Al querer agregar un repositorio aparece el error:
gpg: failed to start the dirmngr '/usr/bin/dirmngr': No such file or directory
AcompaƱado de:
gpg: connecting dirmngr at '/tmp/tmpyq7kwe2x/S.dirmngr' failed: No such file or directory
gpg: keyserver receive failed: No dirmngr
Para solucionarlo hay que instalar el paquete dirmgr:
sudo apt-get install dirmngr
y listo.