/usr/share/mercurial/templates/paper/notfound.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 8 9 10 11 12 | {header}
<title>Mercurial repository not found</title>
</head>
<body>
<h2>Mercurial repository not found</h2>
The specified repository "{repo|escape}" is unknown, sorry.
Please go back to the <a href="{url|urlescape}">main repository list page</a>.
{footer}
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