Understanding Group Permissions

Question

I'd appreciate help with a couple questions regarding standard file permissions. Assume that I'm not using access control lists.

If a file is associated with multiple groups, must all groups have the same permissions?
If the group permission includes write access, can any member of any group the file is associated with change the file permissions? Can such a person change the file owner?
Say now the file permission is rwxr----- (owner can do everything, but group members can only read). I am in the group associated with the file. I am also the file owner. Which permission am I granted? Read-only, or rwx?

By the way, I have not found a good resource describing file permissions. If anyone can point to helpful resources, that would appreciated as well. — Tosh, Jun 19 '15 at 05:58
I was stupid. I did not realize a file can only have one group owner. — Tosh, Jun 19 '15 at 06:21

score 3 · Accepted Answer · edited Apr 13 '17 at 12:23

3

A file can only have one group

Only the owner of the file can do that.

$ sudo touch ~/tmp/test
$ sudo chown root:aboettger ~/tmp/test
$ ls -la ~/tmp/test
-rw-rw-r-- 1 root aboettger 853 Jun 19 08:26 /home/aboettger/tmp/test
$ chmod g-w ~/tmp/test 
chmod: changing permissions of 'test': Operation not permitted

You have rwx access rights

And you should read this. ;)

edited Apr 13 '17 at 12:23

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answered Jun 19 '15 at 06:18

A.B.

90,397

Thanks A.B. So this means I as the file owner can assign r-- group permissions to a file, and someone in the group can change it to rwx? – Tosh Jun 19 '15 at 06:23
Sorry, no, I have corrected my answer – A.B. Jun 19 '15 at 06:26
See my corrected answer, sorry again. – A.B. Jun 19 '15 at 06:30
Just saw the link - interesting. – Tosh Jun 19 '15 at 06:51

Understanding Group Permissions

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