Quick cheatsheet to know where to look when you need to rid off some startup item, app or service.
Applications that run on Startup
Property list (plist) items running on startup
Applications that launch on User Login
You should be able to add/remove most applications from your user account. Go to System preferences -> Users and groups -> Select user -> Login Items.
By console you can check in the following folders:
Applications that run on a set schedule
Check your crontab with
Check Kernel Extensions
In the command line:
Check Login and Logout Hooks
defaults read com.apple.loginwindow LoginHook
defaults read com.apple.loginwindow LogoutHook
or see both with:
/usr/libexec/PlistBuddy -c Print