git をコンパイルすると、次のエラーが発生します。
make[2]: Leaving directory `/home/xxx/git-master'
XMLTO git-add.1
xmlto: /home/xxx/git-master/Documentation/git-add.xml does not validate (status 3)
xmlto: Fix document syntax or use --skip-validation option
I/O error : Attempt to load network entity http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd
/home/xxx/git-master/Documentation/git-add.xml:2: warning: failed to load external entity "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"
D DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"
I/O error : Attempt to load network entity http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd
warning: failed to load external entity "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"
validity error : Could not load the external subset "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"
Document /home/xxx/git-master/Documentation/git-add.xml does not validate
make[1]: *** [git-add.1] Error 13
make[1]: Leaving directory `/home/xxx/git-master/Documentation'
make: *** [doc] Error 2
主な問題は何ですか?