Linux 权限 - setuid、setgid、sticky bit - 用一个命令删除所有

Question

I'm currently doing a course on Linux Essentials, and recently I came across the setuid, setgid and sticky bit permissions.

I tried to make a practical example and run the commands to apply them on a file and a directory that I created.

I noticed that the numeric command to remove them is 'chmod 0775 ', and I thought, if all three are applied, what happens if I run the numeric command to remove them. I supposed that it would remove them sequentially but in the case of the file, it removed all of them at once.

Then I tried on the directory. The result was different there. Only the last applied permission (which was the Sticky Bit) was removed. I run the command once more and didn't do anything. None of the remaining permissions (setuid, setgid) was removed.

Why is this happening?

Thanks!

Answer 1

Sticky bits for files and directories are slightly different... For example, to remove the stick bits from a directory called "Testy" you would type:

sudo chmod g-s Testy/

Note that typing the following WOULD NOT WORK: sudo chmod 777 Testy . This below tutorial gives good worked examples and explanations, my advice would be to practice some of these examples a good few times and then it will all eventually make sense. The key thing to understand (in my opinion anyway) is the Octal system involved here in setting the permissions/bits etc, once you understand that it all falls into place.

Here is the Tutorial Link: Access Control / Sticky Bit Tutorial

Answer 2

A quick search in man chmod revealed that you need to append an extra 0 or = in front. For instance like this:

chmod 00775 target  

or like this:

chmod =775 target 

If you want to remove setuid, setgid and sticky permissions for all files recursively you can use this command:

chmod -R 00775 {.,.*}