what is SHA1 cheksum on files

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I have seen on various websites that with every file to download , there is some code like

SHA1 Checksum: 675261c60ccdc9b21fec73b96c92882d6760ceab


or some md5 hash codes

What are they used for . I haven't used them ??

[oracleguy]

They are so you can make sure the file downloaded properly and your file matches what they uploaded. So like if it later got infected with a virus, it would have a different hash.

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Does anyone checks it before executing?? Just for the info , How many times you have checked before running any file from internet.

[oracleguy]

Depends on the situation, its more common to check when on a Linux system since the tools are commonly installed.

When I write scripts that pull files off the Internet that have digest information (aka hashes), I'll usually check against it.

[primefalcon]

Depends on the situation, its more common to check when on a Linux system since the tools are commonly installed.

When I write scripts that pull files off the Internet that have digest information (aka hashes), I'll usually check against it.
It's not just for virus infection either, it checks against file corruption or really any kind of file modification