What does this command do?

sudo nvram boot-args="kext-dev-mode=1"

The command has nothing to with the serial port as such.

The "sudo" part means that you want to run the command that follows with superuser privileges.

The command is nvram, which is a command that allows you change variables in the NVRAM that is used by the firmware and kernel during boot of the computer.

The variable here is "kext-dev-mode" which is being enabled by setting it to 1. Ordinary kernel extensions (mainly drivers) must be signed by the developer, and the developers certificate needs to be signed by Apple - otherwise the kernel extension cannot be loaded.

The "kext-dev-mode" is intended for development scenarios where you want to test unsigned kernel extensions. Thus allowing these to be loaded without testing if they are indeed signed.

However, kext-dev-mode is no longer used for anything. On OS X El Capitan and newer it does absolutely nothing.

  • 1
    Not true. kext-dev-mode only does nothing if SIP is off.
    – GDP2
    May 9 '18 at 2:43
  • Have you actually tried? With SIP off you can load unsigned extensions without kext-dev-mode.
    – jksoegaard
    May 9 '18 at 5:42
  • Well, I haven't disabled both SIP and kext-dev-mode. I've used them both together and been able to load unsigned kexts. I'm also going off what I've heard from others around the net.
    – GDP2
    May 9 '18 at 15:50
  • 1
    You do realize that I linked to Apple's own documentation for the fact that kext-dev-mode is obsoleted and no longer serves a function? - I'm not going off what I've heard from others around the net. You can just disable SIP and that's all that is required..
    – jksoegaard
    May 9 '18 at 19:27

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