Depending on what you’re trying to do, setting boot-args may be useful.
Some examples include booting to safe-mode, verbose booting, and, new in OS X 10.11, enabling or disabling rootless.
Safe mode
Safe mode (sometimes called safe boot) is a way to start up your Mac so that it performs certain checks, and prevents some software from automatically loading or opening. Starting your Mac in safe mode does the following:
- Verifies your startup disk, and attempts to repair directory issues if needed
- Loads only required kernel extensions
- Prevents Startup Items and Login Items from opening automatically
- Disables user-installed fonts
- Deletes font caches, Kernel cache and other system cache files
Together, these changes can help resolve or isolate issues related to your startup disk. To boot into safe-mode, either hold down cmd-x after power-on, or open up Terminal.app and type in the following:
1sudo nvram boot-args="-x" ; sudo reboot
Verbose boot
If you wish to see more of the boot process, such as what you’d get if you were to boot a UNIX system, you can enable verbose booting. If you want to do this once, you can hold cmd-v after powering the machine one. If you wish to have this become the default, you can open up Terminal.app and type in the following:
1sudo nvram boot-args="-v" ; sudo reboot
Rootless
Rootless (a security mechanism making its debut in El Capitan 10.11) restricts access to certain files, even as an administrative user, such as is provided by ‘sudo’. For the time being, Apple is letting us disable rootless by setting boot-args. If you need to do this, you can open up Terminal.app and type in the following:
1sudo nvram boot-args="rootless=0" ; sudo reboot
Once you are done modifying files and are ready to enable rootless again, open Terminal.app and type in the following:
1sudo nvram -d boot-args ; sudo reboot
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