OS X Startup Options & Boot Modes
Single User Mode
Single user mode boots OS X into a single superuser and does not enter the GUI. The terminal can be used for advanced troubleshooting, hard drive repair, file system changes etc.. It can also be used to make OS X restart as if a fresh install in order to go through the process of creating an administrator user account.
Boot into Single User mode by pressing the ⌘ command+s keys when the system is started.
Creating an Admin Account
After the sytem has booted into single user mode, mount the startup drive to access to access those files.
/sbin/mount -uw /
When OS X boots, it checks if the
.applesetupdone file exists. OS X creates this empty file when Setup Assistant is completed. Remove this file so OS X will presume that Setup Assistant has not run when it is rebooted. When the system is rebooted, Setup Assistant will launch which includes creating a new admin account.
Remove .applesetupdone / Reboot
rm /var/db/.applesetupdone reboot
Boot into Recovery mode by pressing the ⌘ command+r keys when the system is started.
View hidden files and folders in Finder
defaults write com.apple.finder AppleShowAllFiles -boolean true ; killall Finder
Hide files and folders [default]
defaults write com.apple.finder AppleShowAllFiles -boolean false ; killall Finder
When cleaning up the disk, sometimes apps leave files in these locations
System Preferences > Login Items > Users & Groups > Login Items ~/Library/Preferences/ /Library/Preferences ~/Library/Preferences /Launch Agents ~/Library/Launch Agents /Launch Daemons ~Library /Launch Daemons