Since macOS High Sierra 10.13, the operating system applies a stricter security policy to software that requires kernel extensions (kexts). The DisplayLink driver installation includes a system extension (DisplayLinkDriver.kext) that is affected by this policy.
As a result, the user now has to explicitly enable this system extension in the Security & Privacy system preference after installation and before the DisplayLink software is allowed to run.
How to check if the DisplayLink Kext is blocked
You can check if the DisplayLink Kext is blocked by opening the System Report (Apple menu -> About) and select Extensions on the left pane and look for DisplayLinkDriver.kext. Check the "Loaded" column. See the screenshot below, which shows the Kext blocked.
If this is set to "No" then the kext is blocked and needs to be enabled following the steps below.
Enabling the DisplayLink Kext
Please note: It's only possible to enable the system extension in the 30 minutes following the installation. A new installation can be run to reset this timer.
At the end of the installation, the operating system should display a "System Extension Blocked after installation" warning and ask the user to enable the DisplayLink extension(Figure 1):
Important: This warning is not always shown. Even if it is not shown, for new installations the user must enable the kernel extension to use the DisplayLink product.
The setting is available by choosing System Preferences from the Apple Menu and then clicking on the Security & Privacy panel (Figure 2).
Follow Figure 3 - Figure 5 to enable the DisplayLink Software to run on the system. Please note that the interface presented may be different if multiple software require user authorisation.
Occasionally popup from Figure 1 may not be displayed and after the installation and reboot the DisplayLink additional monitors might not be functional. To resolve this it is required to manually allow the DisplayLink driver to be loaded on system following Figure 2 – Figure 4 and reboot the system at the end.Important notes:
- On some systems, the security clearance may not take automatically effect and the DisplayLink Software will still not be functional after rebooting. In this case, simply run the installer process again to ensure all the software is correctly started. This issue has been raised by DisplayLink to Apple with bug ID 33133825.
- Once the user approval has been granted, following installations of the DisplayLink software will not require further approval. This also means that systems upgraded to High Sierra while the DisplayLink software was installed won't require authentication.
- The Apple tech note linked below contains instructions about how to install third party kexts in a managed corporate environment.
- The detailed description of this macOS change is documented at https://developer.apple.com/library/content/technotes/tn2459