% find a/ | cpio -o | gzip -c > alpha.gz
% find b/ | cpio -o | gzip -c > bravo.gz
% cat alpha.gz beta.gz > charlie.gz
% gunzip charlie.gz
Now I get file charlie, which should be a concatenated cpio archive. But cpio -id < charlie only extract the content of a/. How could I get b/?
Added: The size of charlie equals alpha plus bravo. And egrep some key words showed that charlie sure contains data of bravo.