/usr/share/mercurial/templates/raw/graphnode.tmpl is in mercurial-common 4.5.3-1ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 | changeset: {node|short}
user: {author|person}
date: {date|age}
summary: {desc|firstline|nonempty}
{branches%branchname}{tags%tagname}{bookmarks%bookmarkname}
node: ({col}, {row}) (color {color})
{edges%graphedge}
|