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What I understand is, you could change the permission of a file for its owner by, say

chmod u=0 file.txt

In this case, we removed r, w and x permission for the owner of this file.

But under what circumstances would we like to do that? If you are the file owner, why would you like to downgrade the permission of your own file?

closed as too broad by Rui F Ribeiro, msp9011, Stephen Harris, icarus, Ouki Dec 31 '18 at 1:08

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    For the very same reason people use skins for their mobiles. Because you can. Because it protects them from mishandling. – Rui F Ribeiro Dec 28 '18 at 5:03
  • Thanks Rui! Yeah I later figured out that, I can simply "lock" the file by removing w permission for myself if I would never want to edit it again. That's a use case I guess – Hang Dec 29 '18 at 5:12
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It is not against an intelligent actor, because as owner, they could chmod() the file any time, giving their permissions back.

It might be useful against programs, if you want to avoid your own programs to play with some of your file on any reason.

However, typically it is more feasible to simply move that file away.

It might be also useful, if the underlying filesystem driver doesn't support chmod(). For example, davfs or vfat file modes are determined by the mount flags and not by the filesystem metadata.

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