If time is an issue, consider doing a wipe and fresh install then upgrade instead of upgrade in place. Apparently if you have Homebrew it gets stuck at 2 minutes, potentially for several hours.
It's worth mentioning that after the upgrade you might run into permissions problems: https://github.com/Homebrew/homebrew/blob/master/share/doc/h...
You might want to run `brew update` before updating, so `brew doctor` can help you troubleshoot issues afterwards.
rsync -rtvpl /usr/local ~/usr.local.backup
A lot of other apps do put stuff there though (when I wish they'd keep it in their own bundle).
Even worse, a lot of other apps drop stuff into /usr/bin.
You can't even do it with root:
[mason@IT-PC-MACPRO ~]$ sudo bash
Password:
[root@IT-PC-MACPRO ~]# touch /usr/bin/nope
touch: /usr/bin/nope: Operation not permitted
[root@IT-PC-MACPRO ~]# cat 'nope nope' >> /usr/bin/nope
bash: /usr/bin/nope: Operation not permittedI knew about /usr/local problem from Yosemite, though on El Capitan (same time as Yosemite, with /usr/local moved to ~/local) it was smooth as butter (I did not move /usr/local). All upgrade took about 30 minutes, and after it was done, I did sudo chown -R $(whoami):admin /usr/local and I was good to go.
I just ignored this and waited for the installer to do whatever it wanted. It took about 1 hour but everything went fine and I'm now up and running.
Whatever problems Yosemite had, they weren't caused because of "file accretion", nor would they remain after the OS is updated (as if it somehow reads old problematic files and goes back to its old buggy ways).
(That said, I had zero problems as a heavy dev+audio/video user of Yosemite, and zero too after updating to El Capitan GM -- with the exception of Cubase and NI audio units not working in Logic).