Many users have experienced a slower OS X experience after updating to El Capitan. Slowness can come from a number of sources, including the re-indexing of Spotlight, which occurs in the hours after an installation of El Capitan. So, 24 hours of slowness after you’ve updated to El Capitan is not unusual and it is temporary. Jun 21, 2016 Installing El Capiton on an old Mac Book Pro today, I received the error: OS X could not be installed on your computer. No packages were eligible for install. Contact the software manufacturer for assistance. Quit the installer to restart your computer and try again.

1. El Capitan Unable To Install
2. El Capitan Reinstall

Hello,
I want to install El Capitan in Virtualbox 5.0.16 for testing use.El Capitan is my host system too.
In several postings I have found a script to create El Capitan.iso.
But the installation process stops showing the 2.0 shell within less than a second.
I followed the hints like to change the chipset to PIIX3 or tried to edit the startup.nsh for to add some recommended published lines. Perhaps I did.n’t quite get it, because the edition of this file failed.
Another solution was reported to start the installation with Yosemite or Mavericks and then after successful installation start an upgrade process.
Unfortunately I have an installation dvd of Snow Leopard only. With this there is another problem, because the virtualized hard disk isn’t recognized just at the beginning of the installation and so this installation fails too.
There were several reports that El Capitan is not well supported by Virtualbox and another reason for problems should be that Apple changed MBR to GPT. I have read other postings in this board but didn’t find a real solution for me. According to other reports the virtualization of El Capitan worked well obviously after having created the iso file successfully.
So has anybody some hints how to manage the boot failure described above and maybe can post a helpful script of commands?
Thank you in advance.

These advanced steps are primarily for system administrators and others who are familiar with the command line. You don't need a bootable installer to upgrade macOS or reinstall macOS, but it can be useful when you want to install on multiple computers without downloading the installer each time.

What you need to create a bootable installer

• A USB flash drive or other secondary volume formatted as Mac OS Extended, with at least 14GB of available storage
• A downloaded installer for macOS Big Sur, Catalina, Mojave, High Sierra, or El Capitan

Download macOS

• Download: macOS Big Sur, macOS Catalina, macOS Mojave, or macOS High Sierra
  These download to your Applications folder as an app named Install macOS [version name]. If the installer opens after downloading, quit it without continuing installation. To get the correct installer, download from a Mac that is using macOS Sierra 10.12.5 or later, or El Capitan 10.11.6. Enterprise administrators, please download from Apple, not a locally hosted software-update server.
• Download: OS X El Capitan
  This downloads as a disk image named InstallMacOSX.dmg. On a Mac that is compatible with El Capitan, open the disk image and run the installer within, named InstallMacOSX.pkg. It installs an app named Install OS X El Capitan into your Applications folder. You will create the bootable installer from this app, not from the disk image or .pkg installer.

Use the 'createinstallmedia' command in Terminal

1. Connect the USB flash drive or other volume that you're using for the bootable installer.
2. Open Terminal, which is in the Utilities folder of your Applications folder.
3. Type or paste one of the following commands in Terminal. These assume that the installer is in your Applications folder, and MyVolume is the name of the USB flash drive or other volume you're using. If it has a different name, replace MyVolume in these commands with the name of your volume.

Big Sur:*

Catalina:*

Mojave:*

High Sierra:*

El Capitan:

* If your Mac is using macOS Sierra or earlier, include the --applicationpath argument and installer path, similar to the way this is done in the command for El Capitan.

After typing the command:

1. Press Return to enter the command.
2. When prompted, type your administrator password and press Return again. Terminal doesn't show any characters as you type your password.
3. When prompted, type Y to confirm that you want to erase the volume, then press Return. Terminal shows the progress as the volume is erased.
4. After the volume is erased, you may see an alert that Terminal would like to access files on a removable volume. Click OK to allow the copy to proceed.
5. When Terminal says that it's done, the volume will have the same name as the installer you downloaded, such as Install macOS Big Sur. You can now quit Terminal and eject the volume.
   

Use the bootable installer

Determine whether you're using a Mac with Apple silicon, then follow the appropriate steps:

Apple silicon

1. Plug the bootable installer into a Mac that is connected to the internet and compatible with the version of macOS you're installing.
2. Turn on your Mac and continue to hold the power button until you see the startup options window, which shows your bootable volumes.
3. Select the volume containing the bootable installer, then click Continue.
4. When the macOS installer opens, follow the onscreen instructions.

Intel processor

El Capitan Unable To Install

1. Plug the bootable installer into a Mac that is connected to the internet and compatible with the version of macOS you're installing.
2. Press and hold the Option (Alt) ⌥ key immediately after turning on or restarting your Mac.
3. Release the Option key when you see a dark screen showing your bootable volumes.
4. Select the volume containing the bootable installer. Then click the up arrow or press Return.
   If you can't start up from the bootable installer, make sure that the External Boot setting in Startup Security Utility is set to allow booting from external media.
5. Choose your language, if prompted.
6. Select Install macOS (or Install OS X) from the Utilities window, then click Continue and follow the onscreen instructions.

Learn more

A bootable installer doesn't download macOS from the internet, but it does require an internet connection to get firmware and other information specific to the Mac model.

El Capitan Reinstall

For information about the createinstallmedia command and the arguments you can use with it, make sure that the macOS installer is in your Applications folder, then enter the appropriate path in Terminal: