md5sum: no properly formatted MD5 checksum lines found

md5sum is for printing or checking MD5 (128-bit) checksums. One can download a file on Internet and also download its checksum. The md5sum command can, then, be used to verify whether the file has been correctly received. Also, while putting a file file for download, the checksum is also put in a separate file so that users can download both and check the file using checksum.
Checking files using md5 checksum

The command usage is

md5sum -c

where checksum_file is a specially formatted text file. Each line of has the following format

md5sum_checksum space space file_name

where,
is the md5 checksum,
is the space character, 0x20