MacTeX contains three pieces. The first, TeX Live, is a gigantic collection of command line programs like TeX, LaTeX, XeTeX, LuaTeX, and associated style and class files, fonts, documentation, etc. It is installed in /usr/local/texlive/2020 and thus hidden from most users. This software does the actual typesetting.
The second piece is Ghostscript, which can process postscript, eps, and pdf files. This is a command line program which users do not see directly. It is installed in /usr/local/bin with support files in various /usr/local folders. Most pieces of TeX Live do not require Ghostscript.
The third piece contains four GUI programs: TeXShop, TeX Live Utility, BibDesk, and LaTeXiT. These are the programs users actually see and use to interact with TeX. They are installed in /Applications/TeX, together with a small amount of documentation telling new users how to get started.
MacTeX-2020 supports macOS 13, 14, and 15, High Sierra, Mojave, and Catalina. In particular, the TeX Live binaries were compiled on High Sierra. TeX Live labels these binaries x86_64-darwin.
However, Mojca Miklavec compiled the 2020 binaries for older systems on Snow Leopard; her binaries are also in TeX Live. These binaries require Intel processors for systems 10.6 (Snow Leopard) and higher; TeX Live labels these binaries x86_64-darwinlegacy.
Most Mac users with older systems already have versions of Ghostscript and the GUI programs which work on their systems. They only need to update TeX Live. This is not possible with the MacTeX install package, but it is easy to do using the Unix install script which TeX Live supplies.
How to install TeX Live with the Unix Script
To begin the installation, click the link install-tl-unx.tar.gz to download this item.
Your Mac should automatically unzip it and you will find a file named "install-tl-unx.tar" in your downloads folder. Move this file to your desktop or your home folder and click to untar it, producing a folder. It is very important to check the name of this folder. A typical name is "install-tl-20200527". The numbers at the end give a date in the form year:month:day. Check that the year is 2020.
If it is 2019, then you received last year's install script because the mirror assigned to you was not yet updated. Wait a few days and try again.
Open Terminal in /Applications/Utilities. Type the word "cd" without quotes and a space in the resulting window. Then drag the install-tl folder created previously into the window and drop it there. This will add some text after the "cd". Activate the Terminal window by clicking in it if necessary, and press RETURN. Terminal will "change directory" to the install-tl folder.
Type "sudo ./install-tl --gui tcl" without the quotes, and press return. You might want to copy and paste this command rather than typing it because Unix if very picky; the last item is TCL, but in small letters.
You will be asked for your password. If you have admin status (and most users on single owner machines do), type your ordinary password.
A window will appear showing the TeX Lion. After a few moments, it will be replaced with a window titled "TeX Live 2020 Installer". This window contains a pull down menu labeled "Default paper size" with default value "A4." If you are in a region where Letter Size paper is used, change "A4" to "Letter" in this menu.
All other defaults will be correct for the Macintosh. If your system is 10.12 or earlier, the "x86_64-darwinlegacy" binaries will be selected for installation; otherwise the "x86_64-darwin" binaries will be selected. So just push the Install button.
Occasionally, users have reported an error when using the above "install-tl" command. If that happens to you, type "sudo ./install-tl --gui text" without the quotes, and press return. The TeX Lion described in the following paragraph will not appear, and you'll get a slightly longer display with several questions. But all of the default answers are correct, so the only question which matters is the one about paper size. If you use "letter" size rather than "A4", select that answer. Then select "install" and skip the next paragraph. Everything else will work the same.
The install window will display a long list of packages as each is downloaded, uncompressed, and installed. This process may take one to two hours or more. In the end, some additional messages will be printed, but these can be ignored because the final step will do them automatically. You now have TeX Live 2020.
Installation is not quite done; a small data structure must be added so the GUI applications can easily find the TeX Distribution. Click the link TeXDist-2020 to download a small install package. Find this package in your Downloads Folder and drag it to the desktop. Double click to install. Installation takes only a minute and your TeX Live 2020 installation is complete.
Changing the Install Location
The installer has a button allowing users to select the location where TeX is installed. If you pick a location in your home directory, the "sudo" item in the command "sudo ./install-tl" listed earlier can be omitted, and then admin permission is not required to install TeX. Users who make this change should NOT install "TeXDist Installer" because this package is configured for the default location of TeX. These users will need to obtain and configure GUI programs on their own. Configuring these programs should not be difficult for knowledgable users, but we do not provide support for this option.