Unable to downgrade from High Sierra

[AeroZ]

Hi!

I'm trying to downgrade from High Sierra to either Sierra or El Capitan. The problem is that after I download the installers they fail verification. That's even before I try to create any USB bootable installer. If I ignore this, create USB bootable installer and try to install the OS then in the end of installation I get an error that the installation failed verification.

user$ hdiutil verify /Applications/Install\ macOS\ Sierra.app/Contents/SharedSupport/InstallESD.dmg
Checksumming Protective Master Boot Record (MBR : 0)…
Protective Master Boot Record (MBR :: verified   CRC32 $A9C57BFE
Checksumming GPT Header (Primary GPT Header : 1)…
 GPT Header (Primary GPT Header : 1): verified   CRC32 $D77F2898
Checksumming GPT Partition Data (Primary GPT Table : 2)…
GPT Partition Data (Primary GPT Tabl: verified   CRC32 $6D9EBA8C
Checksumming  (Apple_Free : 3)…
                    (Apple_Free : 3): verified   CRC32 $00000000
Checksumming EFI System Partition (C12A7328-F81F-11D2-BA4B-00A0C93EC93B : 4)…
..
EFI System Partition (C12A7328-F81F-: verified   CRC32 $B54B659C
Checksumming disk image (Apple_HFS : 5)…
.............................................................................
          disk image (Apple_HFS : 5): calculated CRC32 $D70CB5DC, expected   CRC32 $C16DFE8C
Checksumming  (Apple_Free : 6)…
..............................................................................
                    (Apple_Free : 6): verified   CRC32 $00000000
Checksumming GPT Partition Data (Backup GPT Table : 7)…
..............................................................................
GPT Partition Data (Backup GPT Table: verified   CRC32 $6D9EBA8C
Checksumming GPT Header (Backup GPT Header : 8)…
...............................................................................
  GPT Header (Backup GPT Header : 8): verified   CRC32 $38EE2A7A
...............................................................................
calculated CRC32 $72ECC31E, expected   CRC32 $3B94F102
hdiutil: verify: checksum of "/Applications/Install macOS Sierra.app/Contents/SharedSupport/InstallESD.dmg" is INVALID
hdiutil: verify failed - invalid checksum

I get exactly the same error for El Capitan installer.

Any ideas how to fix this and successfully downgrade?

Thanks!

 

[Fishrrman]

Try this (just try it, and get back to us):

1. Download the free app "Boot Buddy" from here:
https://sqwarq.com/boot-buddy/

2. Take a USB flashdrive 8gb or 16gb. Use Disk Utility to erase it Mac OS extended with journaling enabled.

3. Open Boot Buddy, select the installer (either Low Sierra or El Cap), then select the USB target drive, then let BB "do it's thing". It will take a little while.

4. What do you have as a result?

 

[AeroZ]

Try this (just try it, and get back to us):

1. Download the free app "Boot Buddy" from here:
https://sqwarq.com/boot-buddy/

2. Take a USB flashdrive 8gb or 16gb. Use Disk Utility to erase it Mac OS extended with journaling enabled.

3. Open Boot Buddy, select the installer (either Low Sierra or El Cap), then select the USB target drive, then let BB "do it's thing". It will take a little while.

4. What do you have as a result?

I actually got it sorted. Earlier today I did an AHT run and it reported that one memory is bad. It was kind of odd because my computer was working fine. So I tested the two dimms with memtest86 and one of them was indeed giving me errors so I left the one with errors out.
So about an hour ago I thought I'd try to download the installer again just in case. Verification result:

hdiutil: verify: checksum of "/Applications/Install OS X El Capitan.app/Contents/SharedSupport/InstallESD.dmg" is VALID

It's odd that I was able to install High Sierra in recovery after initially failing El Capitan install. But now after having my mac setup from a clean install I'm not sure if I'm even willing to go through the hassle of clean installing El Capitan anymore. I'll try High Sierra for a few days and keep my eye on the stability and then decide.

Anyways, thanks for your time and help. Hope this thread helps somebody else with similar issues.