Q. Why Linux usernames with capital letters are not working? When I run adduser command I get bad username or Use the `–force-badname’ message. I am using Debian Linux.
A. You should always try to avoid Linux usernames with capital letters in them. Many server program such as FTP server or sendmail makes no difference between a user name ‘Vivek’ and ‘vivek’. Further many windows clients such as OE or IE make no distinction between capital letters.
Hence most Linux distro will disable Linux usernames with capital letters in them via adduser or other gui tools such as redhat-config-users (fedora core/centos/RHEL).