How do I log in with a user that is not included on the list in Ubuntu 12.04?

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http://askubuntu.com – I am using Ubuntu 12.04 64 bit. I have created a system user so as to keep it out of the login screen with sudo adduser --group --system markpaskal, but I cannot login from the greeter because there is no 'Other' option. Short of stopping lightdm and using startx from a virtual terminal, do I have any way of logging in to this account? (HowTos)