Clean install of El Capitan possible?

[macstatic]

I'm leaning towards upgrading to 10.11 El Capitan (from 10.9.5 Mavericks) in order to get IOS 13 support with iTunes.
(I've created a multi-partition SSD with 10.11 El Capitan, 10.12 Sierra and 10.13 High Sierra on my Mac Pro and with a little playing around they don't seem to differ much on my mid-2010 Mac Pro (24GB RAM, SSD for OSX/apps, HDDs for file storage and backups) but from what I've read El Capitan is the best option above 10.9.5 for performance with older Macs).

But for that test-partition I had to go through a LOT of hassle and problems. I finally succeeded, but had to install 10.6 Snow Leopard on the newly partitioned drive, go through all the updates (ending up with 10.6.8 and all the other Snow Leopard updates). From then on I ran the 10.11 El Capitan installer (from a USB stick using Diskmaker X), and keeping in mind to adjust the clock in the Terminal so as to be within its valid certificate date. Finally adding all the El Capitan updates.

Is this the only way to go?

 

[CoastalOR]

According to Apple's instructions the minimum OS for installing El Capitan is Snow Leopard.

How to download and install macOS – Apple Support (UK)

Download and install current or previous versions of the Mac operating system on compatible Mac computers.

support.apple.com

The requirement for Snow Leopard may be to allow the download El Capitan, but it may not be necessary if you have already created a El Capitan USB installer and you are doing a clean install. If you need to install over a existing macOS install or need to migrate data than that is different and the minimum of Snow Leopard would be needed.

I would recommend trying to install El Capitan from the USB installer without changing the date in Terminal. The recent 24 Oct. 2019 certificate expiration did not effect my El Capitan USB installer, it did effect Sierra, High Sierra, and Mojave USB installers.

 

[macstatic]

According to Apple's instructions the minimum OS for installing El Capitan is Snow Leopard.

How to download and install macOS – Apple Support (UK)

Download and install current or previous versions of the Mac operating system on compatible Mac computers.

support.apple.com

The requirement for Snow Leopard may be to allow the download El Capitan, but it may not be necessary if you have already created a El Capitan USB installer and you are doing a clean install. If you need to install over a existing macOS install or need to migrate data than that is different and the minimum of Snow Leopard would be needed.

I must have done something wrong at some stage because I absolutely could not install it on an empty partition. I'm pretty sure I chose the usual "journaled" format.
After installing Snow Leopard and upgrading to 10.6.8 I was finally allowed by the installer to proceed with the installation.

I used the same link as you quoted above, for downloading 10.11 El Capitan, but strangely that presented me with a DMG file (disk image as far as I know), and when double clicked I ended up with a .pkg file as the installer. Diskmaker X wouldn't accept this and after some web research I've understood that the installer should be an application.
After some further web research I actually was able to download an application type 10.11 installer, but frustratingly I can't remember where I got it from. I'm pretty sure it was a link to somewhere on Apple's site(s) as I'm very cautious about installing an OS that could been tampered with.

UPDATE: I think the 10.11 application installer might have been downloaded from the App Store using this iTunes link (which I found in this forum posting). It goes to an Appstore page which I haven't been able to find using its search function, so essentially hidden from most users.
So I just tried downloading it again (from within 10.9.5 Mavericks) but first received an error alert saying "We could not complete your purchase: this version of OSX 10.11 can not be installed on this computer". When pressing on the "More info" button I was sent to OSX Mavericks system requirements which is rather odd since I'm already on Mavericks.
I assume I need to install 10.6 Snow Leopard, update to 10.6.8 and try the same link there in order to get it (the 10.11 installer app, not the 10.11 installer DMG which can't (in my experience at least) be used with Diskmaker X to make a bootable USB installer).

I would recommend trying to install El Capitan from the USB installer without changing the date in Terminal. The recent 24 Oct. 2019 certificate expiration did not effect my El Capitan USB installer, it did effect Sierra, High Sierra, and Mojave USB installers.

Very strange. It all appeared well to begin with, but after a while I got an error message, so I remembered the date trick which allowed me to go through with the whole installation.
May I ask which 10.11 installation file you used, and how you got Diskmaker X to accept it if it in fact was the DMG file from the above download link?

I did read something about Apple resigning their installers so they could work for some more years (without doing the date "hack"), but I must have used that application type El Capitan installer (since I succeeded in making a USB installer with Diskmaker X) and that installer might not have had its signing updated.

 

[macstatic]

OK, I think I've got it! ?
First of all, the DMG file installer for 10.11 El Capitan (from the "How to upgrade to 10.11 El Capitan" Apple page) which I couldn't get to work with Diskmaker X isn't really a 10.11 installer app (like the ones you download from the Mac app store), but rather an installer for the 10.11 installer app!

Let me explain in case other are also wondering:

1) download OSX 10.11 from Apple (you'll end up with a DMG (disk image) file)
2) double-click the DMG disk image file (a window showing a PKG file will open up)
3) double-click the .PKG file (this starts an installer)
4) when the installer is done you'll find a 10.11 installer app (in your /Applications/ folder unless you told the installer to place it somewhere else)
5) Now you can either double-click the 10.11 installer app to upgrade your existing OSX version or use it with Diskmaker X to create a USB-bootable installer

From what I understand, the 10.11 DMG from the above link has had its certificates updated, so there's no need to do the Terminal date trick prior to installing 10.11 (unlike the 10.11 installer app downloadable from the Mac App store) which AFAIK needs to have this done.

I have now succeeded in making a USB installer from the downloaded DMG file but have yet to try and see if I can install OSX 10.11 on a blank partition/drive (I went through the whole procedure of installing OSX 10.6 Snow Leopard and upgrading to 10.6.8 first). I hope these last parts are unnecessary as it's quite time consuming while testing out things (which I'm doing now, selecting between different OSes for app compatibility/performance testing).

UPDATE:
Success! Using the DMG download of OSX 10.11 El Capitan (see above) and making a bootable USB-installer with Diskmaker X I finally managed to install 10.11 without installing 10.6.8 Snow Leopard first!
I don't know if I was refused to do this before because I had either tried to install it on a partition on a drive or because I named the partition prior to installing 10.11.
This time (since I was done testing and comparing between 10.11 El Capitan, 10.12 Sierra and 10.13 High Sierra) I erased the entire SSD first (using Disk Utility within 10.9.5 Mavericks) and didn't change the name either in Disk Utility nor in the Mavericks Finder afterwards. Any ideas if this would make a difference?

The installation worked without a hitch, and I didn't need to change the clock's date either. Strange, but very welcoming after all the previous hassles!

10.11 Seems not too different from 10.9 so far (I haven't used it extensively, mostly using the Finder and re-installing software) though it'll take a while to get used to the "flat" look which IMHO is quite ugly compared to 10.9 and earlier, but that's "progress" I guess, as they say.

 

[MacCandy]

Can you help me? I'm upgrading my mac pro 2,1 from OSX Lion to El Capitan using the pikify download. Trouble is, before being able to run the pikify script, the El Capitan installer must be unpacked in the Applications folder. I downloaded the .dmg from Apple and ran it. I have the El Capitan.pkg installed on a different drive...not the main MacIntosh HD drive. But the Apple installer won't extract it into the Applications folder. Instead I get a message "this OSX 10.11 cannot be installed on this device" It DOES NOT say there is a verification error...which it would likely say if the problem was Apple's .dmg expiration date issue. If I can't get it to extract, I can't even make a boot drive. How can I get it into the Applications folder so that I can continue the Pikify instructions???