Installing ElCapitan from a TMbackup

zoran

macrumors 68040
Original poster
Jun 30, 2005
3,321
48
I have Sierra on an external drive (No1) that I use to boot with. On a different ext drive (No2) I have a TimeMachine backup from an ElCapitan system. I wish to delete Sierra from the ext drive (No1) and install Capitan as it is on the TMachine backup on the other external drive I have (No2).
How do I do this?
 

vertical smile

macrumors 601
Sep 23, 2014
4,593
5,702
I don't think you can.

You can restore your data from TM, but I don't think you can restore the OS. It is the probably the worse thing about TM.

Just a tip for the future, before you go to update to a new OS, clone the old one. I have a few external HDDs that is partitioned to fit a bunch of boot drives on it. Before upgrading, or to make an occasional back up, I just use CCC to clone to one of the drives.

I also use the drives to store bootable installers of the MacOS versions. It is really easy, although it involves using the Terminal app, but still really, really easy.

But, back to your problem, I am not sure if you can make a bootable installer if you are using a newer OS. I think you can make a current OS installer, and newer OS installers, but not older.
Anyone else know?

Do you have any access to Macs with older MacOS?
 

zoran

macrumors 68040
Original poster
Jun 30, 2005
3,321
48
Wait a sec, cant i boot using the ElCapitan TMbackup drive and from there to restore everything its on it? Of course i will erase the Sierra OS and everything on it so the ElCapitan will take its place!
 

vertical smile

macrumors 601
Sep 23, 2014
4,593
5,702
Wait a sec, cant i boot using the ElCapitan TMbackup drive and from there to restore everything its on it?
I am pretty sure that you cannot. Please, anyone correct me if I am wrong, but Time Machine is not a bootable source, it can only be used to restore or migrate data to another drive that has an OS on it.

This is why I kind of hate TM. I use it, but only for the purposes of quickly restoring something I deleted a while back. Something that has never actually happened.

I would also use it to migrate my data in the scenario of my boot drive crashing, and I didn't have a recent back up. This has happened before when I had a bad Fusion drive in my iMac.

I much rather deal with bootable cloned back ups though. They make much more sense to me than TM for most situations.

So, back to your problem, do you have access to an old bootable drive, or a Mac with an older OS on it?
[doublepost=1537884296][/doublepost]
I am pretty sure that you cannot. Please, anyone correct me if I am wrong
Maybe I am wrong.... I found this:

https://support.apple.com/kb/ph25593?locale=en_US

I am not sure if these means install an older OS or not, but it sounds like maybe you can.
[doublepost=1537884446][/doublepost]Actually, that sounds like that it takes you back to an early version of Sierra. So, maybe that won't work....

Anyone else have any insight on this issue?
 

treekram

macrumors 68000
Nov 9, 2015
1,849
404
Honolulu HI
Booting from an El Capitan (or any macOS version) TM backup is hit-or-miss, in my experience. Supposedly if you have an encrypted TM backup, it's less likely to work, but I am able to boot from my encrypted El Capitan TM backup. I don't know if there's circumstances peculiar to my situation (the TM disk was originally created in Mountain Lion) that makes it work but there are posters who say their non-encrypted El Capitan TM disk doesn't boot.

If you can't boot from the El Capitan TM disk, probably the easiest way to restore is to create a El Capitan USB installer, boot from it, and from it's Utilities menu, restore from the El Capitan TM disk.

If you don't have the El Capitan installer app, look at (step #4):
https://support.apple.com/en-us/HT206886

You can create a USB installer using the following:
https://support.apple.com/en-us/HT201372
 

Weaselboy

Moderator
Staff member
Jan 23, 2005
30,324
10,074
California
I wish to delete Sierra from the ext drive (No1) and install Capitan as it is on the TMachine backup on the other external drive I have (No2).
You can option key boot to a TM backup and get a restore screen. From there you use Disk Util to erase the drive then restore and the OS and all will be put back.

Problem is Apple broke this in El Capitan so it won't work. It worked both before and after El Capitan.

Someone here on the forum figured out how to make it work with El Capitan by editing a plist file on the TM disk, but I cannot recall how to do it.
 
  • Like
Reactions: zoran

jbarley

macrumors 68040
Jul 1, 2006
3,867
1,712
Vancouver Island
I am pretty sure that you cannot. Please, anyone correct me if I am wrong, but Time Machine is not a bootable source, it can only be used to restore or migrate data to another drive that has an OS on it.
You are correct in that Time Machine is not a bootable source, but it is accessible from the Recovery Hard disk menu, and it does restore a complete functional bootable system, you even get to pick the date that you wish to restore from.
[doublepost=1537915293][/doublepost]
You can option key boot to a TM backup and get a restore screen. From there you use Disk Util to erase the drive then restore and the OS and all will be put back.

Problem is Apple broke this in El Capitan so it won't work. It worked both before and after El Capitan.

Someone here on the forum figured out how to make it work with El Capitan by editing a plist file on the TM disk, but I cannot recall how to do it.
Funny I'd never noticed that I could not boot to the Time Machine drive in El-Cap, but that was because I've always accessed the Time Machine restore feature from the Recovery Hard disk menu, which still works nicely.
I just ran a restore before posting this to make sure.:D
 
  • Like
Reactions: Weaselboy
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.