I literally have to do nothing to facilitate it. I grab a coffee and the upgrade's done before my cup's empty.

  • This was on a 27" iMac with stock RAM. The key metric here is after the download. The download takes forever but your system is totally usable while downloading. Jul 20, 2011 at 14:05

The installation on my MacBook Pro (early 2009) took exactly 21 minutes on a Crucial C300 SSD. It initially estimated 35 minutes. Add two 30 seconds reboots.


I'm running it on a sacrificial 2008 model iMac, 4Gb ram, 320Gb hard drive (with about 60Gb spare), 2.4 Ghz C2D processor. It reckons it's going to take about 35 minutes (and after 5 minutes is currently estimating about 30 minutes still).

I think you really are going to have to accept that your system will be unusable for a half hour or so while you upgrade.... and if you don't backup first, and there's a problem, it could be unusable for a lot longer than that!

I won't update my main work machine for a week or two yet, for this very reason.


On my 2010 iMac 21" it took about 90 minutes. In part this is because I have a lot of development tools on the system and it appears after having completed the upgrade that Lion rearranged and updated some of these tools (which is above and beyond the "typical" update).


It really depends on your system setup. I have installed it on 2 machines so far.

  • On a Macbook Pro i5 w/8gb of ram it took approx. 35 minutes
  • On a Macbook Pro C2D w/4gb of ram it took almost an hour.

It says 33 minutes at first reboot, but is taking more than 45. Mac book pro 4GB core 2 duo 2.4GHz


This will depend on your Mac's disk subsystem more than anything, then CPU speed, as well as whether or not you elected to create a DVD from which to install Lion.

My 2011 iMac (3.4GHz i7, 16GB RAM, SSD+HDD) took 11.5 minutes from hitting the "Install" button, to being booted into Lion.


Appears to have stalled at the "Install Mac OS X" screen

Shows "About 33 minutes" for the last 15 minutes, with no movement of the progress bar.

Hoping it'll kick in soon.

Mid 2010 MBP 17" w/ i7 4GB RAM approx 60GB free space on drive, 250GB drive.

And as I typed this... It actually changed to "About 32 minutes" so I'm breathing again.

As identified above, number of files appears to be key, I have millions of files on this machine.


20 minutes into process.

  • Hooray and welcome to the site. I hope the upgrade goes well.
    – bmike
    Jul 20, 2011 at 19:27

Just upgraded my MacBook Pro 13in with an i5 and a 320 GB HD. The download took about 25 minutes, and then about the same for the install process.

While it was downloading I was able to work normally, so it was only unavailable during the 25 minutes of the install process.

Free disk space actually increased (?! maybe it removed some old installer backup files); before I had 234 GB available, now df -h reports 239 GB available.

Another thing is that I had XCode 4 installed in Snow Leopard, and now it complained that it won't run on Lion. However, the new XCode is now free again in the App Store, so I downloaded it again and it runs fine now.


New OS installs can have problems. OSX is not imune (though I'm going the guess most people will have a lot less trouble than XP -> Vista).

There's no advantage in running Lion. Well, Mission Control looks nifty, and the security will be great, and support for file versions will be a life saver for the muggles who don't use Git (or even dropbox), and autosave will even save hardcore Git user's bacon.

There's a new Python installation. Will that replace my interpreter? I doubt it, but a new install can take hours to recover from.

Just play it safe. Or not. Find the bugs, and then alert me.

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