localhost kumar # emerge nvidia-drivers
Calculating dependencies... done!

>>> Emerging (1 of 1) x11-drivers/nvidia-drivers-1.0.9631-r91 to /
>>> Downloading 'http://distfiles.gentoo.org/distfiles/NVIDIA-Linux-x86_64-1.0-9631-pkg2.run'
--19:24:12--  http://distfiles.gentoo.org/distfiles/NVIDIA-Linux-x86_64-1.0-9631-pkg2.run
           => `/usr/portage/distfiles/NVIDIA-Linux-x86_64-1.0-9631-pkg2.run'
Resolving distfiles.gentoo.org... 216.165.129.135, 156.56.247.195, 64.50.236.52, ...
Connecting to distfiles.gentoo.org|216.165.129.135|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 10,233,636 (9.8M) [text/plain]

100%[==============================================>] 10,233,636   228.49K/s    ETA 00:00

19:24:55 (234.57 KB/s) - `/usr/portage/distfiles/NVIDIA-Linux-x86_64-1.0-9631-pkg2.run' saved [10233636/10233636]

 * checking ebuild checksums ;-) ...                                                [ ok ]
 * checking auxfile checksums ;-) ...                                               [ ok ]
 * checking miscfile checksums ;-) ...                                              [ ok ]
 * checking NVIDIA-Linux-x86_64-1.0-9631-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-1.0.9631-r91 failed.
Call stack:
  ebuild.sh, line 1580:   Called dyn_setup
  ebuild.sh, line 665:   Called pkg_setup
  nvidia-drivers-1.0.9631-r91.ebuild, line 119:   Called linux-mod_pkg_setup
  linux-mod.eclass, line 458:   Called linux-info_pkg_setup
  linux-info.eclass, line 554:   Called die

!!! Unable to calculate Linux Kernel version
!!! If you need support, post the topmost build error, and the call stack if relevant.

!!! This ebuild is from an overlay: '/usr/portage/local/layman/sabayon'