The installer doesn't allow _ in usernames precisely because not everything accepts it. However, users-admin ought to be reasonably lenient with *existing* usernames, even if not when creating new ones.
** Changed in: user-setup (Ubuntu) Sourcepackagename: user-setup => gnome-system-tools -- Don't accept underscore "_" in usernames https://launchpad.net/bugs/49296 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
