PSA: gz isn’t a generic compressed file extension


Take a look at this filename, and take a guess what it is:


If you’re like me, you assumed gz meant gzip, and therefore I could extract it with gunzip(1):

$ gunzip rootfs.gz
==> gzip: rootfs.gz: not in gzip format

Wait, so what is this file file?

$ file rootfs.gz
==> XZ compressed data

This happens constantly. Is it a mild form of obfuscation? Do people think gz is a generic catch-all for all compressed data? Was a directive passed down to convert things to use xz, but tooling wasn’t updated to output the correct extension?

If I had a cent for each time this has happened, I’d still need many more to afford a coffee. But it’s more than nothing, which is what I hope people reading this blog conclude about the quality of my posts.

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Ruben Schade is a technical writer and infrastructure architect in Sydney, Australia who refers to himself in the third person. Hi!

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