On ubuntu server, I've noticed more than once now that after adding a user to a group that user doesn't have group permissions until I reboot the system. For example:
User 'hudson' needs permission to read directory 'root:shadow /etc/shadow' So I add hudson to the shadow group. hudson still cannot read. So, I 'sudo shutdown -h -r now' and when the system comes up again user hudson can read.
Is a reboot required or is there a better way to get permissions applied after adding the user to the group?