evan@latop:~/iso/bsd$ ls FreeBSD-12.0-RELEASE-amd64-memstick.img.xz evan@latop:~/iso/bsd$ xz -d FreeBSD-12.0-RELEASE-amd64-memstick.img.xz evan@latop:~/iso/bsd$ ls FreeBSD-12.0-RELEASE-amd64-memstick.img
xz打包，压缩和解压
