Here is a video explaining what a file checksum is and what is things like: sha256, sha512, md5...
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To calculate sha256 of a file with command line on Linux:
sha256sum file
To calculate sha256 of a file with command line on Windows:
certutil -hashfile filename SHA256
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0:00 intro
1:01 What is checksum?
2:23 How the checksum is calculated ?
3:48 What are sha256, md5, sha1, sha512 ?
6:23 How to calculate the checksum ?
8:05 How to calculate checksum of a file in command line ?
11:33 Why are the instructions more complicated ?
12:51 What to do if the result is different ?
14:30 Conclusion
