[Unit]
Description=roscore starter
After=NetworkManager.service time-sync.target

[Service]
# Start roscore as a fork and then wait for the tcp port to be opened
# —————————————————————-
# Source all the environment variables, start roscore in a fork
# Since the service type is forking, systemd doesn’t mark it as
# ‘started’ until the original process exits, so we have the
# non-forked shell wait until it can connect to the tcp opened by
# roscore, and then exit, preventing conflicts with dependant services
Type=forking
ExecStart=/bin/bash -c "source /opt/ros/melodic/setup.bash;roscore & while ! echo exit |nc localhost 11311 > /dev/null;do sleep 1;done"

[Install]
WantedBy=multi-user.target