Verify file integrity with md5sum in Linux

1. Introduction

The MD5 algorithm is often used to verify the integrity of network file transmission and prevent file tampering. The full name of MD5 is the Message Digest Algorithm (Message-Digest Algorithm 5). This Algorithm computes information of any length by bit, generate a "fingerprint" (or "Message Digest") with a binary length of 128 bits (32 bits in hexadecimal format "), different files may generate the same message digest.

In linux or Unix, md5sum is a tool program used to calculate and verify the file message digest. Generally, after Linux is installed, the md5sum tool runs directly on the command line terminal.

2. Command Format

Md5sum [OPTION]... [FILE]...

3. Command Options

-B or -- binary: treats the input file as a binary file.
-T or -- text: view the input file as a text file (default ).
-C or -- check: used to read md5 information from the file to check file consistency. (For more information, see info)
-- Status: This option is used with check. The check result is displayed based on the returned value instead of output during check.
-W or -- warn: check whether the input md5 information is invalid during check. If yes, the corresponding information is output.

4. Example

(1) generate the md5 value of a file as follows:

[Root @ bkjia www.bkjia.com] # md5sum p182> cc.txt

In this example, the md5check file cc.txt of p182is generated. Open cc.txt and you can see the following content:

[Root @ bkjia www.bkjia.com] # cat cc.txt
Dd05e55e3aca2d39e49a1a7d1b3fd404 p182

(2) check whether the two files are the same. You can compare the md5 values of the two files.

[Root @ bkjia www.bkjia.com] # md5sum p182> ee.txt
[Root @ bkjia www.bkjia.com] # cat ee.txt
0f0b000b096ac947d6067466cc60ffd0 p182

[Root @ bkjia www.bkjia.com] # md5sum p183> ff.txt
[Root @ bkjia www.bkjia.com] # cat ff.txt
Dd05e55e3aca2d39e49a1a7d1b3fd404 p183

(3) determine whether a file is modified and use md5 to determine

[Root @ bkjia www.bkjia.com] # md5sum p182> cc.txt
[Root @ bkjia www.bkjia.com] # cat cc.txt
0f0b000b096ac947d6067466cc60ffd0 p182

 

Modify the p182 file:

[Root @ bkjia www.bkjia.com] # vi p182

Compare with the original md5 result:
[Root @ bkjia www.bkjia.com] # md5sum p182-c cc.txt
Md5sum: p182: no properly formatted MD5 checksum lines found
P182: FAILED
Md5sum: WARNING: 1 of 1 computed checksum did NOT match

The md5 result after modification is as follows:

[Root @ bkjia www.bkjia.com] # md5sum p182> dd.txt
[Root @ bkjia www.bkjia.com] # cat dd.txt
521e87e3331e94a483aec6bf21339845 p182