-<!ENTITY url.linux.kernel "http://www.kernel.org">
-<!ENTITY url.debian "http://www.debian.org">
-<!ENTITY url.redhat "http://www.redhat.com">
-<!ENTITY url.gentoo "http://www.gentoo.org">
+<!ENTITY url.linux.kernel "http://www.kernel.org/">
+<!ENTITY url.debian "http://www.debian.org/">
+<!ENTITY url.redhat "http://www.redhat.com/">
+<!ENTITY url.centos "http://www.centos.org/">
+<!ENTITY url.gentoo "http://www.gentoo.org/">