What good is a ssh-server when the machine doesn't even connect to the lan? Seriously, this is a fresh version of ubuntu server and i just updated the packages.

What you mean?

@Linux i took a pc, installed ubuntu server, connected to lan, upgraded packages and rebooted. I plugged out the monitor because i wanted to use ssh.
For an unknown reason this thing doesnt want to dhcp (it sends some packages, but no "normal dhcp"). I had to type dhclient enp1s0 manually to resolve this. I also tried to add sleep 10 && dhclient enp1s0 as root-crontab, but that didn't work.

Im done, i dont know what to do and i dont have the energy to inspect this issue. I'll just stop rebooting this.

@Linux update: it might not be the servers fault. Another of my devices (recently upgraded too) failed to get an ip address. Maybe my complex setup is at fault, there are a switch and a wifi repeater inbetween the devices and the router.

@YouAreAPIRate
It is almost the Network that is bad when DHCP fails :p