查了LightDM的官方文档,发现也不是很难。
只要在/usr/share/lightdm/lightdm.conf.d/目录下新建一个自己的配置文件就可以了。
System provided configuration should be stored in /usr/share/lightdm/lightdm.conf.d/. System administrators can override this configuration by adding files to /etc/lightdm/lightdm.conf.d/ and /etc/lightdm/lightdm.conf. Files are read in the above order and combined together to make the LightDM configuration.
参考资料【1】