OS X El Capitan grief

Note: OS X El Capitan changed permissions on /usr thus breaking access to MacTex's expected path to applications /usr/texbin. On El Capitan you may need to add /Library/TeX/texbin to $PATH. Do so via a shell/terminal e.g. sudo nano /etc/paths. Might also need to delete previous package in /usr/local/texlive. Might also need to change "System Preferences/Security & Privacy/Allow apps downloaded from:" Change to "Anywhere". Possibly unrelated, but on OS X may also need to install legacy Java (link).

Troubleshoot installations? Type command L from the first screen of the installer to open the log window so you can see error messages.

The MacTeX site strongly recommended download via Safari. A warning I ignored at my peril, because downloads on OS X via Chrome produced files with wrong checksums! Proof below...

$ md5 mactex-20150613.pkg
MD5 (mactex-20150613.pkg) = 6aa62533c5aa0bc3d25b166cd67741fb

Yet another download via Chrome produces another (different) checksum.

$ md5 mactex-20150613.pkg
MD5 (mactex-20150613.pkg) = 5bde8e023873ad2b70b28ee28f170f7a

Whereas the stated package checksum for the MacTeX package [14 June 2015], should have been
= bf579a512d31253d828591fdb3644dca

At last a version downloaded via Safari yielded the following...

$ md5 mactex-20150613.pkg
MD5 (mactex-20150613.pkg) = bf579a512d31253d828591fdb3644dca

Lesson learned "do do do run the MD5 file checksum" & "don't use Chrome on OS X for large downloads".

Note: The file downloaded using Safari will also preserve the creation data / date modified, whereas large files downloaded using Chrome will be timestamped today and vary in file size from the original and multiple attempts.