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In Linux system, assume that there is user 'A' (non-root user who has ssh login permission).

'A' owns an executable file "A.out".

I want to allow 'A' to read/execute "A.out"

However, I don't want 'A' to change permission of "A.out"

as a root user, how can I enforce this?(in Ubuntu server)

thank you in advance.

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up vote 3 down vote accepted

The only two ways you can enforce this are:

  1. Change the file's owner to root or another user.

  2. Use SELinux/AppArmor/SMACK to deny the chmod usage.

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Just to add, when/if you do change file's owner to root, make sure that "userA" has read-only access to file by being in group-owner group of file. – phoops Jun 11 '14 at 7:10
    
@edvinas.me: Or by being in the file's ACL. – grawity Jun 11 '14 at 7:12
    
it seems that if the owner of 'A.out' is root and group of 'A.out' is 'A' and if I give the permission of 'A.out' ---r-x---, it works as I want. A can RX the file 'A.out' but cannot change the permission. Am i right? – daehee Jun 11 '14 at 7:19

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