XML to XSD tool for linux
In the past I have used Trang : http://www.thaiopensource.com/relaxng/trang.html
Its old and basic but i find it generates cleaner schemas than other tools (e.g. XMLSpy)
You can create a DTD from XML using DTDGenerator from the saxon project. Then you can convert this to a XSD using W3C's dtd2xsd.pl. See Free DTD to XSD conversion utility?.