systemd + screen

[ocehb]

if [ $1 == "start" ]; then
  ps -C screen --no-headers -o pid,user,cmd
  if [ $? != 0 ]; then
    sudo -u user --login screen -Aa -dmS user-main -T screen-256color
  fi
fi

(user заменить на подходящего пользователя), и при старте запустится screen.
Проверка:

# systemctl start rc-local.service
# systemctl status rc-local.service
* rc-local.service - /etc/rc.d/rc.local Compatibility
   Loaded: loaded (/usr/lib/systemd/system/rc-local.service; enabled-runtime; vendor preset: disabled)
   Active: active (exited) since Fri 2017-11-17 14:29:12 EET; 5min ago
  Process: 1639 ExecStart=/etc/rc.d/rc.local start (code=exited, status=0/SUCCESS)
    Tasks: 0 (limit: 4915)
   CGroup: /system.slice/rc-local.service

Nov 17 14:29:12 vbox3.test.net systemd[1]: Starting /etc/rc.d/rc.local Compatibility...
Nov 17 14:29:12 vbox3.test.net rc.local[1639]:   782 user    SCREEN -Aa -dmS user-main -T screen-256color
Nov 17 14:29:12 vbox3.test.net rc.local[1639]:  1200 user    screen -ARxa
Nov 17 14:29:12 vbox3.test.net systemd[1]: Started /etc/rc.d/rc.local Compatibility.