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when I try to install from the USB drive it says "this copy of the install OS X El Capitan application can't be verified. it may have been corrupted or tampered with during downloading.
iMac 27″ 5K, macOS 10.15
Have you tried downloading El Capitan again and then trying to make the USB.
When did you make this bootable USB for El Capitan, in October 2019 the certificates for
several Mac OS X's and macOS's expired and will not install, this could be the source of
the error message.
Apple did release updated versions of these expired installers so if you haven't already done so
here are the instructions.
How to upgrade to OS X El Capitan – Apple Support
Go to Section 4 and click on Download OS X El Capitan.
This downloads InstallMacOSX.dmg to your Downloads folder.
The next section can only be done on a mac that is capable of running El Capitan,
a mac that came preinstalled with an OS later than El Capitan will refuse to do the next bit.
When downloaded open to InstallMacOSX.pkg, double-click on
that and an installation window will open, this does not install El Capitan
but converts the InstallMacOSX.pkg to the Install OS X El Capitan.app which
you will find in your Applications folder, it should be 6.2GBs in size.
(If the installation window asks which disk you want to install to, you must pick
the disk that you are booted to at the time. Not any internal or external disk that
you want to eventually install El Capitan on, that is for later.)
To create a bootable USB installer disk use the Install OS X El Capitan.app
in the Applications folder and the createinstallmedia command in the Terminal app.
Read the instructions here,
How to create a bootable installer for macOS – Apple Support
Have you tried downloading El Capitan again and then trying to make the USB.
When did you make this bootable USB for El Capitan, in October 2019 the certificates for
several Mac OS X's and macOS's expired and will not install, this could be the source of
the error message.
Apple did release updated versions of these expired installers so if you haven't already done so
here are the instructions.
How to upgrade to OS X El Capitan – Apple Support
Go to Section 4 and click on Download OS X El Capitan.
This downloads InstallMacOSX.dmg to your Downloads folder.
The next section can only be done on a mac that is capable of running El Capitan,
a mac that came preinstalled with an OS later than El Capitan will refuse to do the next bit.
When downloaded open to InstallMacOSX.pkg, double-click on
that and an installation window will open, this does not install El Capitan
but converts the InstallMacOSX.pkg to the Install OS X El Capitan.app which
you will find in your Applications folder, it should be 6.2GBs in size.
(If the installation window asks which disk you want to install to, you must pick
the disk that you are booted to at the time. Not any internal or external disk that
you want to eventually install El Capitan on, that is for later.)
To create a bootable USB installer disk use the Install OS X El Capitan.app
in the Applications folder and the createinstallmedia command in the Terminal app.
Read the instructions here,
How to create a bootable installer for macOS – Apple Support
tried making bootable USB El Capitan install disk
