md5sum Command in Linux with Examples

Usage:
md5sum [OPTION]… [FILE]…

The MD5 message-digest algorithm is a widely used cryptographic hash function that produces a 128-bit (16-byte) hash value.Two non identical files will never have the same md5sum value.However, it has since been shown that MD5 is not collision resistant;[3] as such, MD5 is not suitable for applications like SSL certificates or digital signatures that rely on this property.

Here’s the listing of example usage of “md5sum” command:

1. To calculate md5sum(md5sum file_path):

sanfoundry-> md5sum out.txt 
fa328c3f84352dc7ff5e32bba2ac833c  out.txt

Note
md5sum command is not usable for the directories.

2. To compute and verify checksum of files(md5sum -c file_path):

sanfoundry-> md5sum *.txt 
d41d8cd98f00b204e9800998ecf8427e  1.txt
743268534af6fb128bf4dd7f4914b1c8  2.txt
d41d8cd98f00b204e9800998ecf8427e  link.txt
fa328c3f84352dc7ff5e32bba2ac833c  out.txt
sanfoundry-> md5sum *.txt > x.md5
sanfoundry-> md5sum -c x.md5 
1.txt: OK
2.txt: OK
link.txt: OK
out.txt: OK

“-c” option checks the status of the files and if there is any change it gives error.

sanfoundry-> vi 1.txt 
sanfoundry-> md5sum -c x.md5 
1.txt: FAILED
2.txt: OK
link.txt: OK
out.txt: OK
md5sum: WARNING: 2 computed checksums did NOT match

If link.txt is the link file of 1.txt then it also get changed and md5sum also FAILED to cross verify it.

sanfoundry-> vi 1.txt 
sanfoundry-> md5sum -c x.md5 
1.txt: FAILED
2.txt: OK
link.txt: FAILED
out.txt: OK
md5sum: WARNING: 2 computed checksums did NOT match

3. To read in binary mode(md5sum -b file_path):

sanfoundry-> md5sum 1.txt 
764efa883dda1e11db47671c4a3bbd9e  1.txt
sanfoundry-> md5sum -b 1.txt 
764efa883dda1e11db47671c4a3bbd9e *1.txt
sanfoundry-> md5sum --binary 1.txt 
764efa883dda1e11db47671c4a3bbd9e *1.txt

“-b” option is equivalent to “–binary” option.
Treat all input files as binary. This normally does not make any difference on UN*X systems but some systems have a different internal and external representation of texts (especially the end-of-line characters).

4. To read in text mode(md5sum -t file_path):
Treat all input files as text files. This is the reverse option to –binary.

sanfoundry-> md5sum -t 1.txt 
764efa883dda1e11db47671c4a3bbd9e  1.txt

5. To print version information on standard output then exit(md5sum -v):

sanfoundry-> md5sum --version
md5sum (GNU coreutils) 8.13
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
 
Written by Ulrich Drepper, Scott Miller, and David Madore.

Sanfoundry Global Education & Learning Series – 1000 Linux Tutorials.