Ssh server. File transfers with protocol SCP and SFTP are available. Command line is also available (beta version). Command line needs "/system/bin/sh" preinstalled.
To start the server automatically use application "Autostart and StaY!" https://play.google.com/store/apps/details?id=com.atasoglou.autostartandstay or also Tasker with the intents provided.
Safety starts with understanding how developers collect and share your data. Data privacy and security practices may vary based on your use, region, and age. The developer provided this information and may update it over time.