member of www-data but it doesn't show in groups

Question

When I look at the groups that user 'wim' is a member of, www-data group does not show. When I look at the members of www-data, user wim is listed.

$ groups
wim adm cdrom sudo dip plugdev lpadmin sambashare
$ members wim
wim
$ members www-data
www-data wim

When trying to rename a file that is owned by www-data with 764 file permissions as user wim I get a 'permission denied' message.

$ ls -la htmlKauPriceListSingleProductGTS.inc 
-rwxrw-r-- 1 www-data www-data 3440  2月 12 14:46 htmlKauPriceListSingleProductGTS.inc
$ mv htmlKauPriceListSingleProductGTS.inc ZZZhtmlKauPriceListSingleProductGTS.inc
mv: cannot move 'htmlKauPriceListSingleProductGTS.inc' to 'ZZZhtmlKauPriceListSingleProductGTS.inc': Permission denied

Could someone please explain why user wim is in the group www-data but doesn't have the permissions to rename a file that is in the www-data group? And what I have to do to give user wim the necessary permissions to edit files in the www-data group?

thank you

Answer 1

Permission to create a file (used by the mv command), is given by the directory. You have not shown the mode of the directory, so we can not say more on this.

Adding a user to a group, just changes a file (/etc/groups). I process inherits groups from its parent, or is given groups by the login process (the login process has extra privileges to do this, and reads them from /etc/groups).

To get your shell to be a member of the new group, you can:

• Reboot
• Logout and back in again
• Use the newgrp command, to start a new shell. (this only affects child processes)

Answer 2

Restarting my system solved this problem.