Thanks a lot!!!

Your two points were right (root=11.22.33.44:/srv/fai/nfsroot.... and 
rd.net.timeout.***).
This is how my pxeconfig now works:

# generated by fai-chboot for host 90:1B:0E:2B:CC:87 with IP no IP
default fai-generated

label fai-generated
kernel vmlinuz-4.19.0-6-amd64
append initrd=initrd.img-4.19.0-6-amd64 ip=dhcp  
root=172.16.7.152:/srv/fai/nfsroot:vers=3 rootovl  
FAI_FLAGS=verbose,sshd,createvt 
FAI_CONFIG_SRC=nfs://172.16.7.152/srv/fai/config FAI_ACTION=install 
rd.net.timeout.carrier=15


--
Markus

On 06.01.20 00:12, Thomas Lange wrote:
This is your kernel cmdline:

Command line: BOOT_IMAGE=vmlinuz-4.19.0-6-amd64 
initrd=initrd.img-4.19.0-6-amd64 ip=dhcp  root=/srv/fai/nfsroot:vers=3 rootovl  
FAI_FLAGS=verbose,sshd,createvt,reboot 
FAI_CONFIG_SRC=nfs://faiserver/srv/fai/config FAI_ACTION=install rd.debug

I guess the problem is root=/srv/fai/nfsroot. You hit this bug because
your dhcp server is not the FAI install server.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=731244

The fix is easy, just add the IP of your install server like this
root=11.22.33.44:/srv/fai/nfsroot....

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