Como habilitar acesso root via SSH

Quando tento instalar no kali linux usando o comando:# apt-get install openssh-server ele sempre retorna a mensagem: Reading package lists... Done
Building dependency tree
Reading state information... Done
Package openssh-server is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
openssh-sftp-server

E: Package 'openssh-server' has no installation candidate

sabe me dizer oq fazer? eu qria acessar o kali linux pelo putty no meu windows

#apt-get install ssh