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comment What mechanism enforces user permissions in Unix/Linux?
When we try to do something that requires sudo access and we don't have it, then OS refuses this is because we are trying execute operation on an inode, which is not our's. For example [user1@localhost ~]$ sudo chown -R user2:group2 Documents/ This will ask for sudo password and refuses if we don't have, just because inode permissions of /usr/bin/chown file does not belong to user1 in any ways (owner/group/other). Unix kernel can read and load a file into memory for execution only if it has access permission on the inodes the file points to.