jonah@localhost ~ $ sudo emerge -av nvidia-drivers
Password:

These are the packages that would be merged, in order:

Calculating dependencies... done!
[ebuild     U ] x11-drivers/nvidia-drivers-169.12-r10 [100.14.19-r10] USE="acpi%* distribution -custom-cflags% -gtk (-multilib)" 0 kB [1]

Total: 1 package (1 upgrade), Size of downloads: 0 kB
Portage tree and overlays:
 [0] /usr/portage
 [1] /usr/portage/local/layman/sabayon

Would you like to merge these packages? [Yes/No] yes
>>> Verifying ebuild Manifests...

>>> Emerging (1 of 1) x11-drivers/nvidia-drivers-169.12-r10 to /
 * NVIDIA-Linux-x86_64-169.12-pkg2.run RMD160 ;-) ...                     [ ok ]
 * NVIDIA-Linux-x86_64-169.12-pkg2.run SHA1 ;-) ...                       [ ok ]
 * NVIDIA-Linux-x86_64-169.12-pkg2.run SHA256 ;-) ...                     [ ok ]
 * NVIDIA-Linux-x86_64-169.12-pkg2.run size ;-) ...                       [ ok ]
 * checking ebuild checksums ;-) ...                                      [ ok ]
 * checking auxfile checksums ;-) ...                                     [ ok ]
 * checking miscfile checksums ;-) ...                                    [ ok ]
 * checking NVIDIA-Linux-x86_64-169.12-pkg2.run ;-) ...                   [ ok ]
 * Determining the location of the kernel source code
 * Unable to find kernel sources at /usr/src/linux
 * This package requires Linux sources.
 * Please make sure that /usr/src/linux points at your running kernel,
 * (or the kernel you wish to build against).
 * Alternatively, set the KERNEL_DIR environment variable to the kernel sources location
 *
 * ERROR: x11-drivers/nvidia-drivers-169.12-r10 failed.
 * Call stack:
 *   ebuild.sh, line 1664:   Called dyn_setup
 *   ebuild.sh, line 719:   Called qa_call 'pkg_setup'
 *   ebuild.sh, line 44:   Called pkg_setup
 *   nvidia-drivers-169.12-r10.ebuild, line 145:   Called linux-mod_pkg_setup
 *   linux-mod.eclass, line 465:   Called linux-info_pkg_setup
 *   linux-info.eclass, line 595:   Called die
 *
 * Unable to calculate Linux Kernel version
 * If you need support, post the topmost build error, and the call stack if relevant.
 * A complete build log is located at '/var/tmp/portage/x11-drivers/nvidia-drivers-169.12-r10/temp/build.log'.
 *

 * Messages for package x11-drivers/nvidia-drivers-169.12-r10:

 * Unable to find kernel sources at /usr/src/linux
 *
 * ERROR: x11-drivers/nvidia-drivers-169.12-r10 failed.
 * Call stack:
 *   ebuild.sh, line 1664:   Called dyn_setup
 *   ebuild.sh, line 719:   Called qa_call 'pkg_setup'
 *   ebuild.sh, line 44:   Called pkg_setup
 *   nvidia-drivers-169.12-r10.ebuild, line 145:   Called linux-mod_pkg_setup
 *   linux-mod.eclass, line 465:   Called linux-info_pkg_setup
 *   linux-info.eclass, line 595:   Called die
 *
 * Unable to calculate Linux Kernel version
 * If you need support, post the topmost build error, and the call stack if relevant.
 * A complete build log is located at '/var/tmp/portage/x11-drivers/nvidia-drivers-169.12-r10/temp/build.log'.
 *
jonah@localhost ~ $