linux - Group permissions there but cannot access file? -

I have a simple FTP file on my Linux machine for a machine on my home directory and this file It was in permissions ....

  tom @ bellmachine-6745: ~ $ ---- rwx --- 1 tom tom 6 Mar 16 12:45 redtest.txt  

said that this file belongs to the group, he said that the terminal was under Tom's proprietary file Tom

But touching redtest.txt allowed me to " Permission denied "given vi redtest.txt Why did one give me "denied" permission?

I could only edit when I was allowed to do the following through the file .... chmod 670 redtest.txt

Let me file ownership Tom and Tom were members of the group. OK, the access to the group Tom members for this file was only because why should I change those keymaps, this should allow me for the first time ???

Because UNIX permissions work like this: If you are the owner of the file, The gestures are - hence the permission has not been denied. If the file was owned by someone else, e.g. Jane and Jane Group will be in Tom, Jane will be able to access it. If the existing user is not the owner of the file (Tom) nor the group is in the tow then permission for others will apply.

Note that the root user (with UID 0) ignores the permissions and is enabled to access the file with any permissions set (---------- LS output).