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I am currently running on macOS Sierra 10.12.6, and I want to upgrade it to the new macOS Catalina.

  • If I upgrade the OS without backing it up will I lose data??

  • And is it necessary to back up?

  • What will happen if I upgrade to macOS Catalina without backing up?

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  • 1
    Ideally, nothing will get lost. But what if something unexpected happens? As they say, Así es la vida. Follow Tetsujin’s advice in his answer.
    – Allan
    May 5, 2020 at 17:08
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    You should generally think about backups. What if your laptop breaks or get stolen? Time Machine is builtin to MacOS and requires a USB-disk or a suitably configured network drive. Use a password! If your machine is wiped or you get a new machine, it is very easy to reestablish your old environment from that.
    – Thorbjørn Ravn Andersen
    May 6, 2020 at 13:22
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    Yes, you can. I lost data upgrading from Mojave to Catalina: I had local data in /home/(username)/ (with modified /etc/auto_master and /etc/auto_home) and it was totally lost. Presumably the installer copied over Catalina /etc with original auto_* files which then hid my data. Fortunately (most of) it was backed up.
    – user7761803
    May 6, 2020 at 14:01
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    It should be noted that any 32-bit applications that you may have on your current system, will not work on Catalina. You won't "lose the applications", the files will remain, but they won't work.
    – Will Hartung
    May 6, 2020 at 21:15
  • I would start by checking whether you actually can upgrade to Catalina. You are running Sierra, which means you have a rather old hardware – make sure Catalina supports it. Otherwise the whole question is irrelevant.
    – Aleks G
    May 7, 2020 at 14:12

6 Answers 6

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61

Normally, nothing untoward will happen.

However, nothing is 100% certain, ever.

Backups are a necessary part of life. You really, really should always have at least one, preferably two; one being off-site.

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  • 8
    This can’t be upvoted enough.
    – Allan
    May 5, 2020 at 17:10
  • You will notice that @Tetsujin will probably break all records with such a simple and righteous answer. There is no such thing as failproof computing environment.
    – dan
    May 6, 2020 at 13:36
  • Apple's "Time Machine" feature makes backups very simple and automatic; I highly recommend hooking up an external drive and enabling Time Machine.
    – Jeremy Friesner
    May 6, 2020 at 15:16
  • It only takes losing it once. "Been there, done that", as they say. If the data matters, it should be backed up. Preferably in more than once place.
    – Marc Wilson
    May 6, 2020 at 16:39
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    Off-site storage was already mentioned.
    – Tetsujin
    May 7, 2020 at 6:03
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There's one scenario in which the answer is a definitive "yes" : obsolete applications.

As Apple is removing support for 32-bit entirely, you may find you have some specialized application which is no longer maintained, meaning there is no 64-bit binary available. If in addition you have data files in a format proprietary to that application, then once the application is unable to run, you have no way to access the data files.

I could say some nasty things about obsoleted proprietary data formats (Microsoft Office, I'm staring straight at YOU), but you get the idea here.

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    Very valid point, that's probably something anybody should check before upgrading to Catalina.
    – nohillside ♦
    May 6, 2020 at 12:13
  • Was just about to write a similarly worded answer; indeed I'd day that the Catalina upgrade has a high potential for (albeit a very specific kind of) data loss. Although one perhaps should rather call this "content loss".
    – Asmus
    May 6, 2020 at 12:39
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    I downvoted this answer because it's factually incorrect: Microsoft's OOXML file formats are non-proprietary and are open standards with freely accessible technical documentation and haven't been proprietary since Office 2007 - that's 13 years ago. Whereas Apple's iWork formats are very, very proprietary with no public documentation for them. Please don't post one-sided answers.
    – Dai
    May 6, 2020 at 13:59
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    @Dai You are factually incorrect -- Some of us don't consider 15 years to be a "long time" to archive data. Try opening Office files from 1998. Format obsoletion is one of the biggest headaches archivists deal with every day. The fundamental point of this answer has nothing to do with microsoft vs. apple vs oracle vs whoever anyway
    – Carl Witthoft
    May 6, 2020 at 14:52
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    Yeah you can still open office files from 1998 on modern versions of office programs. Been there - done that, recently! The 97-2004 formats are still valid for current versions of Microsoft Office.
    – HomoTechsual
    May 6, 2020 at 23:01
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What will happen if I upgrade to macOS Catalina without backing up?

If they don't get accidentally deleted during the update, you'll have to wait for them to get accidentally deleted some other time.

is it necessary to back up?

Only if you want to keep your files.

Apple introduced Time Machine with OS X Leopard in 2007. It could not be easier. Plug in a drive, turn on TM, and off you go. There is no reason not to have a backup, and I find it increasingly difficult to feel sorrow for anyone who loses files because they didn't have one.

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  • Comments are not for extended discussion; this conversation has been moved to chat.
    – nohillside ♦
    May 6, 2020 at 14:47
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Complementing other answers:

Apart from the system specific answers given by others (some losses may "just happen", 32 bit applications will no longer function) sudden unpredictable data loss is a fact of life in all computing systems. A "proper" backup plan is an essential part of all but the most trivial systems.

ALL hard drives fail (whether rotating rust or some form of solid state).
Time to loss typically varies between 1 decade and 1 hour after first use. (I've seen a PC with hard disk failure of a name brand drive within hours of 1st operation.)

Backups are such an essential part of life that data loss of a primary record should be no more than an inconvenience. If any data has more than near-zero value to you it should be backed up in a manner that makes loss nearly impossible. The value of "nearly" should approach certainty as the value increases.

I know or know of people who have lost whole theses due to a complete lack of backup.
Or priceless memories such as photos.
Just do it.

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  • Thank you! No one has a copy of your files and photos. Do the backups, please people.
    – bmike ♦
    May 7, 2020 at 3:27
  • @bmike Except for Homeland Security, obvs.
    – benwiggy
    May 7, 2020 at 9:56
  • Ha. @benwiggy I suppose - No one will give your files back when you ask nicely... it usually costs dearly if you don’t self backup. Basically, it’s their backup if they performed it and retained it.
    – bmike ♦
    May 7, 2020 at 11:30
  • The most attentive govt department: "NSA - you talk, we listen".
    – Russell McMahon
    May 7, 2020 at 12:54
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if normally updated it will not lose any data but if you want to clean install which is Good because latest os uses AFPS partition then you should backup which is a best practice.

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First: start making backups! You will need the backup one day.

Yes, you can lose data. No, the upgrade is designed by Apple to be as careful as possible in a normal situation. By normal I here mean that you save your data and documents in the normal places, that is under /home in your user folders or in folders you have created yourself directly under /.

If you have data in the "OS" folders, say under /etc or /bin and so on, don´t expect that data to survive an update. The update process will do its best, some files will be copied to a special folder, but some files may be replaced and your data lost.

And as other answers mention, your applications may not survive a new OS version. You might need to upgrade the applications as well in order to read the data. And there might not be newer versions available or they may come at a cost.

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