shadow-useradd package to add more users to the system -- for Samba usage. It does not accept user names with a dot (or period) character.
root@OpenWrt:~# useradd --create-home --shell "/bin/ash" "firstname.lastname"; useradd: invalid user name 'firstname.lastname'
I decided to manually edit the user and group name in
/etc/group, and it works fine, which means Linux does allow that character.
What is the problem with that character? And is it a common issue of
useradd command across all Linux distros or just OpenWrt?