A hashing function is used to calculate a hash value.  If you insert a file into a hashing function then it should produce a value that is almost certain to be unique (there’s always the remote likelihood that no matter how good your function, you may end up with a duplicate).   The openssl command is used to access a number of functions/ciphers including sha1, base64, md5, rc4/rc5 and of course des/des3.  It is a very simple command to use, simply provide the cipher, followed by the path to the file you would like to get a hash value (aka digest) for.  So if I have a file called myfile.txt and I would like to get a digest for it I could just use the following command: openssl md5 myfile.txt At its most basic level, we’re just leveraging openssl to grab digests quickly and easily.

A checksum can be used to determine if a file has been tampered with at a later date.  To run a checksum use the following command:
openssl dgst -HASHTYPE path_to_file
HASHTYPE would then be md2, md4, md5, mdc2, rmd160, sha or sha1.  Let’s go ahead and do a checksum of our smb.conf file:
openssl dgst -md5 /var/db/smb.conf
You should then see output similar to the following:
MD5(/var/db/smb.conf)= e4b58a63c6682b298aeca3ad40734c1e
MD5(/var/db/smb.conf)= e4b58a63c6682b298aeca3ad40734c1e