Thanks for your quick response.
Sure I can post it.
Download the certificate:
wget
http://www.tubit.tu-berlin.de/fileadmin ... tkette.pemCreate a subfolder in the certificate folder:
mkdir -p /usr/share/ca-certificates/tu-berlin.de
Move the certificate to the created folder:
mv TU-Berlin_Zertifikatkette.pem /usr/share/ca-certificates/tu-berlin.de/TU-Berlin_Zertifikatkette.pem
Add the root-certificates to the SSL-certificate-database:
echo tu-berlin.de/TU-Berlin_Zertifikatkette.pem >> /etc/ca-certificates.conf
Reload the certificate-database:
update-ca-certificates
And before I forget all steps shall be performed as root. I think I have to store the certificate somewhere in /etc/pki/tls/ but I neither know if that is correct nor what the command is to reload the database.