Re: user permission inconsistency

["Karl E. Jorgensen" <karl@jorgensen.org.uk>]

Hi

On Mon, Dec 08, 2014 at 06:16:37PM +0100, alex wrote:
> 
> Hi everybody,
> 
> I observe a strange inconsistency in user permissions (jessie up to
> date; xfce4). Id est:
> 
> user@rheya:~$ ls -la /dev/ttyACM0
> crw-rw---- 1 root dialout 166, 0 Dec  8 17:25 /dev/ttyACM0
> 
> user@rheya:~$ id alex
> uid=1000(user) gid=1000(user) groups=1000(user),20(dialout)

This will show the group memberships of the "alex" user, if he was to
log in now.

> 
> user@rheya:~$ echo "\0" > /dev/ttyACM0
> bash: /dev/ttyACM0: Permission denied

Well - you do not appear to be logged in as "alex". You are "user" ??

> 
> although
> 
> root@rheya:~# echo "\0" > /dev/ttyACM0 && echo ok
> ok

running the "id" command without any parameters should show you the
group memberships of your shell.

> I *suspect* this is somehow related to systemd-logind (while systemd
> is not running as pid 1)
> 
> I just added user to group dialout (and astonished not to have to
> logout in order to have updated user groups list)

Well - if you run "id username", this will update immediately. 

But what matters is the group memberships of your *shell* - which it
will get at login-time...

Hope this helps
-- 
Karl E. Jorgensen