MacOS – How to Remove or Edit a synthetic.conf File in etc/

There are several problems with the script you posted.

Don't remove /Users/Shared - iTunes needs it and will fail on certain store and sharing operations.

dscl on Lion will still whine if you start it (it's looking for the missing plist) - even if you launch /System/Library/LaunchDaemons/com.apple.opendirectoryd.plist as Ingmar Hupp has suggested.

I've never been one to worry about cleaning up the groups since I'm deleting user 501. The system will just add UID 501 back into the Admin and Staff groups the next time the Setup Assistant boots, so I do the following: (assume the short name of the user 501 is test)

1. ⌘+S
2. /sbin/mount -uw /
3. cd /var/db/dslocal/nodes/Default/users/
4. rm test.plist
5. rm -rf /Users/test
6. rm /var/db/.AppleSetupDone
7. halt

I do use the official Users & Groups Preference Pane to delete all users except 501 and/or create the test user as 501 as needed since launchd can have jobs stuck if the users you are clearing aren't trivial users set up for simple updates as your case allows.

I would avoid saving a WiFi password or setting up WiFi outside the user account or use ethernet for your updates if you want to be fastidious about leaving as little of your settings behind (especially if the SSID/name isn't generic like Apple Network or has WEP/WPA keys).

The normal way to do things is as per your third choice ie use an admin account to install things.

However Homebrew's normal setup does not stick to normal Unix conventions of installing excutables as root or a special user which would allow equal access of the installed code to all users, it is designed so that you do installs as one user and so do not need to use sudo/su for anything. However to do this it needs to make /usr/local writeable by the normal user and you need admin rights to that as in the way you did in the end. I think Homebrew really is designed for a computer which only one person uses and has admin rights.

If you do not want to (or cannot) set your user to admin then there are two ways

1. As per the instructions you quote "If this sucks for you then you can install Homebrew in your home directory" Then the access to ~/usr/local is always for the user
2. A version of your 3. The Homebrew script leaves /usr/local and all under it owned by the user doing the installation. With the admin user you can change the owner to your normal user by chown -R usr /usr/local

Yes there is only one /usr/local in the file system. Each path is unique. The way to have the "same" directory for different users is to put the directories under your home directory e.g. ~/usr/local