02checksum 校验

1. checksum 校验和

sha256sum	file
c4fd0632ce15a7d56e1d174176456943bd48306f9d35bcecbcb0a1dc49088e23	rhel-8.9-x86_64-dvd.iso
e33d7b1ea7a9e2f38c8f693215dd85254c3a4fe446f93f563279715b68d07987	CentOS-7-x86_64-DVD-2009.iso
30fd8dff2d29a384bd97886fa826fa5be872213c81e853eae3f9d9674f720ad0	rhel-8.3-x86_64-dvd.iso
8cb0dfacc94b789933253d5583a2fb7afce26d38d75be7c204975fe20b7bdf71	rhel-8.6-x86_64-dvd.iso