/usr/lib/python2.7/dist-packages/IPython/frontend/html/notebook/templates/layout.html is in ipython-notebook 0.12.1+dfsg-0ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/python2.7/dist-packages/IPython/frontend/html/notebook/templates/../../../../../../../../share/pyshared/IPython/frontend/html/notebook/templates/layout.html